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Thin films of Cu(In,Ga)Se2 on Mo coated glass substrates were studied by photoluminescence (PL) technique before and after irradiation in liquid nitrogen bath with a dose of 1.8 x 1015 cm−2 of 10 MeV electrons to determine the nature of radiation defects in Cu(In,Ga)Se2. The PL spectra before irradiation contain a broad dominant band at 1 eV, consisting of 3 peaks P1, P2 and P3, and two low intensity bands P4 at 0.86 eV and P5 at 0.77 eV. Because of their strong j-shift the P1, P2 and P3 were assigned to the free-to-bound (FB) recombination of free electrons and holes localised at 3 different acceptors whose energy levels are affected by potential fluctuations of the valence band. The P4 and P5 bands were also assigned to the FB recombinations of free electrons but with deeper acceptors. Irradiation reduced the PL intensity of the dominant 3 bands P1, P2 and P3. We assign such a reduction to the formation of nonradiative defects acting as deep traps. Irradiation did not change the j-shift of the P3 band (12 meV/d) suggesting that the acceptor, associated with P3, was not affected by irradiation. However, irradiation reduced the P2 j-shift from 13.8 meV/d to 4 meV/d demonstrating a significant reduction of the compensation level associated with this acceptor. Warming to the room temperature doubled the intensity of the dominant band probably due to annealing of some radiation induced defects. It increased the P2 j-shift to 10 meV/d demonstrating rising compensation level associated with this acceptor.

Thin films of Cu2ZnSnSe4 (CZTSe) were fabricated by the selenisation of metallic precursors sequentially deposited on Mo coated glass substrates. The surface morphology and cross section, studied by a scanning electron microscope (SEM), reveal densely packed grains with sizes in excess of 1 µm and CZTSe film with a thickness of 1.4 µm. The elemental composition of both the precursors and CZTSe films was measured by an energy dispersive X-ray analyser demonstrated a copper deficiency and zinc excess as well as a near stoichiometric content of Se. A set of 4 as deposited CZTSe films was used to produce solar cells with the structure ZnO/CdS/Cu2ZnSnSe4/Mo/glass. These films were coated with CdS buffer layer using a standard chemical bath deposition after chemical etching using KCN or/and ammonia: film E was not etched, film B was etched in KCN for 2 minutes, film C was etched in KCN for 5 minutes and film D was etched in KCN for 30s and then in ammonia for 5 minutes. Solar cells were then completed by DC-magnetron deposition of ZnO/ZnO:Al transparent front contacts. Finally solar cells with areas of 3x3 mm2 were separated by mechanical scribing. The structural properties of the cells and phase content of the CZTSe layer were examined by x-ray diffraction (XRD). Low intensity reflexes of the secondary phases SnSe and SnSe2 were also present. The bandgaps Eg of the CZTSe layers in the cells, measured by photoluminescence excitation (PLE) at 4.2 K, were found to be of 1.05 eV in all the four cells. This cell also showed the highest FF of 41.1% whereas the best Isc of 46.6 mA/cm2, demonstrated by the D cell. The highest conversion efficiency of 6.2% was obtained for the E cell, produced without any etch, and for the D one after 30 s etch in KCN plus 5 minutes in ammonia.

Transition-metal-doped semiconductor GaAs crystals are used as model systems for spintronic research, as well as in other applications. To explore the structure and properties of such impurities, we extended the methodology of ultrasonic investigation of the Jahn-Teller effect in dielectric impurity-centers to the study of significantly different semiconductor impurities using the GaAs:Cu crystal as an example. Phase velocity and attenuation of ultrasound in this system were measured in the temperature interval of 1.9-80 K at 52 MHz and 156 MHz. The anomaly in the velocity and a peak of attenuation found for the longitudinal and slow shear waves indicate the presence of the Jahn-Teller effect with the e-type local distortions of the CuGa4As impurity complex. The temperature dependence of the elastic modulus and relaxation time shows that below 5 K, the thermal activation mechanism of relaxation is possibly replaced by resonance type transitions. The main parameters of the Jahn-Teller effect, stabilization energy, minima positions and the barrier between them, frequency of pseudorotation of the distortions, and the tunneling splitting of the ground state energy, as well as the constant of exchange interaction between the two holes in Cu2+ centers and the concentration of the centers were estimated. © 2014 AIP Publishing LLC. Russian Foundation for Basic Research, RFBR