• M. A. Sulimov, M. N. Sarychev, M. V. Yakushev, J. Márquez-Prieto, I. Forbes, Y. V. Ivanov, P. R. Edwards, A. V. Mudryi, J. Krustok, and R. W. Martin, “Effects of irradiation of ZnO/CdS/Cu₂ZnSnSe₄/Mo/glass solar cells by 10 MeV electrons on photoluminescence spectra,,” Materials Science in Semiconductor Processing, vol. 121, p. 105301, 2021.
    [BibTeX] [Abstract] [Download PDF]

    Solar cells with the structure ZnO/CdS/Cu₂ZnSnSe₄/Mo were studied by photoluminescence (PL) before and after irradiation with a dose of 1.8 × 10¹⁵ cm⁻² and then 5.4 × 10¹⁵ cm⁻² of 10 MeV electrons carried out at 77 K in liquid nitrogen bath. The low temperature PL spectra before irradiation revealed two bands, a broad and asymmetrical dominant FB band at 0.94 eV from the CZTSe layer and a lower intensity band HEB at 1.3 eV, generated by defects in the CdS buffer layer. Analysis of the excitation intensity and temperature dependencies suggested that the dominant band is the recombination of free electrons with holes localised at acceptors whose energy levels are affected by potential fluctuations of the valence band due to high concentrations of randomly distributed charged defects. Irradiation did not induce any new bands in the examined spectral range (from 0.5 µm to 1.65 µm) but reduced the intensity of both bands in the PL spectra measured at 77 K without warming the cells. The higher the dose the greater was the reduction. After this the cells were warmed to 300 K and moved to a variable temperature cryostat to measure excitation intensity and temperature dependencies of the PL spectra. After irradiation the rate of red shift of the FB band with temperature rise was found to increase. Electrons displace atoms in the lattice creating primary defects: interstitials and vacancies. These defects recombine during and shortly after irradiation forming secondary defect complexes which work as deep non-radiative traps of charge carriers reducing the PL intensity and increasing the rate of the temperature red shift. Irradiation did not affect the mean depth of the band tails estimated from the shape of the low energy side of the dominant PL band

    @Article{strathprints73346,
    author = {M. A. Sulimov and M. N. Sarychev and M. V. Yakushev and J. M{\'a}rquez-Prieto and I. Forbes and V. Yu. Ivanov and P. R. Edwards and A. V. Mudryi and J. Krustok and R. W. Martin},
    journal = {Materials Science in Semiconductor Processing},
    title = {Effects of irradiation of {ZnO/CdS/Cu₂ZnSnSe₄/Mo}/glass solar cells by 10 {MeV} electrons on photoluminescence spectra,},
    year = {2021},
    month = {July},
    pages = {105301},
    volume = {121},
    abstract = {Solar cells with the structure ZnO/CdS/Cu₂ZnSnSe₄/Mo were studied by photoluminescence (PL) before and after irradiation with a dose of 1.8 × 10¹⁵ cm⁻² and then 5.4 × 10¹⁵ cm⁻² of 10 MeV electrons carried out at 77 K in liquid nitrogen bath. The low temperature PL spectra before irradiation revealed two bands, a broad and asymmetrical dominant FB band at 0.94 eV from the CZTSe layer and a lower intensity band HEB at 1.3 eV, generated by defects in the CdS buffer layer. Analysis of the excitation intensity and temperature dependencies suggested that the dominant band is the recombination of free electrons with holes localised at acceptors whose energy levels are affected by potential fluctuations of the valence band due to high concentrations of randomly distributed charged defects. Irradiation did not induce any new bands in the examined spectral range (from 0.5 µm to 1.65 µm) but reduced the intensity of both bands in the PL spectra measured at 77 K without warming the cells. The higher the dose the greater was the reduction. After this the cells were warmed to 300 K and moved to a variable temperature cryostat to measure excitation intensity and temperature dependencies of the PL spectra. After irradiation the rate of red shift of the FB band with temperature rise was found to increase. Electrons displace atoms in the lattice creating primary defects: interstitials and vacancies. These defects recombine during and shortly after irradiation forming secondary defect complexes which work as deep non-radiative traps of charge carriers reducing the PL intensity and increasing the rate of the temperature red shift. Irradiation did not affect the mean depth of the band tails estimated from the shape of the low energy side of the dominant PL band},
    url = {https://strathprints.strath.ac.uk/73346/},
    }

  • M. V. Yakushev, M. A. Sulimov, C. Faugeras, A. V. Mudryi, and R. W. Martin, “The g-factor of CuGaSe₂ studied by circularly polarised magneto-reflectance,” Journal of Physics D: Applied Physics, vol. 53, p. 17LT02, 2020.
    [BibTeX] [Abstract] [Download PDF]

    High structural quality single crystals of CuGaSe2 were studied using photoluminescence (PL), optical reflectivity (OR) and circularly polarised magneto-reflectance (MR) at 4.2K in magnetic fields B up to 14 T. At B = 0 T both the PL and OR spectra exhibited the A free exciton, associated with the uppermost sub-band of the valence band of CuGaSe2 split by the tetragonal distortion in the lattice. The magnetic field induced a blue shift of the exciton in the MR spectra. Analysis of the dependence of the spectral position of the A exciton on B in the MR spectra, measured for both right and left circular polarisations of light, enabled the magnitude of its effective g-factor to be determined g = 0.46.

    @Article{strathprints71602,
    author = {M. V. Yakushev and M. A. Sulimov and C. Faugeras and A. V. Mudryi and R. W. Martin},
    journal = {Journal of Physics D: Applied Physics},
    title = {The g-factor of {CuGaSe₂} studied by circularly polarised magneto-reflectance},
    year = {2020},
    month = {February},
    pages = {17LT02},
    volume = {53},
    abstract = {High structural quality single crystals of CuGaSe2 were studied using photoluminescence (PL), optical reflectivity (OR) and circularly polarised magneto-reflectance (MR) at 4.2K in magnetic fields B up to 14 T. At B = 0 T both the PL and OR spectra exhibited the A free exciton, associated with the uppermost sub-band of the valence band of CuGaSe2 split by the tetragonal distortion in the lattice. The magnetic field induced a blue shift of the exciton in the MR spectra. Analysis of the dependence of the spectral position of the A exciton on B in the MR spectra, measured for both right and left circular polarisations of light, enabled the magnitude of its effective g-factor to be determined g = 0.46.},
    keywords = {CuGaSe2, photoluminescence, PL, optical reflectivity, semiconductors, optical spectroscopy, magnetic fields, Physics, Atomic and Molecular Physics, and Optics},
    url = {https://strathprints.strath.ac.uk/71602/},
    }

  • M. V. Yakushev, M. A. Sulimov, J. Márquez-Prieto, I. Forbes, P. R. Edwards, V. D. Zhivulko, O. M. Borodavchenko, A. V. Mudryi, J. Krustok, and R. W. Martin, “A luminescence study of Cu₂ZnSnSe₄/Mo/glass films and solar cells with near stoichiometric copper content,” Journal of Physics D: Applied Physics, vol. 36, p. 61208, 2019.
    [BibTeX] [Abstract] [Download PDF]

    Cu2ZnSnSe4 (CZTSe) is one of the leading candidates for the absorber layer in sustainable solar cells. Thin films of CZTSe with a near stoichiometric [Cu]/[Zn+Sn] were used to produce solar cells with conversion efficiency {\ensuremath{\eta}} = 6.4\% by a standard solar cell processing including KCN etching and the deposition of CdS and ZnO. Both CZTSe films and solar cells were examined using photoluminescence (PL) to analyse the nature of radiative recombination and photoluminescence excitation (PLE) at 4.2 K to determine the bandgap (Eg). Low temperature PL spectra of the films reveal an intense band P1 at 0.81 eV and a low intensity band P2 at 0.93 eV. Their temperature and excitation intensity dependencies suggest that they both involve recombinations of free electrons with holes localised at acceptors with the energy level influenced by potential fluctuations in the valence band . We associate P1 and P2 with different fractions of CZTSe: with a lower and higher degree of order of Cu and Zn on the cati on sub-lattice, respectively. Device processing reduced the intensity of P1 by 2.5 whereas the intensity of P2 increased by a 1.5. We assign this to a low temperature annealing due to CdS and ZnO deposition which increased the fraction of CZTSe with high d egree of Cu/Zn order and decreased the fraction with low degree of Cu/Zn order. Device processing increased Eg, blue shifted P1, decreased its width, j-shift and the mean depth of potential fluctuations. These can also be related to the annealing and/or KCN etching and the chemical effect of Cd, due to CdS replacing copper at the CdS – CZTSe interface layer. Processing induced a new broad band P3 at 1.3 eV ( quenching with Ea = 200 meV ) which we attributed to defects in the CdS layer.

    @Article{strathprints66083,
    author = {M. V. Yakushev and M.A. Sulimov and J. M{\'a}rquez-Prieto and I. Forbes and P.R. Edwards and V.D. Zhivulko and O.M. Borodavchenko and A. V. Mudryi and J. Krustok and R. W. Martin},
    title = {A luminescence study of Cu₂ZnSnSe₄/Mo/glass films and solar cells with near stoichiometric copper content},
    journal = {Journal of Physics D: Applied Physics},
    year = {2019},
    volume = {36},
    pages = {061208},
    month = {November},
    note = {This is an author-created, un-copyedited version of an article accepted for publication in Journal of Physics D: Applied Physics. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at http://iopscience.iop.org/journal/0022-3727.},
    abstract = {Cu2ZnSnSe4 (CZTSe) is one of the leading candidates for the absorber layer in sustainable solar cells. Thin films of CZTSe with a near stoichiometric [Cu]/[Zn+Sn] were used to produce solar cells with conversion efficiency {\ensuremath{\eta}} = 6.4\% by a standard solar cell processing including KCN etching and the deposition of CdS and ZnO. Both CZTSe films and solar cells were examined using photoluminescence (PL) to analyse the nature of radiative recombination and photoluminescence excitation (PLE) at 4.2 K to determine the bandgap (Eg). Low temperature PL spectra of the films reveal an intense band P1 at 0.81 eV and a low intensity band P2 at 0.93 eV. Their temperature and excitation intensity dependencies suggest that they both involve recombinations of free electrons with holes localised at acceptors with the energy level influenced by potential fluctuations in the valence band . We associate P1 and P2 with different fractions of CZTSe: with a lower and higher degree of order of Cu and Zn on the cati on sub-lattice, respectively. Device processing reduced the intensity of P1 by 2.5 whereas the intensity of P2 increased by a 1.5. We assign this to a low temperature annealing due to CdS and ZnO deposition which increased the fraction of CZTSe with high d egree of Cu/Zn order and decreased the fraction with low degree of Cu/Zn order. Device processing increased Eg, blue shifted P1, decreased its width, j-shift and the mean depth of potential fluctuations. These can also be related to the annealing and/or KCN etching and the chemical effect of Cd, due to CdS replacing copper at the CdS - CZTSe interface layer. Processing induced a new broad band P3 at 1.3 eV ( quenching with Ea = 200 meV ) which we attributed to defects in the CdS layer.},
    keywords = {solar cells, photoluminescence, CZTSe, Physics, Physics and Astronomy(all)},
    url = {https://strathprints.strath.ac.uk/66083/}
    }

  • M. V. Yakushev, C. Faugeras, A. V. Mudryi, and R. W. Martin, “A magneto-reflectivity study of CuInTe₂ single crystals,” Physica Status Solidi B, vol. 257, p. 1900464, 2019.
    [BibTeX] [Abstract] [Download PDF]

    CuInTe2 single crystals were studied using optical magneto-reflectance (MR) in magnetic fields B up to 20 T at 4.2 K. The spectra exhibited the A and B free excitons blue shifting at increasing magnetic fields. Fitting quadratic functions to the experimental dependencies of the exciton spectral energy on B assuming a lowfield limit allowed determination of diamagnetic shift rates of 8.2?10-5 eV/T2 and 8.5?10-5 eV/T2 for the A and B free excitons, respectively. Exciton reduced masses of 0.0575m0 and 0.0568m0 (m0 is the free electron mass), Rydbergs of 6.2 meV and 6.1 meV, and Bohr radii 10.4 nm and 10.5 nm were then estimated. An electron effective mass of 0.062m0 and B sub-band effective hole mass of 0.70m0 were determined using a literature value of the A valence sub-band hole of 0.78m0 .

    @Article{strathprints69479,
    author = {Michael V. Yakushev and Clement Faugeras and Alexander V. Mudryi and Robert W. Martin},
    title = {A magneto-reflectivity study of CuInTe₂ single crystals},
    journal = {Physica Status Solidi B},
    year = {2019},
    volume = {257},
    pages = {1900464},
    month = {August},
    abstract = {CuInTe2 single crystals were studied using optical magneto-reflectance (MR) in magnetic fields B up to 20 T at 4.2 K. The spectra exhibited the A and B free excitons blue shifting at increasing magnetic fields. Fitting quadratic functions to the experimental dependencies of the exciton spectral energy on B assuming a lowfield limit allowed determination of diamagnetic shift rates of 8.2?10-5 eV/T2 and 8.5?10-5 eV/T2 for the A and B free excitons, respectively. Exciton reduced masses of 0.0575m0 and 0.0568m0 (m0 is the free electron mass), Rydbergs of 6.2 meV and 6.1 meV, and Bohr radii 10.4 nm and 10.5 nm were then estimated. An electron effective mass of 0.062m0 and B sub-band effective hole mass of 0.70m0 were determined using a literature value of the A valence sub-band hole of 0.78m0 .},
    keywords = {CuInTe2, excitons, magnetic field, effective masses, Physics, Physics and Astronomy(all)},
    url = {https://strathprints.strath.ac.uk/69479/},
    }

  • M. V. Yakushev, A. V. Mudryi, C. Faugeras, and R. W. Martin, “A magneto-reflectivity study of CuGaSe₂ single crystals,” Physica Status Solidi (RRL) – Rapid Research Letters, vol. 13, iss. 2, p. 1800374, 2019.
    [BibTeX] [Abstract] [Download PDF]

    CuGaSe₂ single crystals are studied using magneto-reflectivity at 4.2 K in magnetic fields B up to 20 T. The A and B free excitons, observed in the optical reflectivity spectra, blue shift with increasing B. A low-field perturbation approach within the anisotropic hydrogenic model is used to fit the dependence of the spectral position of these excitons on B. The A and B exciton reduced masses of 0.115m₀ and 0.108m0 (m₀ is the free electron mass), Rydbergs of 12.9 and 12.2meV, Bohr radii 5.08 and 5.4 nm, and effective hole masses of 0.64m₀ and 0.48m₀, respectively, are determined.

