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GaSe and InSe nanolayers were obtained by mechanical exfoliation and physical vapor deposition methods on silicon substrates. Employing atomic force microscopy the surface morphology and thickness of obtained InSe and GaSe nanolayers were studied, as well as their temporal stability. The observed spectral positions of the Raman peaks were in agreement with the positions of the peaks known for bulk and nanolayered InSe and GaSe samples.

A procedure for the synthesis of a CdSiP2 compound from the initial elementary components in a gradient thermal field has been developed. The phase and chemical composition of the synthesized and recrystallized material is confirmed by the data of X-ray diffraction analysis and scanning electron microscopy with an energy-dispersive system. The polycrystalline material obtained by the developed method will be used to grow bulk nonlinear optical CdSiP2 crystals.

Terahertz generation from the InP, InSb, GaAs and GaSe crystal surfaces excitated by femtosecond laser pulses has been studied. The terahertz spectra emitted from the native crystals and the crystals previously irradiated by high-energy neutrons or electrons have been recorded. Also, a simulation of the terahertz emission process has been performed. A weak terahertz signal generated from the GaSe native surface has been registered. In the case of electron-irradiated GaSe, the signal is increased several fold because of increased laser radiation absorption.

The process of GaSe native oxide formation was studied using atomic-force microscopy. It was found that the oxide film growth is accompanied by a work function increase. This increase saturates in several hours. The illumination by 1 mW laser at 650 nm stimulates the oxidation process. Continuous illumination changes the work function by 1 eV and that is 2 times higher than that without irradiation. It is supposed that the oxide formation occurs at edge dislocation lines.

Thin amorphous SiO2, TiO2, and Ga2O3 films were deposited on the surface of GaSe crystals by thermal and magnetron sputtering. It was found that under different technological conditions, the SiO2 and TiO2 layers on the surface of GaSe crack, while the Ga2O3 compound forms perfect films. A comparison of the transmission spectra and generation efficiency of terahertz pulses was made for the SiO2-GaSe, TiO2-GaSe, and Ga2O3-GaSe structures and for the GaSe:S 0.9 wt % and GaSe:S 7 wt % crystals. It was found that an increase in the concentration of sulfur in the GaSe:S crystals results in a decrease in the efficiency of generation of terahertz radiation by optical rectification of femtosecond laser pulses. Among the films deposited on the surface of GaSe, the SiO2 film has the least impact on the efficiency of generation.

Theoretical estimates and experimental results of the study of the second harmonic oscillation in nonlinear GaSe and GaSe:S crystals excited by a 10.6-μm CO2 laser are presented. The measured second harmonic maximum radiation power and power conversion efficiency for GaSe crystals were 8 kW and 0.5%, respectively. Data on the damage thresholds for GaSe and GaSe0.7S0.3 crystals irradiated by a CO2 laser are presented.

A series of technological experiments on the growth of GaSe:Te single crystals by the Bridgman–Stockbarger method is performed. Surface micromorphology and mechanical properties of crystals with different doping levels are studied. Spectral dependences of the complex refractive index are obtained using ellipsometry. The experimental data are approximated within the Lorentz–Drude model.

The most probable parameters of the pure, doped, and mixed GaSe1−xSx (x ≤ 0.4) crystals (solid solutions) are presented together with the results of investigations of their crystal structure and defects, optical and mechanical properties, and damage thresholds.

Gallium selenide is a material with great potential for nonlinear optical applications, due to its many attractive properties, including a broad low-loss transmittance (from 0.65 to 18 μm) and a large nonlinear coefficient. However, its current application is limited due to difficulties with its growth, and poor mechanical properties. Our current research has a threefold purpose. First, this work is intended to investigate the feasability of growing large, optical quality single crystal boules of GaSe; second, to investigate the impact of isovalent indium doping on the mechanical, electrophysical, and optical properties of GaSe, and third, to determine the concentration of In which is optimal for purposes of facilitating the practical implementation of GaSe in nonlinear devices.

