I. V. Semkiv

This work presents the ab initio calculations of the electronic energy spectrum of the In4CdI6 compound. The study was conducted within the framework of density functional theory (DFT), using local density approximation (LDA) and general gradient approximation (GGA) pseudopotentials, and the Heyd–Scuseria–Ernzerhof (HSE06) hybrid functional. The GGA approximation was implemented using the PBE and PBEsol exchange-correlation functional. Based on the electronic energy structure, the type of the minimum band gap was determined, and an analysis of the energy level dispersion for both the valence and conduction bands was performed. Furthermore, the effective masses of electrons (mc) and holes (mν) for In4CdI6 were established. The energy band analysis was complemented by the calculation of the density of states (DOS). Based on the electronic energy spectrum, the real and imaginary components of the dielectric function are calculated. Using the Kramers–Kronig relations, we also derive such fundamental optical functions of In4CdI6 as the refractive index n, and the extinction coefficient k.

The results of an investigation of the optical and electrical properties of GaAs and Al _0.1 Ga _0.9 As epitaxial films are presented. Furthermore, the effects of Yb and Te doping on optical and electronic characteristics were examined. The charge carrier concentration ( n _e ) was determined based on Hall effect measurements. All the synthesized films exhibited n -type conductivity. The optical transmittance and reflectance spectra were measured in the visible and near-infrared regions (350-1600 nm). From these results, the key energy parameters, namely the band gap ( E _g ) and Urbach ( E _U ) energy, were established. Using the Kramers-Kronig relations, the spectral behaviour of the fundamental optical functions, including the absorption coefficient (α), extinction coefficient ( k ), refractive index ( n ), and the real (ε ₁ ) and imaginary (ε ₂ ) parts of the dielectric function, was determined. The dispersion of the refractive index is discussed in terms of the Wemple and Di Domenico single oscillator model. A comprehensive analysis of their spectral behaviour was conducted, followed by a comparison of the established values with reference data. The findings of this study conclude with a discussion of the potential practical applications of the investigated compounds.

This work presents the results of a study on the electronic energy structure of La-doped gallium arsenide (GaAs). The electronic energy spectrum was calculated within the framework of density functional theory. Furthermore, the concentration dependence of the main energy and optical properties of Ga _{1− x} La _x As was established for La concentrations ranging from x = 0 to 0.25. An analysis of the energy band dispersion and density of states was performed. Based on the electronic energy spectrum, the real and imaginary components of the dielectric function were calculated for the studied samples. Using the Kramers–Kronig relations, fundamental optical functions, such as the refractive index ( n ), extinction coefficient ( k ), and absorption coefficient ( α ) were derived. The concentration dependence of these optical functions was established, followed by a comparative analysis with existing literature data.

This study investigates the compound CdI2, which is actively used as a component in scintillation detectors for the detection of alpha-particle radiation. The research addresses the task to correlate experimental results with theoretically determined parameters of CdI2 films. One of the primary objectives for studying this compound is to determine its electronic structure and optical properties. The CdI2 thick film was obtained by cleaving from a bulk sample. The average thickness of the CdI2 thick film is 2 μm. The optical properties of CdI2 thick film were investigated by optical absorption spectra. The absorption spectrum fitting method was applied to estimate the optical band gap and Urbach energy of the CdI2 thick film. This method requires only the measurement of the absorbance spectrum, and no additional information, such as the film thickness or reflectance spectra. The optical band gaps and Urbach energy obtained for the CdI2 thick film are 3.05 eV and 5.17 eV, respectively. Electronic band structure and energy properties were studied for CdI2. We calculated the electron dispersion at high symmetry directions of the Brillouin zone and density of electron estimated with the generalized gradient approximation (GGA). A Perdew–Burke–Ernzerhof functional for solids (PBEsol) was applied. Based on the dispersion of energy bands, the predominant type of conductivity in the studied materials was determined. Consistency of theoretical and experimental parameters exceeds that reported in previous studies, which supports the use of CdI2 as a model compound, especially in the search and design of novel crystalline materials. The established parameters could be used in the development of components for a scintillation detector

CdSe1-xSx (x = 0, 0.3, 0.4, 0.6, and 1) thin films were deposited on a quartz and silicon substrate using high-frequency magnetron sputtering. X-ray diffraction analysis estimated that the CdSe1-xSx thin films are crystallized in a hexagonal structure [structure type – ZnO, space group P63mc (No. 186)]. Spectral dependence of the optical transmittance between 300 and 1500 nm of the obtained thin films at room temperature was measured. Normalized integral optical transmittance, optical band gap, spin-orbit splitting, and the value of the bowing parameter of the CdSe1-xSx thin films are determined. The values of the optical band gaps for CdSe1-xSx thin films were estimated using the two methods (by Tauc plot and dT/dλ). Concentration dependences of the energy gaps connected with the leading optical transitions in CdSe1-xSx (Г8v–Г6c, Г7v–Г6c) and spin-orbit splitting are studied. It is shown that the concentration dependences of main optical transitions are quadratic. The principal explanation for this seems to be the Burstein–Moss effect, which is caused by the doping atoms' excess carriers (electrons and holes).