    @Article{strathprints68316,
    author = {Michael V. Yakushev and Alexander V. Mudryi and Clement Faugeras and Robert W. Martin},
    journal = {Physica Status Solidi (RRL) - Rapid Research Letters},
    title = {A magneto-reflectivity study of {CuGaSe₂} single crystals},
    year = {2019},
    month = {February},
    number = {2},
    pages = {1800374},
    volume = {13},
    abstract = {CuGaSe₂ single crystals are studied using magneto-reflectivity at 4.2 K in magnetic fields B up to 20 T. The A and B free excitons, observed in the optical reflectivity spectra, blue shift with increasing B. A low-field perturbation approach within the anisotropic hydrogenic model is used to fit the dependence of the spectral position of these excitons on B. The A and B exciton reduced masses of 0.115m₀ and 0.108m0 (m₀ is the free electron mass), Rydbergs of 12.9 and 12.2meV, Bohr radii 5.08 and 5.4 nm, and effective hole masses of 0.64m₀ and 0.48m₀, respectively, are determined.},
    keywords = {CuGaSe2, excitons, magnetic field, Physics, Physics and Astronomy(all)},
    url = {https://strathprints.strath.ac.uk/68316/},
    }

  • M. V. Yakushev, A. V. Mudryi, E. Kärber, P. R. Edwards, and R. W. Martin, “The band structure of CuInTe₂ studied by optical reflectivity,” Applied Physics Letters, vol. 114, iss. 6, p. 62103, 2019.
    [BibTeX] [Abstract] [Download PDF]

    CuInTe₂ is a semiconductor with high potential for use as a thermoelectric material and as the absorber in thin film solar cells. Studying the optical reflectivity spectra of CuInTe₂ single crystals resolves resonances at 1.054 eV and 1.072 eV, which are assigned to the A and B free excitons. Photoluminescence spectra exhibited a peak due to the A free exciton at 1.046 eV. Varshni coefficients were found for both excitons. Zero temperature bandgaps EgA = 1.060 eV and EgB = 1.078 eV were determined for the A and B valence sub-bands, respectively. The splitting due to crystal-field ΔCF and spin-orbit effects ΔSO were calculated as -26.3 meV and 610 meV, respectively, using the determined EgA and EgB and a literature value of EgC.

    @Article{strathprints66980,
    author = {M. V. Yakushev and A. V. Mudryi and E. Kärber and P. R. Edwards and R. W. Martin},
    title = {The band structure of CuInTe₂ studied by optical reflectivity},
    journal = {Applied Physics Letters},
    year = {2019},
    volume = {114},
    number = {6},
    pages = {062103},
    month = {February},
    abstract = {CuInTe₂ is a semiconductor with high potential for use as a thermoelectric material and as the absorber in thin film solar cells. Studying the optical reflectivity spectra of CuInTe₂ single crystals resolves resonances at 1.054 eV and 1.072 eV, which are assigned to the A and B free excitons. Photoluminescence spectra exhibited a peak due to the A free exciton at 1.046 eV. Varshni coefficients were found for both excitons. Zero temperature bandgaps EgA = 1.060 eV and EgB = 1.078 eV were determined for the A and B valence sub-bands, respectively. The splitting due to crystal-field ΔCF and spin-orbit effects ΔSO were calculated as -26.3 meV and 610 meV, respectively, using the determined EgA and EgB and a literature value of EgC.},
    keywords = {optical reflectivity, CuInTe2, semiconductors, electronic band structures, chalcopyrites, Optics. Light, Atomic and Molecular Physics, and Optics},
    url = {https://strathprints.strath.ac.uk/66980/}
    }

  • M. A. Sulimov, M. V. Yakushev, J. Márquez-Prieto, I. Forbes, P. R. Edwards, V. D. Zhivulko, O. M. Borodavchenko, A. V. Mudryi, J. Krustok, and R. W. Martin, “Effects of selenisation temperature on photoluminescence and photoluminescence excitation spectra of ZnO/CdS/Cu₂ZnSnSe₄/Mo/glass,” Thin Solid Films, vol. 672, pp. 146-151, 2019.
    [BibTeX] [Abstract] [Download PDF]

    The effect of solar cell processing (including etching in KCN along with deposition of CdS and ZnO) on photoluminescence (PL) spectra and bandgap Eg (measured at 4.2 K by photoluminescence excitation) of Cu2ZnSnSe4 films, produced by selenising metallic precursors at 450 °C, 500 °C and 550 °C, was studied. Temperature and excitation intensity analysis of the P1 dominant band in the PL spectra of solar cells suggests that after processing this band still can be assigned to the free-to-bound recombination of free electrons with holes bound at deep acceptor levels influenced by valence band-tails. However processing increased the intensity of P1 and blue shifted it. The strongest effect was observed for the film selenised at 500 °C. For the film selenised at 450 °C the blue shift and increase in the intensity were smaller and only a slight intensity rise was found for the film selenised at 550 °C. The intensity increase we assign to a reduction in the concentration of non-radiative recombination centers on the surface because of the etching and changes in doping due to inter-diffusion of Cd, S, Se and Zn after the deposition of CdS. Such an inter-diffusion depends on the elemental composition of the films defining the chemistry of defects and influencing Eg which increased in the film selenised at 500 °C but decreased in the other films. Processing increased the P1 shift rate (j-shift) with excitation power change in all the films demonstrating a higher compensation degree in the solar cells which is consistent with the formation of an interface layer containing new donors CdCu.

    @Article{strathprints66586,
    author = {M.A. Sulimov and M.V. Yakushev and J. M{\'a}rquez-Prieto and I. Forbes and P.R. Edwards and V.D. Zhivulko and O.M. Borodavchenko and A. V. Mudryi and J. Krustok and R.W. Martin},
    title = {Effects of selenisation temperature on photoluminescence and photoluminescence excitation spectra of ZnO/CdS/Cu₂ZnSnSe₄/Mo/glass},
    journal = {Thin Solid Films},
    year = {2019},
    volume = {672},
    pages = {146-151},
    month = {January},
    abstract = {The effect of solar cell processing (including etching in KCN along with deposition of CdS and ZnO) on photoluminescence (PL) spectra and bandgap Eg (measured at 4.2 K by photoluminescence excitation) of Cu2ZnSnSe4 films, produced by selenising metallic precursors at 450 °C, 500 °C and 550 °C, was studied. Temperature and excitation intensity analysis of the P1 dominant band in the PL spectra of solar cells suggests that after processing this band still can be assigned to the free-to-bound recombination of free electrons with holes bound at deep acceptor levels influenced by valence band-tails. However processing increased the intensity of P1 and blue shifted it. The strongest effect was observed for the film selenised at 500 °C. For the film selenised at 450 °C the blue shift and increase in the intensity were smaller and only a slight intensity rise was found for the film selenised at 550 °C. The intensity increase we assign to a reduction in the concentration of non-radiative recombination centers on the surface because of the etching and changes in doping due to inter-diffusion of Cd, S, Se and Zn after the deposition of CdS. Such an inter-diffusion depends on the elemental composition of the films defining the chemistry of defects and influencing Eg which increased in the film selenised at 500 °C but decreased in the other films. Processing increased the P1 shift rate (j-shift) with excitation power change in all the films demonstrating a higher compensation degree in the solar cells which is consistent with the formation of an interface layer containing new donors CdCu.},
    keywords = {copper zinc tin selenide, solar cells, photoluminescence, selenisation, optical spectroscopy, Physics, Materials Chemistry, Surfaces and Interfaces, Electronic, Optical and Magnetic Materials, Surfaces, Coatings and Films, Metals and Alloys},
    url = {https://strathprints.strath.ac.uk/66586/}
    }

  • M. V. Yakushev, A. V. Rodina, R. P. Seisyan, Y. E. Kitaev, S. A. Vaganov, M. A. Abdullaev, A. V. Mudryi, T. V. Kuznetsova, C. Faugeras, and R. W. Martin, “Electronic energy band parameters of CuInSe₂ : Landau levels in magnetotransmission spectra,” Physical Review B: Condensed Matter and Materials Physics, vol. 100, iss. 23, p. 235202, 2019.
    [BibTeX] [Abstract] [Download PDF]

    Magnetotransmission (MT) at magnetic fields up to 29 T was used to study the electronic structure of CuInSe2 in thin polycrystalline films. The zero field absorption spectra exhibited resolved A, B, and C free excitons. Quantum oscillations, due to diamagnetic excitons comprising electrons and holes from Landau levels quantized in the conduction and valence band, respectively, appeared in the MT spectra at fields over 5 T. Spectral energies of Landau levels and binding energies of the corresponding diamagnetic excitons, theoretically calculated assuming a quasicubic approximation of the CuInSe2 tetragonal lattice structure, helped to identify the character of the experimentally observed diamagnetic excitons. Spectral energies of diamagnetic excitons in the MT spectra with different circular polarizations were used to determine the electron and light hole effective masses, whereas heavy hole masses as well as the {\ensuremath{\gamma}} and {\ensuremath{\gamma}}1 Luttinger parameters, Ep Kane energy, and F parameter of the influence of remote bands, as well as their polaron values, were calculated using the Luttinger theory.

    @Article{strathprints71034,
    author = {M. V. Yakushev and A. V. Rodina and R. P. Seisyan and Yu. E. Kitaev and S. A. Vaganov and M. A. Abdullaev and A. V. Mudryi and T. V. Kuznetsova and C. Faugeras and R. W. Martin},
    title = {Electronic energy band parameters of {CuInSe₂} : {L}andau levels in magnetotransmission spectra},
    journal = {Physical Review B: Condensed Matter and Materials Physics},
    year = {2019},
    volume = {100},
    number = {23},
    pages = {235202},
    month = dec,
    abstract = {Magnetotransmission (MT) at magnetic fields up to 29 T was used to study the electronic structure of CuInSe2 in thin polycrystalline films. The zero field absorption spectra exhibited resolved A, B, and C free excitons. Quantum oscillations, due to diamagnetic excitons comprising electrons and holes from Landau levels quantized in the conduction and valence band, respectively, appeared in the MT spectra at fields over 5 T. Spectral energies of Landau levels and binding energies of the corresponding diamagnetic excitons, theoretically calculated assuming a quasicubic approximation of the CuInSe2 tetragonal lattice structure, helped to identify the character of the experimentally observed diamagnetic excitons. Spectral energies of diamagnetic excitons in the MT spectra with different circular polarizations were used to determine the electron and light hole effective masses, whereas heavy hole masses as well as the {\ensuremath{\gamma}} and {\ensuremath{\gamma}}1 Luttinger parameters, Ep Kane energy, and F parameter of the influence of remote bands, as well as their polaron values, were calculated using the Luttinger theory.},
    keywords = {electronic energy band parameters, CuInSe2, magnetotransmission spectra, MT, Landau levels, energies, Physics, Nuclear and High Energy Physics},
    url = {https://strathprints.strath.ac.uk/71034/},
    }

  • M. A. Sulimov, M. V. Yakushev, I. Forbes, J. M. Prieto, A. V. Mudryi, J. Krustok, P. R. Edwards, and R. W. Martin, “A PL and PLE study of high Cu content Cu₂ZnSnSe₄ films on Mo/glass and solar cells,” Physics of the Solid State, vol. 61, p. 908–917, 2019.
    [BibTeX] [Abstract] [Download PDF]

    Cu₂ZnSnSe₄(CZTSe) is amongst leading candidates for the absorber layer in sustainable solar cells. We examine CZTSe thin films with [Cu]/[Zn + Sn] of 0.99 and [Zn]/[Sn] of 1.07, deposited on Mo/glass substrates, and solar cells fabricated from these films. The bandgap (Eg) of the as deposited films and solar cells was examined by photoluminescence excitation (PLE) whereas the temperature and excitation intensity dependence of photoluminescence (PL) spectra was used to examine the nature of radiative recombination. The 6 K PL spectra of CZTSe/Mo exhibit an intense broad and asymmetrical band P1 at 0.822 eV and a lower intensity band P2 at 0.93 eV. The shape of this band, high rates of blue shift with excitation intensity rise ( j-shift) j(P1) = 14 meV and j(P2) = 8 meV per decade, and red shifts of both bands with increasing temperature suggest that both bands are associated with valence band tails due to potential fluctuations caused by high populations of charged defects. The mean depth of such fluctuation γ of 24 meV was estimated from the low energy side of P1. Device processing increased Eg, blue shifted P1, decreased its width, j-shift and the mean depth of potential fluctuations. These can be due to the annealing and/or can partly be related to KCN etching and the chemical effect of Cd, from CdS replacing copper at the CdS–CZTSe interface layer. Processing induced a new broad band P3 at 1.3 eV (quenching with Ea = 200 meV). We attributed P3 to defects in the CdS layer.