Research in doping processes of ternary chalcopyrites A 2 B 4 C 2 5 is of primary interest for several reasons. First of all, a study of the dependencies of ‘the properties of crystal vs. the concentration of impurity in melt’ decides a fundamental problem. It is a check on the theory of ordering of a crystal structure for some specifically defined values of dopant concentration leading to a possible phase transformation caused by the self-organization of large-scale fluctuations in a melt. On the other hand, it is necessary also for practical tasks—for example, obtaining high-resistance CdGeAs 2 -crystals for use in nonlinear optics. In the present work data on electrical activity and on an effect in the electrophysical properties of ternary semiconductors CdGeAs 2 and CdSnAs 2 are obtained for dopants of Au, Cu, Zn, In, Sc and Gd in CdGeAs 2 and for Au, Cu and In in CdSnAs 2 , added to a melt during synthesis or recrystallization of a material.

Terahertz wave generation through optical rectification of femtosecond laser pulses and its detection in GaSe and GaSe1−x S x crystals with a relatively low (x = 0.04) and high (x = 0.29) content of sulfur was studied. The decrease of terahertz generation and detection efficiency at an increase of sulfur content in GaSe1−x S x was observed. The phase-matching conditions for electro-optical sampling in GaSe and GaSe1−x S x crystals were analyzed. The arising possibility to achieve the narrowing of terahertz detection bandwidth using thicker GaSe crystals was experimentally confirmed.

Structure, defects, mechanical and optical properties of GaSe1-xSx, 0

This paper presents the results of investigation on influence of doping with sulfur and annealing in sulfur atmosphere on properties of promising nonlinear optical gallium selenide crystals, grown by the Bridgeman method from melts with content of sulfur 0.01-3 mass % and annealed in sulfur atmosphere.

This paper presents the results of investigations on the influence of sulfur doping on properties of gallium selenide crystals, grown by the Bridgman method from melts with sulfur content of 0.01–3 mass %, using the Hall effect, optical absorption, photoconductivity and microhardness measurements on GaSe: S. The results obtained are explained by assuming the formation of solid solutions of GaSxSe1−x and the presence of the competitive processes of point defects and structural disorder formation.

We present an investigation of the diffusion and melt doping of Cu in CdGeAs2. Cu was found to be an acceptor, its introduction in the melt allowed the controlled introduction of holes from ∼8·1016 cm-3 to ∼1·1018 cm -3. Introduction of Cu from the melt was also found to improve the homogeneity of the crystal. The saturation solubility of Cu introduced via diffusion doping was found to have an exponential dependence on the diffusion temperature, from 723 K to 873 K, obeying the equation N = N0 exp (- δH / kT) with the parameters N0 = 6.10+19 cm-3, δH = 0.3 eV, and k equal to Boltzman's constant. From 873 K to 923 K, the saturation solubility was found to decrease exponentially with temperature.

Experiments on annealing of CdGeAs2-, CdSnAs2- and ZnGeP2-crystals in the vapor of volatile constituents were carried out. Conductivity and Hall effect measurements were performed to characterize the modification of electrical properties, caused by the interaction of the crystal with the gas phase during annealing. Literature data and the results of the present work are discussed based on the results of a quasi-chemical analysis. This yielded that the results of annealing depends essentially on both the conditions of the experiment and the initial imperfection of the crystal. The most probable native structural defects becoming apparent under the annealing were the following: for CdSnAs2 - SnCd, VAs; for CdGeAs2 - VAs, VCd, CdGe, GeCd; for CdSiAs2 - SiAs, VAs ; for CdSiP2 - VCd, VP; for ZnGeP2 - ZnGe, GeZn, VZn, VP; and for ZnSnP2- ZnSn, SnZn, VZn, VP.

The quantity of material in vapour phase was defined by the weight-loss measurements. Two models of dissociation of CdGeAs2 and CdSnAs2 were considered. The models were based on condition of incongruent evaporation Model 1 and 2 called for absence or existence of Cd3As2 formation in gas phase. Corresponding sets of simultaneous equations were solved. The analyses of the results were carried out. An attempt to estimate the thermodynamic parameters of the compounds and values of total and partial equilibrium pressures at the melting point and lower temperatures was made.