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Optical properties and band structure of chalcopyrite materials CuGaxIn1-xS2

Author: Lucreţia Nemerenco
Degree:doctor of physics and mathematics
Speciality: 01.04.10 - Semiconductors physics and engineering
Scientific adviser: Nicolae Sîrbu
doctor habilitat, professor, Technical University of Moldova


The thesis was presented on the 22 October, 2007
Approved by NCAA on the 20 December, 2007


Adobe PDF document0.38 Mb / in romanian


CZU 621.315.592

Adobe PDF document 3.81 Mb / in romanian
177 pages


chalcopyrite materials, solid solution CuGaxIn1-xS2, spatial dispersion, optical propriety, exciton, polariton, energy band structure


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 Г4 and Г5), the ground and excited states of short-wave В(Г5) and С(Г4) series, the parameters of excitons and band structure ( Eg, ГCF, ГSO), 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 Г4 and Г5 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 Г4.

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 0.12m 0 to 0.23m 0. Effective mass of the upper valence band (symmetry Г6) increased with a higher gradient, than effective masses (B series, Г 7 band) and (C series, Г 6 band).

It is shown, that exciton Г4 creates additional polaritons waves of excitons Г5, which interfering, defining thin structure of optical spectra of exciton resonance. The polariton branches and the translational masses of Г5 excitons were determined. It was shown, that takes place a conversion of energy between polarotons 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 multifonon process of radiation with participation of fonons 1LO, 2LO, 3LO. In considered crystals, during scattering of fonons 1LO and 2LO arrange by increasing of energy. The scheme of a cascade relaxation of energy polaritons on 1LO and 2LO fonons 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 preresonant condition is investigated and established, that intensity of a scattering line of fonons 1LO and 2LO increases then the energy approaches hte excitation resonant frequency (Ej - Eg).

The obtained results have been published in 15 scientific works.

The thesis written in the Romanian language, contains 177 pages, 114 figures, 22 tables and 112 references.

The thesis is written in Romanian.