    @Article{Sulimov2019PSS61,
    author = {M. A. Sulimov and M. V. Yakushev and I. Forbes and J. M. Prieto and A. V. Mudryi and Ju. Krustok and P. R. Edwards and R. W. Martin},
    title = {A {PL} and {PLE} study of high {Cu} content {Cu₂ZnSnSe₄} films on {Mo}/glass and solar cells},
    journal = {Physics of the Solid State},
    year = {2019},
    volume = {61},
    pages = {908--917},
    abstract = {Cu₂ZnSnSe₄(CZTSe) is amongst leading candidates for the absorber layer in sustainable solar cells. We examine CZTSe thin films with [Cu]/[Zn + Sn] of 0.99 and [Zn]/[Sn] of 1.07, deposited on Mo/glass substrates, and solar cells fabricated from these films. The bandgap (Eg) of the as deposited films and solar cells was examined by photoluminescence excitation (PLE) whereas the temperature and excitation intensity dependence of photoluminescence (PL) spectra was used to examine the nature of radiative recombination. The 6 K PL spectra of CZTSe/Mo exhibit an intense broad and asymmetrical band P1 at 0.822 eV and a lower intensity band P2 at 0.93 eV. The shape of this band, high rates of blue shift with excitation intensity rise ( j-shift) j(P1) = 14 meV and j(P2) = 8 meV per decade, and red shifts of both bands with increasing temperature suggest that both bands are associated with valence band tails due to potential fluctuations caused by high populations of charged defects. The mean depth of such fluctuation γ of 24 meV was estimated from the low energy side of P1. Device processing increased Eg, blue shifted P1, decreased its width, j-shift and the mean depth of potential fluctuations. These can be due to the annealing and/or can partly be related to KCN etching and the chemical effect of Cd, from CdS replacing copper at the CdS–CZTSe interface layer. Processing induced a new broad band P3 at 1.3 eV (quenching with Ea = 200 meV). We attributed P3 to defects in the CdS layer.},
    url = {https://dx.doi.org/10.1134/S1063783419050214}
    }

  • M. V. Yakushev, M. A. Sulimov, E. Skidchenko, J. Márquez-Prieto, I. Forbes, P. R. Edwards, M. V. Kuznetsov, V. D. Zhivulko, O. M. Borodavchenko, A. V. Mudryi, J. Krustok, and R. W. Martin, “Effects of Ar⁺ etching of Cu₂ZnSnSe₄ thin films : an x-ray photoelectron spectroscopy and photoluminescence study,” Journal of Vacuum Science and Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena, vol. 36, p. 61208, 2018.
    [BibTeX] [Abstract] [Download PDF]

    Cu2ZnSnSe4 (CZTSe) is a semiconductor used as the absorber layer in highly promising sustainable thin film solar cells. The authors study the effect of Ar+ etching of copper deficient and zinc excess CZTSe thin films deposited on Mo/glass substrates on the surface elemental composition, measured by x-ray photoelectron spectroscopy, and photoluminescence (PL) spectra. Low temperature PL spectra reveal a broad asymmetrical band at 0.95 eV. The temperature and excitation intensity dependencies of this band suggest that it is a free-to-bound (FB) recombination of electrons from the conduction band with holes localized at an acceptor affected by potential fluctuations. The surface composition of the as grown films demonstrates a strong copper deficiency: [Cu]/[Zn + Sn] = 0.33. The etching of the film surface using Ar+ beam increases [Cu]/[Zn + Sn] to 0.51, which is significantly smaller than that of 0.78 in the bulk, measured by wavelength dispersive x-ray analysis, demonstrating the presence on the surface of a copper-depleted layer. The Ar+ etching drastically reduces the FB band intensity by a factor of 4.5, broadens it and develops a low energy tail. Ar ions displace atoms in CZTSe lattice creating primary radiation defects, vacancies, and interstitials, which recombine at room temperature forming antisite defects with deep energy levels. Some of them generate the observed low energy tail and increase the mean depth of potential fluctuation {\ensuremath{\gamma}}, determined from the shape of the low energy side of FB band, from 24 meV before Ar+ etching to 35 meV after. Other deep defects work as nonradiative recombination centers reducing the intensity of the FB band.

    @Article{strathprints66330,
    author = {Michael V. Yakushev and Mikhail A. Sulimov and Ekaterina Skidchenko and Jose M{\'a}rquez-Prieto and Ian Forbes and Paul R. Edwards and Mikhail V. Kuznetsov and Vadim D. Zhivulko and Olga M. Borodavchenko and Alexander V. Mudryi and Juri Krustok and Robert W. Martin},
    title = {Effects of Ar⁺ etching of Cu₂ZnSnSe₄ thin films : an x-ray photoelectron spectroscopy and photoluminescence study},
    journal = {Journal of Vacuum Science and Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena},
    year = {2018},
    volume = {36},
    pages = {061208},
    month = {November},
    abstract = {Cu2ZnSnSe4 (CZTSe) is a semiconductor used as the absorber layer in highly promising sustainable thin film solar cells. The authors study the effect of Ar+ etching of copper deficient and zinc excess CZTSe thin films deposited on Mo/glass substrates on the surface elemental composition, measured by x-ray photoelectron spectroscopy, and photoluminescence (PL) spectra. Low temperature PL spectra reveal a broad asymmetrical band at 0.95 eV. The temperature and excitation intensity dependencies of this band suggest that it is a free-to-bound (FB) recombination of electrons from the conduction band with holes localized at an acceptor affected by potential fluctuations. The surface composition of the as grown films demonstrates a strong copper deficiency: [Cu]/[Zn + Sn] = 0.33. The etching of the film surface using Ar+ beam increases [Cu]/[Zn + Sn] to 0.51, which is significantly smaller than that of 0.78 in the bulk, measured by wavelength dispersive x-ray analysis, demonstrating the presence on the surface of a copper-depleted layer. The Ar+ etching drastically reduces the FB band intensity by a factor of 4.5, broadens it and develops a low energy tail. Ar ions displace atoms in CZTSe lattice creating primary radiation defects, vacancies, and interstitials, which recombine at room temperature forming antisite defects with deep energy levels. Some of them generate the observed low energy tail and increase the mean depth of potential fluctuation {\ensuremath{\gamma}}, determined from the shape of the low energy side of FB band, from 24 meV before Ar+ etching to 35 meV after. Other deep defects work as nonradiative recombination centers reducing the intensity of the FB band.},
    keywords = {Cu2ZnSnSe4, argon ion etching, photoluminescence, Physics, Condensed Matter Physics, Renewable Energy, Sustainability and the Environment, Electronic, Optical and Magnetic Materials},
    url = {https://strathprints.strath.ac.uk/66330/}
    }

  • I. E. Svitsiankou, V. N. Pavlovskii, E. V. Lutsenko, G. P. Yablonskii, A. V. Mudryi, O. M. Borodavchenko, V. D. Zhivulko, M. V. Yakushev, and R. Martin, “Stimulated emission and optical properties of solid solutions of Cu(In,Ga)Se₂ direct band gap semiconductors,” Journal of Applied Spectroscopy, vol. 85, iss. 2, p. 267–273, 2018.
    [BibTeX] [Abstract] [Download PDF]

    Stimulated emission, optical properties, and structural characteristics of non-irradiated and proton-irradiated Cu(In,Ga)Se₂ thin films deposited on soda lime glass substrates using co-evaporation of elements in a multistage process were investigated. X-ray diffraction analysis, scanning electron microscopy, X-ray spectral analysis with energy dispersion, low-temperature photoluminescence, optical transmittance and reflectance were used to study the films. Stimulated emission at low temperatures of ~20 K was found in non-irradiated and proton-irradiated Cu(In,Ga)Se₂ thin films upon excitation by laser pulses of nanosecond duration with a threshold power density of ~20 kW/cm². It was shown that the appearance and parameters of the stimulated emission depend strongly on the concentration of ion-induced defects in Cu(In,Ga)Se₂ thin films.

    @Article{strathprints64210,
    author = {I. E. Svitsiankou and V. N. Pavlovskii and E. V. Lutsenko and G. P. Yablonskii and A. V. Mudryi and O. M. Borodavchenko and V. D. Zhivulko and M. V. Yakushev and R. Martin},
    title = {Stimulated emission and optical properties of solid solutions of {Cu(In,Ga)Se₂} direct band gap semiconductors},
    journal = {Journal of Applied Spectroscopy},
    year = {2018},
    volume = {85},
    number = {2},
    pages = {267--273},
    month = {May},
    note = {This output is an English translation of an article published in published in Zhurnal Prikladnoi Spektroskopii, Vol. 85, No. 2, pp. 248-255, March-April, 2018.},
    abstract = {Stimulated emission, optical properties, and structural characteristics of non-irradiated and proton-irradiated Cu(In,Ga)Se₂ thin films deposited on soda lime glass substrates using co-evaporation of elements in a multistage process were investigated. X-ray diffraction analysis, scanning electron microscopy, X-ray spectral analysis with energy dispersion, low-temperature photoluminescence, optical transmittance and reflectance were used to study the films. Stimulated emission at low temperatures of ~20 K was found in non-irradiated and proton-irradiated Cu(In,Ga)Se₂ thin films upon excitation by laser pulses of nanosecond duration with a threshold power density of ~20 kW/cm². It was shown that the appearance and parameters of the stimulated emission depend strongly on the concentration of ion-induced defects in Cu(In,Ga)Se₂ thin films.},
    keywords = {Cu(In,Ga)Se, defect, proton, stimulated emission, thin film, Physics, Condensed Matter Physics, Spectroscopy},
    url = {https://strathprints.strath.ac.uk/64210/}
    }

  • I. E. Svitsiankou, V. N. Pavlovskii, E. V. Lutsenko, G. P. Yablonskii, A. V. Mudryi, O. M. Borodavchenko, V. D. Zhivulko, M. V. Yakushev, and R. Martin, “СТИМУЛИРОВАННОЕ ИЗЛУЧЕНИЕ И ОПТИЧЕСКИЕ СВОЙСТВА ТВЕРДЫХ РАСТВОРОВ ПРЯМОЗОННЫХ ПОЛУПРОВОДНИКОВ Cu(In,Ga)Se₂,” Zhurnal Prikladnoi Spektroskopii, vol. 85, iss. 2, pp. 248-255, 2018.
    [BibTeX] [Abstract] [Download PDF]

    Stimulated emission, optical properties, and structural characteristics of non-irradiated and proton-irradiated Cu(In,Ga)Se₂ thin films deposited on soda lime glass substrates using co-evaporation of elements in a multistage process were investigated. X-ray diffraction analysis, scanning electron microscopy, X-ray spectral analysis with energy dispersion, low-temperature photoluminescence, optical transmittance and reflectance were used to study the films. Stimulated emission at low temperatures of ~20 K was found in non-irradiated and proton-irradiated Cu(In,Ga)Se₂ thin films upon excitation by laser pulses of nanosecond duration with a threshold power density of ~20 kW/cm². It was shown that the appearance and parameters of the stimulated emission depend strongly on the concentration of ion-induced defects in Cu(In,Ga)Se₂ thin films.

    @Article{strathprints64209,
    author = {I. E. Svitsiankou and V. N. Pavlovskii and E. V. Lutsenko and G. P. Yablonskii and A. V. Mudryi and O. M. Borodavchenko and V. D. Zhivulko and M. V. Yakushev and R. Martin},
    title = {СТИМУЛИРОВАННОЕ ИЗЛУЧЕНИЕ И ОПТИЧЕСКИЕ СВОЙСТВА ТВЕРДЫХ РАСТВОРОВ ПРЯМОЗОННЫХ ПОЛУПРОВОДНИКОВ {Cu(In,Ga)Se₂}},
    journal = {Zhurnal Prikladnoi Spektroskopii},
    year = {2018},
    volume = {85},
    number = {2},
    pages = {248-255},
    month = {April},
    abstract = {Stimulated emission, optical properties, and structural characteristics of non-irradiated and proton-irradiated Cu(In,Ga)Se₂ thin films deposited on soda lime glass substrates using co-evaporation of elements in a multistage process were investigated. X-ray diffraction analysis, scanning electron microscopy, X-ray spectral analysis with energy dispersion, low-temperature photoluminescence, optical transmittance and reflectance were used to study the films. Stimulated emission at low temperatures of ~20 K was found in non-irradiated and proton-irradiated Cu(In,Ga)Se₂ thin films upon excitation by laser pulses of nanosecond duration with a threshold power density of ~20 kW/cm². It was shown that the appearance and parameters of the stimulated emission depend strongly on the concentration of ion-induced defects in Cu(In,Ga)Se₂ thin films.},
    keywords = {Cu(In,Ga)Se, defect, proton, stimulated emission, thin film, Physics, Physics and Astronomy(all)},
    url = {https://strathprints.strath.ac.uk/64209/}
    }

  • A. V. Mudryi, M. V. Yakushev, V. A. Volkov, V. D. Zhivulko, O. M. Borodavchenko, and R. W. Martin, “Influence of the growth method on the photoluminescence spectra and electronic properties of CuInS₂ single crystals,” Journal of Luminescence, vol. 186, p. 123–126, 2017.
    [BibTeX] [Abstract] [Download PDF]

    A comparative analysis of free and bound excitons in the photoluminescence (PL) spectra of CuInS₂ single crystals grown by the traveling heater (THM) and the chemical vapor transport (CVT) methods is presented. The values of the binding energy of the A free exciton (18.5 and 19.7 meV), determined by measurements of the spectral positions of the ground and excited states, allowed the Bohr radii (3.8 and 3.7 nm), bandgaps (1.5536 and 1.5548 eV) and dielectric constants (10.2 and 9.9) to be calculated for CuInS₂ crystals grown by THM and CVT, respectively.

