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CNAA / Theses / 2016 / June /

Optical properties and energy band structure of crystals CdGa2S(Se)4, PbGa2S4, AgAsS2


Author: Parvan Vladimir
Degree:doctor of physics and mathematics
Speciality: 01.04.10 - Semiconductors physics and engineering
Year:2016
Scientific adviser: Nicolae Sîrbu
doctor habilitat, professor, Technical University of Moldova
Scientific consultant: Veaceslav Ursachi
doctor habilitat, associate professor (docent), Institute of Applied Physics of the ASM
Institution: Technical University of Moldova

Status

The thesis was presented on the 23 June, 2016
Approved by NCAA on the 6 October, 2016

Abstract

Adobe PDF document1.95 Mb / in romanian

Thesis

CZU 621.315.592

Adobe PDF document 11.41 Mb / in romanian
150 pages


Keywords

birefringence, spatial dispersion, optical properties, exciton, polariton, energy band structure, reflection spectra modulated by wavelength, parameters of the exciton states, exciton Rydberg constant, refractive index, isotropic point, extinction coefficient, real and imaginary part of the dielectric constant, effective mass of electrons and holes, reduced and translational mass of the exciton

Summary

The thesis is written in Romanian language and includes an introduction, three chapters, general conclusions, one annexe and a list of 141 cited publications. The thesis consists of 150 text pages, 113 figures, 18 tables and 68 formulas.

The thesis is dedicated to: 1. Investigate the phenomenon of birefringence in materials CdGa2S(Se)4, PbGa2S4, AgAsS2 and identify potential opportunities to create devices based on the studied materials. 2. Study of the exciton states, which provide more complete information about the basic phenomena of propagation of light waves in crystals, the input and output of the radiation in the crystal, which define the parameters of optoelectronic devices. 3. Research of the absorption spectra in the region of the fundamental absorption. Definition of the energy bands structure of the same series of crystals, which has perspectives for use in various optoelectronic devices. Including as the absorber layer in solar energy converters.

The main objective of this work was complex study of fundamental properties of CdGa2S(Se)4, PbGa2S4, AgAsS2; their optical parameters n, k, ε1, ε2; parameters of the exciton states R, Eg, M, μ, εb, mc, mv, ωLT, Δcf, Δso, and determination of the energy bands responsible for the transitions in the depth of main absorption band.

This work presents for the first time exciton states n = 1, 2, and 3 of Frenkel and Wannier–Mott exciton in the crystal PbGa2S4 for the rest of crystals were determined states n = 1, 2, and 3 of Wannier–Mott exciton, were analyzed spectra parameters and were performed calculations of exciton states in these materials and determined the structure of energy bands.

As a result of this work have been resolved following scientific problems: the study of the anisotropy of the optical properties in the beginning of the absorption edge, defined dependence of refractive index from polarization and the direction of the wave vector and identified the isotropic wavelength (λ0). Was studied polarization dependence of exciton spectra. Were made theoretical calculations by dispersion relations of polarized spectra of Frenkel excitons and Wannier–Mott, were calculated optical functions (n, k, ε1, ε2) by the Kramers–Kronig relations. The results of this study are of interest for fundamental physics and materials science of ternary compounds and uniaxial and biaxial crystals. The results are published in 15 scientific papers in journals at home and abroad, 6 of which were published in journals with impact factor. Were obtained two silver medals at international exhibitions and diploma of excellence. Was obtained nominal scholarship "Sergei Redeutsanu" for doctoral students, provided by the Government of the Republic of Moldova.