StatusThe thesis was presented on the 2 September, 2011
Approved by NCAA on the 5 October, 2011
Abstract– 0.58 Mb / in romanian
– 0.58 Mb / in russian
The thesis is related to the investigation of optical properties of Cu(In1-xGax)3Se5 and Cu(In1-xGax)5Se8, CuIn1-xGaxSe2 and Cu2ZnSnS4 and Cu2ZnGeSe4, materials promising for engeneering of various optoelectronic devices, including high-performance, low-cost solar energy converters on their basis .
The main purpose of this study was to determine their optical functions (the refractive index, extinction coefficient, absorption coefficient, reflection coefficient, and dielectric constant).
This work is the first systematic study of optical properties of solid solutions Cu (In1-xGax)1+2nSe2+3n for n = 1, 2 and Cu2ZnSnS4 and Cu2ZnGeS4.
The main scientifical problem resolved by the thesis is: the band structure of Cu(In1-xGax)3Se5 and Cu(In1-xGax)5Se8, Cu2ZnSnS4 and Cu2ZnGeS4 crystals was determined in the region of band gap and higher transitions by spectroscopic ellipsometry and the dependences of the dielectric functions, rexractive index, extinction, absorbtion and reflexion coefficients for the first time.
Spectral dependences of dielectric function, refractive index, extinction, absorption and reflection coefficients were determined, using a two phase model (atmosphere-sample), over the energy range from 0.8 to 4.7 eV for Cu(In1-хGaх)3Se5 and Cu(In1-хGaх)5Se8 solid solutions and for Cu2ZnSnS4, and over the energy range from 1.4 to 4.7 eV for Cu2ZnGeS4. The spectral dependences of extinction coefficient and refractive index for Cu(In1-XGaX)Se2 thin films were obtained from transmittance and reflectance at normal incidence data, measured in the range from 300 to 1500 nm.
The Adachi’s model parameters were determined by simultaneous modeling of real and imaginary parts of dielectric function using Simulated Annealing algorithm (SA), and by fitting of the second derivative of the experimental spectrum to the analytical lines for Cu(In1-хGaх)3Se5 and Cu(In1-хGaх)5Se8 solid solutions, and for Cu2ZnSnS4 and Cu2ZnGeS4; a good agreement with the experimental data was obtained.
The extinction spectra structure of CuInSe2 was analyzed using the Adachi model and simulated annealing algorithm (SA). The absorption edge was analyzed by model for semiconductors with band gap fluctuations. The band gap values for Cu(In1-XGaX)Se2 for different x were obtained from extrapolation of absorption coefficient extrapolation and their concentration dependence was determined.
Results obtained in the thesis are of interest for physics and materials science of ordered vacancy compound and kesterite materials.
The thesis is written in Russian and includes an introduction, four chapters, general conclusions, two annexes and a list of cited papers. The thesis consists of 115 text pages, 57 figures, 15 tables and the list of cited papers includes 114 references.
The obtained results were published in 22 scientific papers (9 articles and 13 abstracts).