    @Article{strathprints60887,
    author = {A.V. Mudryi and M.V. Yakushev and V.A. Volkov and V.D. Zhivulko and O.M. Borodavchenko and R.W. Martin},
    title = {Influence of the growth method on the photoluminescence spectra and electronic properties of {CuInS₂} single crystals},
    journal = {Journal of Luminescence},
    year = {2017},
    volume = {186},
    pages = {123--126},
    month = {June},
    abstract = {A comparative analysis of free and bound excitons in the photoluminescence (PL) spectra of CuInS₂ single crystals grown by the traveling heater (THM) and the chemical vapor transport (CVT) methods is presented. The values of the binding energy of the A free exciton (18.5 and 19.7 meV), determined by measurements of the spectral positions of the ground and excited states, allowed the Bohr radii (3.8 and 3.7 nm), bandgaps (1.5536 and 1.5548 eV) and dielectric constants (10.2 and 9.9) to be calculated for CuInS₂ crystals grown by THM and CVT, respectively.},
    keywords = {photoluminescence, CuInS2, excitons, traveling heater, chemical vapor transport, chalcopyrite semiconductor, growth method, Optics. Light, Atomic and Molecular Physics, and Optics},
    url = {http://strathprints.strath.ac.uk/60887/}
    }

  • M. V. Yakushev, M. A. Sulimov, J. Márquez-Prieto, I. Forbes, J. Krustok, P. R. Edwards, V. D. Zhivulko, O. M. Borodavchenko, A. V. Mudryi, and R. W. Martin, “Influence of the copper content on the optical properties of CZTSe thin films,” Solar Energy Materials and Solar Cells, vol. 168, pp. 69-77, 2017.
    [BibTeX] [Abstract] [Download PDF]

    We present an optical spectroscopy study of Cu₂ZnSnSe₄ (CZTSe) thin films deposited on Mo/glass substrates. The [Cu]/[Zn+Sn] ratio in these films varies from nearly stoichiometric to strongly Cu deficient and Zn rich. Increasing Cu deficiency and Zn excess widens the bandgap Eg, determined using photoluminescence excitation (PLE) at 4.2 K, from 0.99 eV to 1.03 eV and blue shifts the dominant band in the photoluminescence (PL) spectra from 0.83 eV to 0.95 eV. The PL spectra of the near stoichiometric film reveal two bands: a dominant band centred at 0.83 eV and a lower intensity one at 0.93 eV. The temperature and excitation intensity dependence of the PL spectra help to identify the recombination mechanisms of the observed emission bands as free-to-bound: recombination of free electrons with holes localised at acceptors affected by randomly distributed potential fluctuations. Both the mean depth of such fluctuations, determined by analysing the shape of the dominant bands, and the broadening energy, estimated from the PLE spectra, become smaller with increasing Cu deficiency and Zn excess which also widens Eg due to an improved ordering of the Cu/Zn atoms. These changes in the elemental composition induce a significant blue shift of the PL bands exceeding the Eg widening. This is attributed to a change of the dominant acceptor for a shallow one, and is beneficial for the solar cell performance. Film regions with a higher degree of Cu/Zn ordering are present in the near stoichiometric film generating the second PL band at 0.93 eV.

    @Article{strathprints60524,
    author = {M. V. Yakushev and M. A. Sulimov and J. M{\'a}rquez-Prieto and I. Forbes and J. Krustok and P. R. Edwards and V. D. Zhivulko and O. M. Borodavchenko and A. V. Mudryi and R. W. Martin},
    title = {Influence of the copper content on the optical properties of {CZTSe} thin films},
    journal = {Solar Energy Materials and Solar Cells},
    year = {2017},
    volume = {168},
    pages = {69-77},
    month = {April},
    abstract = {We present an optical spectroscopy study of Cu₂ZnSnSe₄ (CZTSe) thin films deposited on Mo/glass substrates. The [Cu]/[Zn+Sn] ratio in these films varies from nearly stoichiometric to strongly Cu deficient and Zn rich. Increasing Cu deficiency and Zn excess widens the bandgap Eg, determined using photoluminescence excitation (PLE) at 4.2 K, from 0.99 eV to 1.03 eV and blue shifts the dominant band in the photoluminescence (PL) spectra from 0.83 eV to 0.95 eV. The PL spectra of the near stoichiometric film reveal two bands: a dominant band centred at 0.83 eV and a lower intensity one at 0.93 eV. The temperature and excitation intensity dependence of the PL spectra help to identify the recombination mechanisms of the observed emission bands as free-to-bound: recombination of free electrons with holes localised at acceptors affected by randomly distributed potential fluctuations. Both the mean depth of such fluctuations, determined by analysing the shape of the dominant bands, and the broadening energy, estimated from the PLE spectra, become smaller with increasing Cu deficiency and Zn excess which also widens Eg due to an improved ordering of the Cu/Zn atoms. These changes in the elemental composition induce a significant blue shift of the PL bands exceeding the Eg widening. This is attributed to a change of the dominant acceptor for a shallow one, and is beneficial for the solar cell performance. Film regions with a higher degree of Cu/Zn ordering are present in the near stoichiometric film generating the second PL band at 0.93 eV.},
    keywords = {copper, thin films, optical spectroscopy, photoluminescence excitation, stoichiometric film, Cu2ZnSnSe4, defects, zinc, Physics, Surfaces, Coatings and Films, Electronic, Optical and Magnetic Materials, Renewable Energy, Sustainability and the Environment},
    url = {http://strathprints.strath.ac.uk/60524/},
    }

  • J. Márquez-Prieto, M. V. Yakushev, I. Forbes, J. Krustok, P. R. Edwards, V. D. Zhivulko, O. M. Borodavchenko, A. V. Mudryi, M. Dimitrievska, V. Izquierdo-Roca, N. Pearsall, and R. W. Martin, “Impact of the selenisation temperature on the structural and optical properties of CZTSe absorbers,” Solar Energy Materials and Solar Cells, vol. 152, p. 42–50, 2016.
    [BibTeX] [Abstract] [Download PDF]

    We present structural and optical spectroscopy studies of thin films of Cu2ZnSnSe4 (CZTSe) with strong copper deficiency deposited on Mo/Glass substrates and selenised at 450, 500 or 550 ?C. Solar cells fabricated from these films demonstrated efficiencies up to 7.4\% for selenisation at 500 ?C. Structural analysis based on X-ray diffraction and Raman spectroscopy revealed the presence of SnSe2 in the film selenised at 450 ?C but not detected in the films selenised at higher temperatures. A progressive decrease of the Sn and Se content was observed as the selenisation temperature increased. Photoluminescence excitation was used to determine the bandgaps at 4.2 K. Detailed measurements of the temperature and excitation intensity dependencies of the photoluminescence spectra allow the recombination mechanisms of the observed emission bands to be identified as band-to-impurity and band-to-band transitions, and their evolution with selenisation temperature changes to be analysed. The strongest band-to-band transition is recorded in the PL spectra of the film selenised at 500 ?C and can be observed from 6 K to room temperature. The compositional and structural changes in the films and their influence on the optoelectronic properties of CZTSe and solar cells are discussed.

    @Article{strathprints55956,
    author = {J. M{\'a}rquez-Prieto and M. V. Yakushev and I. Forbes and J. Krustok and P. R. Edwards and V. D. Zhivulko and O. M. Borodavchenko and A. V. Mudryi and M. Dimitrievska and V. Izquierdo-Roca and N. Pearsall and R. W. Martin},
    title = {Impact of the selenisation temperature on the structural and optical properties of {CZTSe} absorbers},
    journal = {Solar Energy Materials and Solar Cells},
    year = {2016},
    volume = {152},
    pages = {42--50},
    month = {April},
    abstract = {We present structural and optical spectroscopy studies of thin films of Cu2ZnSnSe4 (CZTSe) with strong copper deficiency deposited on Mo/Glass substrates and selenised at 450, 500 or 550 ?C. Solar cells fabricated from these films demonstrated efficiencies up to 7.4\% for selenisation at 500 ?C. Structural analysis based on X-ray diffraction and Raman spectroscopy revealed the presence of SnSe2 in the film selenised at 450 ?C but not detected in the films selenised at higher temperatures. A progressive decrease of the Sn and Se content was observed as the selenisation temperature increased. Photoluminescence excitation was used to determine the bandgaps at 4.2 K. Detailed measurements of the temperature and excitation intensity dependencies of the photoluminescence spectra allow the recombination mechanisms of the observed emission bands to be identified as band-to-impurity and band-to-band transitions, and their evolution with selenisation temperature changes to be analysed. The strongest band-to-band transition is recorded in the PL spectra of the film selenised at 500 ?C and can be observed from 6 K to room temperature. The compositional and structural changes in the films and their influence on the optoelectronic properties of CZTSe and solar cells are discussed.},
    keywords = {Cu2ZnSnSe4, selenisation, optical spectroscopy, structure, Physics, Surfaces, Coatings and Films, Electronic, Optical and Magnetic Materials, Renewable Energy, Sustainability and the Environment},
    url = {http://strathprints.strath.ac.uk/55956/}
    }

  • M. V. Yakushev, J. Krustok, M. Grossberg, V. A. Volkov, A. V. Mudryi, and R. W. Martin, “A photoluminescence study of CuInSe₂ single crystals ion implanted with 5 keV hydrogen,” Journal of Physics D: Applied Physics, vol. 49, iss. 10, p. 105108, 2016.
    [BibTeX] [Abstract] [Download PDF]

    CuInSe2 single crystals ion implanted with 5 keV hydrogen at doses from 3 {$\times$} 1014 to 1016 cm-2 are studied by photoluminescence (PL). The PL spectra before and after implantation reveal two bands, a main dominant band centred at 0.96 eV and a lower intensity band centred at 0.93 eV. Detailed analysis of the shape of these bands, their temperature and excitation intensity dependencies allow the recombination mechanisms to be identified as band-to-tail (BT) and band-to-impurity (BI), respectively. The implantation causes gradual red shifts of the bands increasing linearly with the dose. The average depth of potential fluctuations is also estimated to increase with the dose and saturates for doses above 1015 cm-2. A model is proposed which associates the potential fluctuations with the antisite defects copper on indium site and indium on copper site. The saturation is explained by full randomization of copper and indium atoms on the cation sub-lattice.

    @Article{strathprints56024,
    author = {M. V. Yakushev and J. Krustok and M. Grossberg and V. A. Volkov and A. V. Mudryi and R. W. Martin},
    title = {A photoluminescence study of {CuInSe₂} single crystals ion implanted with 5 {keV} hydrogen},
    journal = {Journal of Physics D: Applied Physics},
    year = {2016},
    volume = {49},
    number = {10},
    pages = {105108},
    month = {February},
    abstract = {CuInSe2 single crystals ion implanted with 5 keV hydrogen at doses from 3 {$\times$} 1014 to 1016 cm-2 are studied by photoluminescence (PL). The PL spectra before and after implantation reveal two bands, a main dominant band centred at 0.96 eV and a lower intensity band centred at 0.93 eV. Detailed analysis of the shape of these bands, their temperature and excitation intensity dependencies allow the recombination mechanisms to be identified as band-to-tail (BT) and band-to-impurity (BI), respectively. The implantation causes gradual red shifts of the bands increasing linearly with the dose. The average depth of potential fluctuations is also estimated to increase with the dose and saturates for doses above 1015 cm-2. A model is proposed which associates the potential fluctuations with the antisite defects copper on indium site and indium on copper site. The saturation is explained by full randomization of copper and indium atoms on the cation sub-lattice.},
    keywords = {CuInSe, ion-implantation, photoluminescence, Physics, Condensed Matter Physics, Electronic, Optical and Magnetic Materials, Acoustics and Ultrasonics, Surfaces, Coatings and Films},
    url = {http://strathprints.strath.ac.uk/56024/}
    }

  • I. E. Svitsiankou, V. N. Pavlovskii, E. Lutsenko, G. P. Yablonskii, A. V. Mudryi, V. Zhivulko, M. V. Yakushev, and R. W. Martin, “Stimulated emission and lasing in Cu(In,Ga)Se₂ thin films,” Journal of Physics D: Applied Physics, vol. 49, iss. 9, p. 95106, 2016.
    [BibTeX] [Abstract] [Download PDF]

    Stimulated emission and lasing in Cu(In,Ga)Se 2 thin films have been demonstrated at a temperature of 20 K using excitation by a nanosecond pulsed N 2 laser with power densities in the range from 2 to 100 kW cm ? 2 . Sharp narrowing of the photoluminescence band, superlinear dependence of its intensity on excitation laser power, as well as stabilization of the spectral position and of the full-width at half-maximum of the band were observed in the films at increasing excitation intensity. The stimulated emission threshold was determined to be 20 kW cm ? 2 . A gain value of 94 cm ? 1 has been estimated using the variable stripe length method. Several sharp laser modes near 1.13 eV were observed above the laser threshold of I thr {\texttt{\char126}} 50 kW cm ? 2

    @Article{strathprints55973,
    author = {I E Svitsiankou and V N Pavlovskii and EV Lutsenko and G P Yablonskii and A V Mudryi and VD Zhivulko and M V Yakushev and R W Martin},
    title = {Stimulated emission and lasing in {Cu(In,Ga)Se₂} thin films},
    journal = {Journal of Physics D: Applied Physics},
    year = {2016},
    volume = {49},
    number = {9},
    pages = {095106},
    month = {February},
    abstract = {Stimulated emission and lasing in Cu(In,Ga)Se 2 thin films have been demonstrated at a temperature of 20 K using excitation by a nanosecond pulsed N 2 laser with power densities in the range from 2 to 100 kW cm ? 2 . Sharp narrowing of the photoluminescence band, superlinear dependence of its intensity on excitation laser power, as well as stabilization of the spectral position and of the full-width at half-maximum of the band were observed in the films at increasing excitation intensity. The stimulated emission threshold was determined to be 20 kW cm ? 2 . A gain value of 94 cm ? 1 has been estimated using the variable stripe length method. Several sharp laser modes near 1.13 eV were observed above the laser threshold of I thr {\texttt{\char126}} 50 kW cm ? 2},
    keywords = {stimulated emission, lasing, gain, threshold, photoluminescence, Physics, Physics and Astronomy(all)},
    url = {http://strathprints.strath.ac.uk/55973/}
    }

  • M. V. Yakushev, J. Márquez-Prieto, I. Forbes, P. R. Edwards, V. D. Zhivulko, A. V. Mudryi, J. Krustok, and R. W. Martin, “Radiative recombination in Cu₂ZnSnSe₄ thin films with Cu deficiency and Zn excess,” Journal of Physics D: Applied Physics, vol. 48, iss. 47, p. 475109, 2015.
    [BibTeX] [Abstract] [Download PDF]

    Thin films of Cu2ZnSnSe4 (CZTSe) with copper de?ficiency and zinc excess were fabricated at Northumbria University by the selenisation of metallic precursors deposited on Mo/glass and bare glass substrates. Absorption and photoluminescence (PL) measurements were used to examine the ?film on glass whereas fi?lms on Mo/glass were used to produce a solar cell with ef?ficiency of 8.1\%. Detailed temperature and excitation intensity analysis of PL spectra allows identifi?cation of the main recombination mechanisms as band-to-tail and band-to-band transitions. The latter transition was observed in the spectra from 6 to 300 K.

