Optical properties and band structure of chalcopyrite materials CuGaxIn1-xS2

The work is devoted to the investigation of chalcopyrite monocrystals CuGaxIn1-xS2 by means of optical and Raman spectroscopy with high resolution at helium and room temperatures. It was determined the ground and excited states of long-wave A exciton (series Γ4 and Γ5), the ground and excited states of short-wave Β(Γ5) and C(Γ4) series, the parameters of excitons and band structure ( Eg, ΓCF, ΓSO), the electron and hole effective masses, the influence of a solid solution on the main exciton parameters and band structure. The upper and lower branches of the exciton polaritons Γ4 and Γ5 in the 'bottle neck' region were determined. It is established, that an anisotropy of translational masses takes place, longitudinal masses is less than transversal masses of excitons Γ4. It was found from experimental results and calculations of optical spectra that the electron effective masses in the conduction band increased linearly during the reduction X in structures CuGaxIn1-xS2 from 0.12 m 0 to 0.23 m 0. Effective mass of the upper valence band (symmetry Γ6) increased with a higher gradient, than effective masses (B series, Γ 7 band) and (C series, Γ 6 band). It is shown, that exciton Γ4 creates additional polaritons waves of excitons Γ5, which interfering, defining thin structure of optical spectra of exciton resonance. The polariton branches and the translational masses of Γ5 excitons were determined. It was shown, that takes place a conversion of energy between polaritons branches, which is found out in absorption and luminescence spectra. It is analyzed resonant Raman scattering of energy of exciton polaritons in compounds CuGaxIn1-xS2. Scattering of energy occurs as multiphonon process of radiation with participation of phonons 1LO, 2LO, 3LO. In considered crystals, during scattering of phonons 1LO and 2LO arrange by increasing of energy. The scheme of a cascade relaxation of energy polaritons on 1LO and 2LO phonons is offered. Resonant character of dispersion with change of structure of solid solutions is revealed, as result of approach exciton polaritons levels to excitation lines. The pre resonant condition is investigated and established, that intensity of a scattering line of phonons 1LO and 2LO increases then the energy approaches the excitation resonant frequency (Ej - Eg). The obtained results have been published in 15 scientific works. (author)