    @Article{strathprints54657,
    author = {M V Yakushev and J M{\'a}rquez-Prieto and I Forbes and P R Edwards and V D Zhivulko and A V Mudryi and J Krustok and R W Martin},
    title = {Radiative recombination in {Cu₂ZnSnSe₄} thin films with {Cu} deficiency and {Zn} excess},
    journal = {Journal of Physics D: Applied Physics},
    year = {2015},
    volume = {48},
    number = {47},
    pages = {475109},
    month = {November},
    abstract = {Thin films of Cu2ZnSnSe4 (CZTSe) with copper de?ficiency and zinc excess were fabricated at Northumbria University by the selenisation of metallic precursors deposited on Mo/glass and bare glass substrates. Absorption and photoluminescence (PL) measurements were used to examine the ?film on glass whereas fi?lms on Mo/glass were used to produce a solar cell with ef?ficiency of 8.1\%. Detailed temperature and excitation intensity analysis of PL spectra allows identifi?cation of the main recombination mechanisms as band-to-tail and band-to-band transitions. The latter transition was observed in the spectra from 6 to 300 K.},
    keywords = {Cu2ZnSnSe4, solar cells, photoluminescence, Physics, Physics and Astronomy(all)},
    url = {http://strathprints.strath.ac.uk/54657/}
    }

  • M. V. Yakushev, A. V. Mudryi, O. M. Borodavchenko, V. A. Volkov, and R. W. Martin, “A photoluminescence study of excitonic grade CuInSe₂ single crystals irradiated with 6 MeV electrons,” Journal of Applied Physics, vol. 118, iss. 15, p. 155703, 2015.
    [BibTeX] [Abstract] [Download PDF]

    High-quality single crystals of CuInSe2 with near-stoichiometric elemental compositions were irradiated with 6 MeV electrons, at doses from 1015 to 3 {$\times$} 1018 cm?2, and studied using photoluminescence (PL) at temperatures from 4.2 to 300 K. Before irradiation, the photoluminescence spectra reveal a number of sharp and well resolved lines associated with free- and bound-excitons. The spectra also show broader bands relating to free-to-bound transitions and their phonon replicas in the lower energy region below 1.0 eV. The irradiation with 6 MeV electrons reduces the intensity of the free- and the majority of the bound-exciton peaks. Such a reduction can be seen for doses above 1016 cm?2. The irradiation induces new PL lines at 1.0215 eV and 0.9909 eV and also enhances the intensity of the lines at 1.0325 and 1.0102 eV present in the photoluminescence spectra before the irradiation. Two broad bands at 0.902 and 0.972 eV, respectively, are tentatively associated with two acceptor-type defects: namely, interstitial selenium (Sei) and copper on indium site (Cu In). After irradiation, these become more intense suggesting an increase in the concentration of these defects due to irradiation.

    @Article{strathprints54688,
    author = {M. V. Yakushev and A. V. Mudryi and O. M. Borodavchenko and V. A. Volkov and R. W. Martin},
    title = {A photoluminescence study of excitonic grade {CuInSe₂} single crystals irradiated with 6 {MeV} electrons},
    journal = {Journal of Applied Physics},
    year = {2015},
    volume = {118},
    number = {15},
    pages = {155703},
    month = {October},
    abstract = {High-quality single crystals of CuInSe2 with near-stoichiometric elemental compositions were irradiated with 6 MeV electrons, at doses from 1015 to 3 {$\times$} 1018 cm?2, and studied using photoluminescence (PL) at temperatures from 4.2 to 300 K. Before irradiation, the photoluminescence spectra reveal a number of sharp and well resolved lines associated with free- and bound-excitons. The spectra also show broader bands relating to free-to-bound transitions and their phonon replicas in the lower energy region below 1.0 eV. The irradiation with 6 MeV electrons reduces the intensity of the free- and the majority of the bound-exciton peaks. Such a reduction can be seen for doses above 1016 cm?2. The irradiation induces new PL lines at 1.0215 eV and 0.9909 eV and also enhances the intensity of the lines at 1.0325 and 1.0102 eV present in the photoluminescence spectra before the irradiation. Two broad bands at 0.902 and 0.972 eV, respectively, are tentatively associated with two acceptor-type defects: namely, interstitial selenium (Sei) and copper on indium site (Cu In). After irradiation, these become more intense suggesting an increase in the concentration of these defects due to irradiation.},
    keywords = {CuInSe2 , radiation damage, photoluminescence, Physics, Physics and Astronomy(all)},
    url = {http://strathprints.strath.ac.uk/54688/}
    }

  • M. V. Yakushev, I. Forbes, A. V. Mudryi, M. Grossberg, J. Krustok, N. S. Beattie, M. Moynihan, A. Rockett, and R. W. Martin, “Optical spectroscopy studies of Cu₂ZnSnSe₄ thin films,” Thin Solid Films, vol. 582, p. 154–157, 2015.
    [BibTeX] [Abstract] [Download PDF]

    Cu2ZnSnSe4 thin films were synthesised by selenisation of magnetron sputtered metal precursors. The band gap determined from the absorption spectra increases from 1.01 eV at 300 K to 1.05 eV at 4.2 K. In lower quality films photoluminescence spectra show a broad, low intensity asymmetric band associated with a recombination of free electrons and holes localised on acceptors in the presence of spatial potential fluctuations. In high quality material the luminescence band becomes intense and narrow resolving two phonon replicas. Its shifts at changing excitation power suggest donor?acceptor pair recombination mechanisms. The proposed model involving two pairs of donors and acceptors is supported by the evolution of the band intensity and spectral position with temperature. Energy levels of the donors and acceptors are estimated using Arrhenius quenching analysis.

    @Article{strathprints55983,
    author = {M.V. Yakushev and I. Forbes and A.V. Mudryi and M. Grossberg and J. Krustok and N.S. Beattie and M. Moynihan and A. Rockett and R.W. Martin},
    title = {Optical spectroscopy studies of {Cu₂ZnSnSe₄} thin films},
    journal = {Thin Solid Films},
    year = {2015},
    volume = {582},
    pages = {154--157},
    month = {May},
    abstract = {Cu2ZnSnSe4 thin films were synthesised by selenisation of magnetron sputtered metal precursors. The band gap determined from the absorption spectra increases from 1.01 eV at 300 K to 1.05 eV at 4.2 K. In lower quality films photoluminescence spectra show a broad, low intensity asymmetric band associated with a recombination of free electrons and holes localised on acceptors in the presence of spatial potential fluctuations. In high quality material the luminescence band becomes intense and narrow resolving two phonon replicas. Its shifts at changing excitation power suggest donor?acceptor pair recombination mechanisms. The proposed model involving two pairs of donors and acceptors is supported by the evolution of the band intensity and spectral position with temperature. Energy levels of the donors and acceptors are estimated using Arrhenius quenching analysis.},
    keywords = {Cu2ZnSnSe4, thin films, photoluminescence, defects, absorption, Physics, Physics and Astronomy(all)},
    url = {http://strathprints.strath.ac.uk/55983/}
    }

  • M. V. Yakushev, A. V. Rodina, G. M. Shuchalin, R. P. Seisian, M. A. Abdullaev, A. Rockett, V. D. Zhivulko, A. V. Mudryi, C. Faugeras, and R. W. Martin, “Landau levels of the C-exciton in CuInSe₂ studied by magneto-transmission,” Applied Physics Letters, vol. 105, iss. 14, p. 142103, 2014.
    [BibTeX] [Abstract] [Download PDF]

    The electronic structure of the solar cell absorber CuInSe2 is studied using magneto-transmission in thin polycrystalline films at magnetic fields up to 29 T. A, B, and C free excitons are resolved in absorption spectra at zero field and a Landau level fan generated by diamagnetic exciton recombination is observed for fields above 7 T. The dependence of the C band exciton binding energy on magnetic fields, calculated using a hydrogenic approximation, is used to determine the C exciton Rydberg at 0 T (8.5 meV), band gap (1.2828 eV), and hole effective mass mso = (0.31 {$\pm$} 0.12)m0 for the C valence sub-band.

    @Article{strathprints53685,
    author = {M. V. Yakushev and A. V. Rodina and G. M. Shuchalin and R. P. Seisian and M. A. Abdullaev and A. Rockett and V. D. Zhivulko and A. V. Mudryi and C. Faugeras and R. W. Martin},
    title = {Landau levels of the {C}-exciton in {CuInSe₂} studied by magneto-transmission},
    journal = {Applied Physics Letters},
    year = {2014},
    volume = {105},
    number = {14},
    pages = {142103},
    month = {October},
    note = {Copyright 2014 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Yakushev, M. V., Rodina, A. V., Shuchalin, G. M., Seisian, R. P., Abdullaev, M. A., Rockett, A., ... Martin, R. W. (2014). Landau levels of the C-exciton in CuInSe2 studied by magneto-transmission. Applied Physics Letters, 105(14), [142103]. and may be found at http://dx.doi.org/10.1063/1.4897995},
    abstract = {The electronic structure of the solar cell absorber CuInSe2 is studied using magneto-transmission in thin polycrystalline films at magnetic fields up to 29 T. A, B, and C free excitons are resolved in absorption spectra at zero field and a Landau level fan generated by diamagnetic exciton recombination is observed for fields above 7 T. The dependence of the C band exciton binding energy on magnetic fields, calculated using a hydrogenic approximation, is used to determine the C exciton Rydberg at 0 T (8.5 meV), band gap (1.2828 eV), and hole effective mass mso = (0.31 {$\pm$} 0.12)m0 for the C valence sub-band.},
    keywords = {excitons, magnetic fields, absorption spectra, Physics, Physics and Astronomy (miscellaneous)},
    url = {http://strathprints.strath.ac.uk/53685/}
    }

  • M. V. Yakushev, P. Maiello, T. Raadik, M. J. Shaw, P. R. Edwards, J. Krustok, A. V. Mudryi, I. Forbes, and R. W. Martin, “Investigation of the structural, optical and electrical properties of Cu3BiS3 semiconducting thin films,” Energy Procedia, vol. 60, p. 166–172, 2014.
    [BibTeX] [Abstract] [Download PDF]

    The elemental composition, structural, optical and electronic properties of p-type Cu3BiS3 thin films are investigated. The films are shown to be single phase orthorhombic, with a measured composition of Cu3.00Bi0.92S3.02. A surface oxidation layer is also clarified using energy dependent X-ray microanalysis. Photoreflectance spectra demonstrate two band gaps (EgX =1.24 eV and EgY =1.53 eV at 4 K) associated with the X and Y valence sub-bands. The photocurrent excitation measurements suggest a direct allowed nature of EgX. Photoluminescence spectra at 5 K reveal two broad emission bands at 0.84 and 0.99 eV quenching with an activation energy of 40 meV.

    @article{strathprints51127,
    volume = {60},
    title = {Investigation of the structural, optical and electrical properties of Cu3BiS3 semiconducting thin films},
    author = {M.V. Yakushev and P. Maiello and T. Raadik and M.J. Shaw and P.R. Edwards and J. Krustok and A.V. Mudryi and I. Forbes and R.W. Martin},
    year = {2014},
    pages = {166--172},
    journal = {Energy Procedia},
    keywords = {Cu3BiS3, thin films, solar cells, Raman spectroscopy, photoluminescence, photoreflectance, Physics, Energy(all)},
    url = {http://strathprints.strath.ac.uk/51127/},
    abstract = {The elemental composition, structural, optical and electronic properties of p-type Cu3BiS3 thin films are investigated. The films are shown to be single phase orthorhombic, with a measured composition of Cu3.00Bi0.92S3.02. A surface oxidation layer is also clarified using energy dependent X-ray microanalysis. Photoreflectance spectra demonstrate two band gaps (EgX =1.24 eV and EgY =1.53 eV at 4 K) associated with the X and Y valence sub-bands. The photocurrent excitation measurements suggest a direct allowed nature of EgX. Photoluminescence spectra at 5 K reveal two broad emission bands at 0.84 and 0.99 eV quenching with an activation energy of 40 meV.}
    }

  • M. V. Yakushev, P. Maiello, T. Raadik, M. J. Shaw, P. R. Edwards, J. Krustok, A. V. Mudryi, I. Forbes, and R. W. Martin, “Electronic and structural characterisation of Cu3BiS3 thin films for the absorber layer of sustainable photovoltaics,” Thin Solid Films, vol. 562, p. 195–199, 2014.
    [BibTeX] [Abstract] [Download PDF]

    Abstract Thin films of p-type Cu3BiS3 with an orthorhombic wittichenite structure, a semiconductor with high potential for thin film solar cell absorber layers, were synthesised by thermal annealing of Cu and Bi precursors, magnetron sputtered on Mo/glass substrate, with a layer of thermo-evaporated S. The elemental composition, structural and electronic properties are studied. The Raman spectrum shows four modes with the dominant peak at 292 cm-1. Photoreflectance spectra demonstrate two band gaps EgX and EgY, associated with the X and Y valence sub-bands, and their evolution with temperature. Fitting the temperature dependencies of the band-gaps gives values of 1.24 and 1.53 eV for EgX and EgY at 0 K as well as the average phonon energy. Photoluminescence spectra at 5 K reveal two bright and broad emission bands at 0.84 and 0.99 eV, which quench with an activation energy of 40 meV. The photocurrent excitation measurements demonstrate a photoresponse and suggest a direct allowed nature of the band gap.

    @article{strathprints48646,
    volume = {562},
    title = {Electronic and structural characterisation of Cu3BiS3 thin films for the absorber layer of sustainable photovoltaics},
    author = {M.V. Yakushev and P. Maiello and T. Raadik and M.J. Shaw and P.R. Edwards and J. Krustok and A.V. Mudryi and I. Forbes and R.W. Martin},
    year = {2014},
    pages = {195--199},
    note = {{\copyright} 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license},
    journal = {Thin Solid Films},
    keywords = {photoluminescence, thin films, solar cells, semiconductors, electronic structure, raman spectroscopy, photoreflectance, Physics, Physics and Astronomy(all)},
    url = {http://strathprints.strath.ac.uk/48646/},
    abstract = {Abstract Thin films of p-type Cu3BiS3 with an orthorhombic wittichenite structure, a semiconductor with high potential for thin film solar cell absorber layers, were synthesised by thermal annealing of Cu and Bi precursors, magnetron sputtered on Mo/glass substrate, with a layer of thermo-evaporated S. The elemental composition, structural and electronic properties are studied. The Raman spectrum shows four modes with the dominant peak at 292 cm-1. Photoreflectance spectra demonstrate two band gaps EgX and EgY, associated with the X and Y valence sub-bands, and their evolution with temperature. Fitting the temperature dependencies of the band-gaps gives values of 1.24 and 1.53 eV for EgX and EgY at 0 K as well as the average phonon energy. Photoluminescence spectra at 5 K reveal two bright and broad emission bands at 0.84 and 0.99 eV, which quench with an activation energy of 40 meV. The photocurrent excitation measurements demonstrate a photoresponse and suggest a direct allowed nature of the band gap.}
    }

  • M. V. Yakushev, F. Luckert, A. V. Rodina, C. Faugeras, A. V. Karotki, A. V. Mudryi, and R. Martin, “Anisotropy of effective masses in CuInSe₂,” Applied Physics Letters, vol. 101, p. 262101, 2012.
    [BibTeX] [Abstract] [Download PDF]

    Anisotropy of the valence band is experimentally demonstrated in CuInSe2, a key component of the absorber layer in one of the leading thin-film solar cell technology. By changing the orientation of applied magnetic fields with respect to the crystal lattice, we measure considerable differences in the diamagnetic shifts and effective g-factors for the A and B free excitons. The resulting free exciton reduced masses are combined with a perturbation model for non-degenerate independent excitons and theoretical dielectric constants to provide the anisotropic effective hole masses, revealing anisotropies of 5.5 (4.2) for the A (B) valence bands.

    @Article{strathprints42671,
    author = {Michael V Yakushev and Franziska Luckert and A.V. Rodina and C. Faugeras and A.V. Karotki and A.V. Mudryi and Robert Martin},
    title = {Anisotropy of effective masses in CuInSe₂},
    journal = {Applied Physics Letters},
    year = {2012},
    volume = {101},
    pages = {262101},
    month = {December},
    abstract = {Anisotropy of the valence band is experimentally demonstrated in CuInSe2, a key component of the absorber layer in one of the leading thin-film solar cell technology. By changing the orientation of applied magnetic fields with respect to the crystal lattice, we measure considerable differences in the diamagnetic shifts and effective g-factors for the A and B free excitons. The resulting free exciton reduced masses are combined with a perturbation model for non-degenerate independent excitons and theoretical dielectric constants to provide the anisotropic effective hole masses, revealing anisotropies of 5.5 (4.2) for the A (B) valence bands.},
    keywords = {anisotropy , CuInSe2, effective masses, valence band, thin-?lm solar cell technology, applied magnetic ?elds, crystal lattice, Physics, Physics and Astronomy (miscellaneous)},
    url = {http://strathprints.strath.ac.uk/42671/}
    }

  • F. Luckert, M. V. Yakushev, C. Faugeras, A. V. Karotki, A. V. Mudryi, and R. W. Martin, “Excitation power and temperature dependence of excitons in CuInSe₂,” Journal of Applied Physics, vol. 111, iss. 9, p. 93507, 2012.
    [BibTeX] [Abstract] [Download PDF]

    Excitonic recombination processes in high quality CuInSe2 single crystals have been studied by photoluminescence (PL) and reflectance spectroscopy as a function of excitation powers and temperature. Excitation power dependent measurements confirm the identification of well-resolved A and B free excitons in the PL spectra and analysis of the temperature quenching of these lines provides values for activation energies. These are found to vary from sample to sample, with values of 12.5 and 18.4meV for the A and B excitons, respectively, in the one showing the highest quality spectra. Analysis of the temperature and power dependent PL spectra from the bound excitonic lines, labelled M1, M2, and M3 appearing in multiplets points to a likely assignment of the hole involved in each case. The M1 excitons appear to involve a conduction band electron and a hole from the B valence band hole. In contrast, an A valence band hole appears to be involved for the M2 and M3 excitons. In addition, the M1 exciton multiplet seems to be due to the radiative recombination of excitons bound to shallow hydrogenic defects, whereas the excitons involved in M2 and M3 are bound to more complex defects. In contrast to the M1 exciton multiplet, the excitonic lines of M2 and M3 saturate at high excitation powers suggesting that the concentration of the defects involved is low. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4709448]

    @Article{strathprints40877,
    author = {F. Luckert and M. V. Yakushev and C. Faugeras and A. V. Karotki and A. V. Mudryi and R. W. Martin},
    title = {Excitation power and temperature dependence of excitons in CuInSe₂},
    journal = {Journal of Applied Physics},
    year = {2012},
    volume = {111},
    number = {9},
    pages = {093507},
    month = {May},
    abstract = {Excitonic recombination processes in high quality CuInSe2 single crystals have been studied by photoluminescence (PL) and reflectance spectroscopy as a function of excitation powers and temperature. Excitation power dependent measurements confirm the identification of well-resolved A and B free excitons in the PL spectra and analysis of the temperature quenching of these lines provides values for activation energies. These are found to vary from sample to sample, with values of 12.5 and 18.4meV for the A and B excitons, respectively, in the one showing the highest quality spectra. Analysis of the temperature and power dependent PL spectra from the bound excitonic lines, labelled M1, M2, and M3 appearing in multiplets points to a likely assignment of the hole involved in each case. The M1 excitons appear to involve a conduction band electron and a hole from the B valence band hole. In contrast, an A valence band hole appears to be involved for the M2 and M3 excitons. In addition, the M1 exciton multiplet seems to be due to the radiative recombination of excitons bound to shallow hydrogenic defects, whereas the excitons involved in M2 and M3 are bound to more complex defects. In contrast to the M1 exciton multiplet, the excitonic lines of M2 and M3 saturate at high excitation powers suggesting that the concentration of the defects involved is low. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4709448]},
    keywords = {band-edge photoluminescence, acceptors, CulnSe2, luminescence, emission, defect physics, radiative recombination, chalcopyrite semiconductor, single-crystals, excitation power , temperature dependence , excitons, Physics, Physics and Astronomy(all)},
    url = {http://strathprints.strath.ac.uk/40877/}
    }

  • F. Luckert, D. I. Hamilton, M. V. Yakushev, N. S. Beattie, G. Zoppi, M. Moynihan, I. Forbes, A. V. Karotki, A. V. Mudryi, M. Grossberg, J. Krustok, and R. W. Martin, “Optical properties of high quality Cu₂ZnSnSe₄ thin films,” Applied Physics Letters, vol. 99, iss. 6, p. 62104, 2011.
    [BibTeX] [Abstract] [Download PDF]

    Cu2ZnSnSe4 thin films, fabricated on bare or molybdenum coated glass substrates by magnetron sputtering and selenisation, were studied by a range of techniques. Photoluminescence spectra reveal an excitonic peak and two phonon replicas of a donor-acceptor pair (DAP) recombination. Its acceptor and donor ionisation energies are 27 and 7 meV, respectively. This demonstrates that high-quality Cu2ZnSnSe4 thin films can be fabricated. An experimental value for the longitudinal optical phonon energy of 28 meV was estimated. The band gap energy of 1.01 eV at room temperature was determined using optical absorption spectra.

    @Article{strathprints34031,
    author = {F. Luckert and D. I. Hamilton and M. V. Yakushev and N. S. Beattie and G. Zoppi and M. Moynihan and I. Forbes and A. V. Karotki and A. V. Mudryi and M. Grossberg and J. Krustok and R. W. Martin},
    title = {Optical properties of high quality Cu₂ZnSnSe₄ thin films},
    journal = {Applied Physics Letters},
    year = {2011},
    volume = {99},
    number = {6},
    pages = {062104},
    month = {August},
    abstract = {Cu2ZnSnSe4 thin films, fabricated on bare or molybdenum coated glass substrates by magnetron sputtering and selenisation, were studied by a range of techniques. Photoluminescence spectra reveal an excitonic peak and two phonon replicas of a donor-acceptor pair (DAP) recombination. Its acceptor and donor ionisation energies are 27 and 7 meV, respectively. This demonstrates that high-quality Cu2ZnSnSe4 thin films can be fabricated. An experimental value for the longitudinal optical phonon energy of 28 meV was estimated. The band gap energy of 1.01 eV at room temperature was determined using optical absorption spectra.},
    keywords = {photoluminescence, selenisation, dependence, energy, copper compounds, excitons, phonons, photoionisation, Raman spectra, semiconductor thin films, sputter deposition, tin compounds, zinc compounds, TIC - Bionanotechnology, Optics. Light, Physics and Astronomy (miscellaneous)},
    url = {http://strathprints.strath.ac.uk/34031/}
    }

  • H. Zachmann, S. Puttnins, M. V. Yakushev, F. Luckert, R. W. Martin, A. V. Karotki, V. F. Gremenok, and A. V. Mudryi, “Fabrication and characterisation of Cu(In,Ga)Se₂ solar cells on polyimide,” Thin Solid Films, vol. 519, iss. 21, p. 7264–7267, 2011.
    [BibTeX] [Abstract] [Download PDF]

    Solar cells with the structure ZnO:Al/i-ZnO/CdS/Cu(In,Ga)Se-2/Mo/polyimide were examined using a range of techniques. The elemental composition of the Cu(InGa)Se-2 (CIGS) layers, their crystalline structure and optical properties were studied. Photoluminescence (PL) spectra of the CIGS absorber layers were studied as functions of temperature (4.2-240 K) and excitation power density. The band gap energy E-g of the CIGS layers was determined by employing photoluminescence excitation (PLE) spectroscopy. The influence of sodium incorporation on the PL properties of CIGS was analysed. Correlations of the optical properties of the CIGS absorber layers and the photovoltaic parameters of the solar cells were revealed.

    @Article{strathprints32471,
    author = {H. Zachmann and S. Puttnins and M. V. Yakushev and F. Luckert and R. W. Martin and A. V. Karotki and V. F. Gremenok and A. V. Mudryi},
    title = {Fabrication and characterisation of Cu(In,Ga)Se₂ solar cells on polyimide},
    journal = {Thin Solid Films},
    year = {2011},
    volume = {519},
    number = {21},
    pages = {7264--7267},
    month = {August},
    abstract = {Solar cells with the structure ZnO:Al/i-ZnO/CdS/Cu(In,Ga)Se-2/Mo/polyimide were examined using a range of techniques. The elemental composition of the Cu(InGa)Se-2 (CIGS) layers, their crystalline structure and optical properties were studied. Photoluminescence (PL) spectra of the CIGS absorber layers were studied as functions of temperature (4.2-240 K) and excitation power density. The band gap energy E-g of the CIGS layers was determined by employing photoluminescence excitation (PLE) spectroscopy. The influence of sodium incorporation on the PL properties of CIGS was analysed. Correlations of the optical properties of the CIGS absorber layers and the photovoltaic parameters of the solar cells were revealed.},
    keywords = {cu(in,ga)se-2, solar cells, polyimide, photoluminescence, thin-films, high-efficiency, layers, na, TIC - Bionanotechnology, Physics, Materials Chemistry, Surfaces and Interfaces, Electronic, Optical and Magnetic Materials, Surfaces, Coatings and Films, Metals and Alloys},
    url = {http://strathprints.strath.ac.uk/32471/}
    }

  • M. V. Yakushev, F. Luckert, C. Faugeras, A. V. Karotki, A. V. Mudryi, and R. W. Martin, “Excited states of the A and B free excitons in CuInSe₂,” Japanese Journal of Applied Physics, vol. 50, iss. 5, p. 05FC03, 2011.
    [BibTeX] [Abstract] [Download PDF]

    CuInSe2 single crystals, grown by the vertical Bridgman technique were studied using polarisation resolved photoluminescence (PL) at cryogenic temperatures. The emission lines related to the first (n = 2) excited states for the A and B free excitons were observed in the PL spectra at 1.0481 and 1.0516 eV, respectively. The spectral positions of these lines were used to estimate accurate values for the A and B exciton binding energies (8.5 and 8.4 meV, respectively), Bohr radii (7.5 nm), band gaps (E-g(A) = 1.050 eV and E-g(B) = 1.054 eV), and the static dielectric constant (11.3) assuming the hydrogenic model.

    @Article{strathprints34032,
    author = {Michael V. Yakushev and Franziska Luckert and Clement Faugeras and Anatoli V. Karotki and Alexander V. Mudryi and Robert W. Martin},
    title = {Excited states of the A and B free excitons in CuInSe₂},
    journal = {Japanese Journal of Applied Physics},
    year = {2011},
    volume = {50},
    number = {5},
    pages = {05FC03},
    month = {May},
    abstract = {CuInSe2 single crystals, grown by the vertical Bridgman technique were studied using polarisation resolved photoluminescence (PL) at cryogenic temperatures. The emission lines related to the first (n = 2) excited states for the A and B free excitons were observed in the PL spectra at 1.0481 and 1.0516 eV, respectively. The spectral positions of these lines were used to estimate accurate values for the A and B exciton binding energies (8.5 and 8.4 meV, respectively), Bohr radii (7.5 nm), band gaps (E-g(A) = 1.050 eV and E-g(B) = 1.054 eV), and the static dielectric constant (11.3) assuming the hydrogenic model.},
    keywords = {optical properties, single crystals, Physics},
    url = {http://strathprints.strath.ac.uk/34032/}
    }

  • A. V. Karotki, A. V. Mudryi, M. V. Yakushev, F. Luckert, and R. Martin, “Structural and optical properties of CdS/Cu(In,Ga)Se₂ heterostructures irradiated by high energy electrons,” Journal of Applied Spectroscopy, vol. 77, iss. 5, p. 668–674, 2010.
    [BibTeX] [Abstract] [Download PDF]

    Thin films of Cu(In, Ga)Se-2 (CIGS) with a Ga/(Ga + In) ratio of similar to 0.27 corresponding to the standard elemental composition for solar-energy transducers were grown on Mo-coated glass substrates by the Cu, In, Ga, and Se co-evaporation technique from different sources. Transmission (T), photoluminescence (PL), and photoluminescence excitation (PLE) spectra at 4.2 K were used to analyze electronic properties in the asgrown and electron-irradiated CIGS films. The band-gap energy (E-g) of the CIGS films measured using both transmission and PLE methods was found to be about 1.28 eV at 4.2 K. Two deep bands in the PL spectra of the irradiated CIGS films, P-1 at similar to 0.91 eV and P-2 at similar to 0.77 eV, have been detected. These bands are tentatively associated with copper atoms substituting indium (Cu-In) and indium vacancies V-In, respectively, as the simplest radiation-induced defects.

    @Article{strathprints32495,
    author = {A. V. Karotki and A.V. Mudryi and Michael V Yakushev and Franziska Luckert and Robert Martin},
    title = {Structural and optical properties of CdS/Cu(In,Ga)Se₂ heterostructures irradiated by high energy electrons},
    journal = {Journal of Applied Spectroscopy},
    year = {2010},
    volume = {77},
    number = {5},
    pages = {668--674},
    month = {November},
    abstract = {Thin films of Cu(In, Ga)Se-2 (CIGS) with a Ga/(Ga + In) ratio of similar to 0.27 corresponding to the standard elemental composition for solar-energy transducers were grown on Mo-coated glass substrates by the Cu, In, Ga, and Se co-evaporation technique from different sources. Transmission (T), photoluminescence (PL), and photoluminescence excitation (PLE) spectra at 4.2 K were used to analyze electronic properties in the asgrown and electron-irradiated CIGS films. The band-gap energy (E-g) of the CIGS films measured using both transmission and PLE methods was found to be about 1.28 eV at 4.2 K. Two deep bands in the PL spectra of the irradiated CIGS films, P-1 at similar to 0.91 eV and P-2 at similar to 0.77 eV, have been detected. These bands are tentatively associated with copper atoms substituting indium (Cu-In) and indium vacancies V-In, respectively, as the simplest radiation-induced defects.},
    keywords = {Cu(In,Ga)Se2 , photoluminescence, electron irradiation, defects, Therapeutics. Pharmacology, Spectroscopy, Condensed Matter Physics},
    url = {http://strathprints.strath.ac.uk/32495/}
    }

  • M. V. Yakushev, F. Luckert, C. Faugeras, A. V. Karotki, A. V. Mudryi, and R. W. Martin, “Excited states of the free excitons in CuInSe₂ single crystals,” Applied Physics Letters, vol. 97, iss. 15, p. 152110, 2010.
    [BibTeX] [Abstract] [Download PDF]

    High-quality CuInSe2 single crystals were studied using polarization resolved photoluminescence (PL) and magnetophotoluminescence (MPL). The emission lines related to the first (n=2) excited states for the A and B free excitons were observed in the PL and MPL spectra at 1.0481 meV and 1.0516 meV, respectively. The spectral positions of these lines were used to estimate accurate values for the A and B exciton binding energies (8.5 meV and 8.4 meV, respectively), Bohr radii (7.5 nm), band gaps (E-g(A)=1.050 eV and E-g(B)=1.054 eV), and the static dielectric constant (11.3) assuming the hydrogenic model.

    @Article{strathprints29008,
    author = {M. V. Yakushev and F. Luckert and C. Faugeras and A. V. Karotki and A. V. Mudryi and R. W. Martin},
    title = {Excited states of the free excitons in CuInSe₂ single crystals},
    journal = {Applied Physics Letters},
    year = {2010},
    volume = {97},
    number = {15},
    pages = {152110},
    month = {October},
    abstract = {High-quality CuInSe2 single crystals were studied using polarization resolved photoluminescence (PL) and magnetophotoluminescence (MPL). The emission lines related to the first (n=2) excited states for the A and B free excitons were observed in the PL and MPL spectra at 1.0481 meV and 1.0516 meV, respectively. The spectral positions of these lines were used to estimate accurate values for the A and B exciton binding energies (8.5 meV and 8.4 meV, respectively), Bohr radii (7.5 nm), band gaps (E-g(A)=1.050 eV and E-g(B)=1.054 eV), and the static dielectric constant (11.3) assuming the hydrogenic model.},
    keywords = {radiative recombination, optical properties, crystals, excited states, free excitons, CulnSe2, single crystals, Physics, Physics and Astronomy (miscellaneous)},
    url = {http://strathprints.strath.ac.uk/29008/}
    }

  • F. Luckert, M. V. Yakushev, C. Faugeras, A. V. Karotki, A. V. Mudryi, and R. W. Martin, “Diamagnetic shift of the A free exciton in CuGaSe₂ single crystals,” Applied Physics Letters, vol. 97, iss. 16, p. 162101, 2010.
    [BibTeX] [Abstract] [Download PDF]

    Single crystals of CuGaSe2 were studied using magnetophotoluminescence inmagnetic fields up to 20 T at 4.2 K. The rate of the diamagnetic shift in the A free exciton peak was determined to be 9.82 x 10(-6) eV/T-2. This rate was used to calculate the reduced mass as 0.115m(0), the binding energy as 12.9 meV, the Bohr radius as 5.1 nm and an effective hole mass of 0.64m(0) (m(0) is the free electron mass) of the free A exciton using a low-field perturbation approach and the hydrogenic model.

    @Article{strathprints29007,
    author = {F. Luckert and M. V. Yakushev and C. Faugeras and A. V. Karotki and A. V. Mudryi and R. W. Martin},
    title = {Diamagnetic shift of the A free exciton in CuGaSe₂ single crystals},
    journal = {Applied Physics Letters},
    year = {2010},
    volume = {97},
    number = {16},
    pages = {162101},
    month = {October},
    abstract = {Single crystals of CuGaSe2 were studied using magnetophotoluminescence inmagnetic fields up to 20 T at 4.2 K. The rate of the diamagnetic shift in the A free exciton peak was determined to be 9.82 x 10(-6) eV/T-2. This rate was used to calculate the reduced mass as 0.115m(0), the binding energy as 12.9 meV, the Bohr radius as 5.1 nm and an effective hole mass of 0.64m(0) (m(0) is the free electron mass) of the free A exciton using a low-field perturbation approach and the hydrogenic model.},
    keywords = {electical properties, thin films, cuinse2, crystals, Physics, Physics and Astronomy (miscellaneous)},
    url = {http://strathprints.strath.ac.uk/29007/}
    }

  • F. Luckert, M. V. Yakushev, A. V. Mudryi, and R. W. Martin, “Excitons in chalcopyrite solar cell materials: CuInSe₂ and CuInS₂,” in 11th International Conference on Optics of Excitons in Confined Systems, 2010.
    [BibTeX] [Abstract] [Download PDF]

    A poster presentation on excitons in chalcopyrite solar cell materials

    @InProceedings{strathprints31043,
    author = {F. Luckert and M. V. Yakushev and A. V. Mudryi and R. W. Martin},
    title = {Excitons in chalcopyrite solar cell materials: CuInSe₂ and CuInS₂},
    booktitle = {11th International Conference on Optics of Excitons in Confined Systems},
    year = {2010},
    editor = {L Vina and C Tejedor and JM Calleja},
    month = {September},
    abstract = {A poster presentation on excitons in chalcopyrite solar cell materials},
    journal = {11th International Conference on Optics of Excitons in Confined Systems},
    keywords = {exciton, cell materials, CUINSE2, CUINS2, Physics},
    url = {http://strathprints.strath.ac.uk/31043/}
    }

  • A. V. Mudryi, V. F. Gremenok, A. V. Karotki, V. B. Zalesski, M. V. Yakushev, F. Luckert, and R. Martin, “Structural and optical properties of thin films of Cu(In,Ga)Se₂ semiconductor compounds,” Journal of Applied Spectroscopy, vol. 77, iss. 3, p. 371–377, 2010.
    [BibTeX] [Abstract] [Download PDF]

    The chemical composition of Cu(In,Ga)Se-2 (CIGS) semiconductor compounds is analyzed by local x-ray spectral microanalysis and scanning Auger electron spectroscopy. X-ray diffraction analysis reveals a difference in the predominant orientation of CIGS films depending on the technological conditions under which they are grown. The chemical composition is found to have a strong effect on the shift in the self-absorption edge of CIGS compounds. It is shown that a change in the relative proportion of Ga and In in CIGS semiconducting compounds leads to a change in the band gap E-g for this material in the 1.05-1.72 eV spectral range at 4.2 K.

    @Article{strathprints35401,
    author = {A. V. Mudryi and V. F. Gremenok and A. V. Karotki and V. B. Zalesski and M. V. Yakushev and F. Luckert and R. Martin},
    title = {Structural and optical properties of thin films of Cu(In,Ga)Se₂ semiconductor compounds},
    journal = {Journal of Applied Spectroscopy},
    year = {2010},
    volume = {77},
    number = {3},
    pages = {371--377},
    month = {July},
    abstract = {The chemical composition of Cu(In,Ga)Se-2 (CIGS) semiconductor compounds is analyzed by local x-ray spectral microanalysis and scanning Auger electron spectroscopy. X-ray diffraction analysis reveals a difference in the predominant orientation of CIGS films depending on the technological conditions under which they are grown. The chemical composition is found to have a strong effect on the shift in the self-absorption edge of CIGS compounds. It is shown that a change in the relative proportion of Ga and In in CIGS semiconducting compounds leads to a change in the band gap E-g for this material in the 1.05-1.72 eV spectral range at 4.2 K.},
    keywords = {chalcopyrite semiconductors, chemical composition, absorption coefficient, x-ray diffraction analysis, structure, CUINSE2 SINGLE-CRYSTALS, SOLAR-CELLS, EPITAXIAL LAYERS, CUIN1-XGAXSE2, QUALITY, PHOTOREFLECTANCE, PERFORMANCE, EFFICIENCY, Spectroscopy, Condensed Matter Physics},
    url = {http://strathprints.strath.ac.uk/35401/}
    }

  • A. V. Mudryi, A. V. Karotki, M. V. Yakushev, and R. W. Martin, “Photoluminescence of CuInS₂ single crystals grown by traveling heater and chemical vapor transport methods,” Journal of Applied Spectroscopy, vol. 76, iss. 2, p. 215–219, 2009.
    [BibTeX] [Abstract] [Download PDF]

    Photoluminescence of CuInS2 single crystals grown by both the traveling heater method (THM) and chemical vapor transport (CVT) has been investigated at 4.2, 78, and 300 K. Intense emission in the near-band-edge region caused by free and bound excitons has been detected for both types of crystals. Taking into account the energy position of the luminescence line of the ground (n = 1) and first excited (n = 2) states, the binding energy for free A excitons has been estimated to be about 19.7 and 18.5 meV for CuInS2 grown by CVT and THM, respectively.

    @Article{strathprints19124,
    author = {A.V. Mudryi and A.V. Karotki and M.V. Yakushev and R.W. Martin},
    title = {Photoluminescence of CuInS₂ single crystals grown by traveling heater and chemical vapor transport methods},
    journal = {Journal of Applied Spectroscopy},
    year = {2009},
    volume = {76},
    number = {2},
    pages = {215--219},
    month = {March},
    abstract = {Photoluminescence of CuInS2 single crystals grown by both the traveling heater method (THM) and chemical vapor transport (CVT) has been investigated at 4.2, 78, and 300 K. Intense emission in the near-band-edge region caused by free and bound excitons has been detected for both types of crystals. Taking into account the energy position of the luminescence line of the ground (n = 1) and first excited (n = 2) states, the binding energy for free A excitons has been estimated to be about 19.7 and 18.5 meV for CuInS2 grown by CVT and THM, respectively.},
    keywords = {CuInS2, photoluminescence, exciton, Physics, Spectroscopy, Condensed Matter Physics},
    url = {http://strathprints.strath.ac.uk/19124/}
    }

  • M. V. Yakushev, R. W. Martin, A. Babinski, and A. V. Mudryi, “Effects of magnetic fields on free excitons in CuInSe₂,” Physica Status Solidi C, vol. 6, iss. 5, p. 1086–1088, 2009.
    [BibTeX] [Abstract] [Download PDF]

    The effects of magnetic fields up to 20 T were studied in CuInSe2 single crystals using photoluminescence (PL) at 4.2 K. Diamagnetic shifts of the free A and B excitons measured in the PL spectra in CuInSe2 at 4.2 K tinder the magnetic fields were used to estimate the reduced masses (0.095m(0) for the A and 0.098m(0) for the B exciton), binding energies (7.0 meV for the A and 7.2 meV for the B exciton) and Bohr radii (7.6 nm for the A and 7.3 nm for the B exciton) of the free-excitons in CuInSe2 assuming that both excitons are isotropic and hydrogen-like. (C) 2009 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim

    @Article{strathprints37429,
    author = {M. V. Yakushev and R. W. Martin and A. Babinski and A. V. Mudryi},
    title = {Effects of magnetic fields on free excitons in CuInSe₂},
    journal = {Physica Status Solidi C},
    year = {2009},
    volume = {6},
    number = {5},
    pages = {1086--1088},
    month = {February},
    note = {Special Issue: 16th International Conference on Ternary and Multinary Compounds (ICTMC16)},
    abstract = {The effects of magnetic fields up to 20 T were studied in CuInSe2 single crystals using photoluminescence (PL) at 4.2 K. Diamagnetic shifts of the free A and B excitons measured in the PL spectra in CuInSe2 at 4.2 K tinder the magnetic fields were used to estimate the reduced masses (0.095m(0) for the A and 0.098m(0) for the B exciton), binding energies (7.0 meV for the A and 7.2 meV for the B exciton) and Bohr radii (7.6 nm for the A and 7.3 nm for the B exciton) of the free-excitons in CuInSe2 assuming that both excitons are isotropic and hydrogen-like. (C) 2009 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim},
    editor = {S Sadewasser and D AbouRas and B Lake and HW Schock},
    keywords = {optical-properties, energy, constant, single-crystals, Physics, Condensed Matter Physics},
    url = {http://strathprints.strath.ac.uk/37429/}
    }

  • H. Zachmann, S. Heinker, A. Braun, A. V. Mudryi, V. F. Gremenok, A. V. Ivaniukovich, and M. V. Yakushev, “Characterisation of Cu(In,Ga)Se₂-based thin film solar cells on polyimide,” Thin Solid Films, vol. 517, iss. 7, p. 2209–2212, 2009.
    [BibTeX] [Abstract] [Download PDF]

    Thin films of Cu(In,Ga)Se2 (CIGS) were deposited at temperatures below 450 ?C on polyimide (PI) substrates coated with Mo in a roll-to-roll set up by a combination of co-evaporation and ion-beam techniques. Flexible solar cells ITO/i-ZnO/CdS/CIGS/Mo/PI with and without Na incorporation were then fabricated. The films and solar cells were examined by: X-ray fluorescence spectroscopy (XRF) and Auger electron spectroscopy (AES), to determine the elemental composition, as well as by X-ray diffraction for structure- and scanning electron microscopy (SEM) for morphology-analysis. Photoluminescence (PL) and PL-excitation (PLE) at temperatures from 4.2 to 78 K were also used to estimate the band-gap energy of CIGS, examine the electronic properties and defect nature. The aim of this study was to correlate the incorporation of Na with optical and structural parameters of the CIGS layers as well as with the solar cell performance.

    @Article{strathprints19251,
    author = {H. Zachmann and S. Heinker and A. Braun and A.V. Mudryi and V.F. Gremenok and A.V. Ivaniukovich and M.V. Yakushev},
    title = {Characterisation of Cu(In,Ga)Se₂-based thin film solar cells on polyimide},
    journal = {Thin Solid Films},
    year = {2009},
    volume = {517},
    number = {7},
    pages = {2209--2212},
    month = {February},
    abstract = {Thin films of Cu(In,Ga)Se2 (CIGS) were deposited at temperatures below 450 ?C on polyimide (PI) substrates coated with Mo in a roll-to-roll set up by a combination of co-evaporation and ion-beam techniques. Flexible solar cells ITO/i-ZnO/CdS/CIGS/Mo/PI with and without Na incorporation were then fabricated. The films and solar cells were examined by: X-ray fluorescence spectroscopy (XRF) and Auger electron spectroscopy (AES), to determine the elemental composition, as well as by X-ray diffraction for structure- and scanning electron microscopy (SEM) for morphology-analysis. Photoluminescence (PL) and PL-excitation (PLE) at temperatures from 4.2 to 78 K were also used to estimate the band-gap energy of CIGS, examine the electronic properties and defect nature. The aim of this study was to correlate the incorporation of Na with optical and structural parameters of the CIGS layers as well as with the solar cell performance.},
    keywords = {Cu(In, Ga)Se-2, solar cells, polyimide, photoluminescence, characterisation, thin solar cells, Physics, Materials Chemistry, Surfaces and Interfaces, Electronic, Optical and Magnetic Materials, Surfaces, Coatings and Films, Metals and Alloys},
    url = {http://strathprints.strath.ac.uk/19251/}
    }

  • M. V. Yakushev, R. W. Martin, and A. V. Mudryi, “Diamagnetic shifts of free excitons in CuInS₂ in magnetic fields,” Applied Physics Letters, vol. 94, iss. 4, p. 42109, 2009.
    [BibTeX] [Abstract] [Download PDF]

    Single crystals of CuInS2 were studied with reflectance (RF) and photoluminescence (PL) at 4.2 K in magnetic fields up to 10 T. The diamagnetic energy shifts observed for the free excitonic lines in both the RF and PL spectra were used to calculate the reduced masses (0.141m0, 0.142m0, and 0.114m0), binding energies (18.46, 18.59, and 14.90 meV), Bohr radii (3.82, 3.79, and 4.73 nm), and hole effective masses (1.20m0, 1.28m0, and 0.40m0) for the ALPB, AUPB, and BC excitons, respectively, using a low-field perturbation approach.

    @Article{strathprints19311,
    author = {M.V. Yakushev and R.W. Martin and A.V. Mudryi},
    title = {Diamagnetic shifts of free excitons in CuInS₂ in magnetic fields},
    journal = {Applied Physics Letters},
    year = {2009},
    volume = {94},
    number = {4},
    pages = {042109},
    month = {January},
    abstract = {Single crystals of CuInS2 were studied with reflectance (RF) and photoluminescence (PL) at 4.2 K in magnetic fields up to 10 T. The diamagnetic energy shifts observed for the free excitonic lines in both the RF and PL spectra were used to calculate the reduced masses (0.141m0, 0.142m0, and 0.114m0), binding energies (18.46, 18.59, and 14.90 meV), Bohr radii (3.82, 3.79, and 4.73 nm), and hole effective masses (1.20m0, 1.28m0, and 0.40m0) for the ALPB, AUPB, and BC excitons, respectively, using a low-field perturbation approach.},
    keywords = {binding energy, copper compounds, diamagnetic materials, effective mass, excitons, indium compounds, photoluminescence, reflectivity, ternary semiconductors, Physics, Physics and Astronomy (miscellaneous)},
    url = {http://strathprints.strath.ac.uk/19311/}
    }

  • M. V. Yakushev, R. W. Martin, and A. V. Mudryi, “Temperature dependence of excitonic emission in CuInSe₂,” Physica Status Solidi C, vol. 6, iss. 5, p. 1082–1085, 2009.
    [BibTeX] [Abstract] [Download PDF]

    Radiative recombination processes in CuInSe2 (CIS) single crystals grown by the, vertical Bridgman technique were studied using photoluminescence (PL) and reflectance (RF) spectroscopies at temperatures from 4.2 to 60 K, and excitation intensity from 0.6 to 30 W/cm(2). Study of the quenching parameters of the A and B freeo and first three bound-excitons (M1, M2 and M3) in high-quality CuInSe2 single crystal leads to estimates for the binding energy of the A (7.7 meV) and B (7.9 meV) free excitons as well as dissociation energies for the M1, M2 and M3 bound-excitons.

    @Article{strathprints37428,
    author = {M. V. Yakushev and R. W. Martin and A. V. Mudryi},
    title = {Temperature dependence of excitonic emission in CuInSe₂},
    journal = {Physica Status Solidi C},
    year = {2009},
    volume = {6},
    number = {5},
    pages = {1082--1085},
    note = {Special Issue: 16th International Conference on Ternary and Multinary Compounds (ICTMC16)},
    abstract = {Radiative recombination processes in CuInSe2 (CIS) single crystals grown by the, vertical Bridgman technique were studied using photoluminescence (PL) and reflectance (RF) spectroscopies at temperatures from 4.2 to 60 K, and excitation intensity from 0.6 to 30 W/cm(2). Study of the quenching parameters of the A and B freeo and first three bound-excitons (M1, M2 and M3) in high-quality CuInSe2 single crystal leads to estimates for the binding energy of the A (7.7 meV) and B (7.9 meV) free excitons as well as dissociation energies for the M1, M2 and M3 bound-excitons.},
    editor = {S Sadewasser and D AbouRas and B Lake and HW Schock},
    keywords = {single-crystals, photoluminescence , defect physics, optical-properties , chalcopyrite semiconductor, Physics, Condensed Matter Physics},
    url = {http://strathprints.strath.ac.uk/37428/}
    }

  • M. V. Yakushev, R. W. Martin, A. V. Mudryi, and A. V. Ivaniukovich, “Excited states of the A free exciton in CuInS₂,” Applied Physics Letters, vol. 92, iss. 11, p. 111908, 2008.
    [BibTeX] [Abstract] [Download PDF]

    {High quality CuInS2 single crystals, grown by the traveling heater method in an indium solvent, were studied using reflectance and photoluminescence at 4.2 K. The first

    @Article{strathprints19747,
    author = {M.V. Yakushev and R.W. Martin and A.V. Mudryi and A.V. Ivaniukovich},
    title = {Excited states of the A free exciton in CuInS₂},
    journal = {Applied Physics Letters},
    year = {2008},
    volume = {92},
    number = {11},
    pages = {111908},
    month = {March},
    abstract = {High quality CuInS2 single crystals, grown by the traveling heater method in an indium solvent, were studied using reflectance and photoluminescence at 4.2 K. The first, EAn=2=1.5494 eV, and second, EAn=3=1.5532 eV, excited states of the A free exciton have been observed in the photoluminescence spectra. Accurate values of the A exciton binding energy EFE A =18.5 meV and Bohr radius aB A=3.8 nm, bandgap Eg=1.5540 eV at 4.2 K and static dielectric constant =10.2 have been derived assuming a hydrogenic model.},
    keywords = {exciton, CuInS2, crystals, Physics, Physics and Astronomy (miscellaneous)},
    url = {http://strathprints.strath.ac.uk/19747/}
    }

  • A. V. Mudryi, A. V. Ivanyukovich, M. V. Yakushev, R. Martin, and A. Saad, “Optical spectroscopy of free excitons in a CuInS₂ chalcopyrite semiconductor compound,” Semiconductors, vol. 42, iss. 1, p. 29–33, 2008.
    [BibTeX] [Abstract] [Download PDF]

    The spectra of reflectance and luminescence of high-quality CuInS2 single crystals grown by oriented crystallization are studied at the temperature 4.2 K. In the region of the fundamental absorption edge, the two excitonic resonance reflectance peaks, nondegenerate peak A at the energy {$\sim$}1.5356 eV and doubly degenerate peak BC at the energy {$\sim$}1.5567 eV, and the luminescence signal produced by free and bound excitons are observed. The luminescence lines, A UPB at {$\sim$}1.5361 eV and A LPB at {$\sim$}1.5347 eV, with a half-width {$\sim$}1 meV, are attributed to exciton-polariton recombination. From the experimentally observed energy position of the exciton ground state and excited states, the binding energy of free excitons is determined to be {$\sim$}18.5 meV. In studying the photoluminescence in magnetic fields up to 10 T, a diamagnetic shift of the ground state of free excitons A is observed.

    @Article{strathprints19828,
    author = {A.V. Mudryi and A.V. Ivanyukovich and M.V. Yakushev and Robert Martin and A. Saad},
    title = {Optical spectroscopy of free excitons in a CuInS₂ chalcopyrite semiconductor compound},
    journal = {Semiconductors},
    year = {2008},
    volume = {42},
    number = {1},
    pages = {29--33},
    month = {January},
    abstract = {The spectra of reflectance and luminescence of high-quality CuInS2 single crystals grown by oriented crystallization are studied at the temperature 4.2 K. In the region of the fundamental absorption edge, the two excitonic resonance reflectance peaks, nondegenerate peak A at the energy {$\sim$}1.5356 eV and doubly degenerate peak BC at the energy {$\sim$}1.5567 eV, and the luminescence signal produced by free and bound excitons are observed. The luminescence lines, A UPB at {$\sim$}1.5361 eV and A LPB at {$\sim$}1.5347 eV, with a half-width {$\sim$}1 meV, are attributed to exciton-polariton recombination. From the experimentally observed energy position of the exciton ground state and excited states, the binding energy of free excitons is determined to be {$\sim$}18.5 meV. In studying the photoluminescence in magnetic fields up to 10 T, a diamagnetic shift of the ground state of free excitons A is observed.},
    keywords = {cuInS2, optical spectroscopy, crystals, Physics, Atomic and Molecular Physics, and Optics, Electronic, Optical and Magnetic Materials, Condensed Matter Physics},
    url = {http://strathprints.strath.ac.uk/19828/}
    }