S. Evtimova

Studies of the phase equilibria in the Ag-Sn-Zn system

Abstract The isothermal section of the equilibrium phase diagram Ag–Sn–Zn has been constructed at 380°C using optical and scanning electron microscopy, X-ray analyses, microhardness measurements and differential scanning calorimetry. The ternary β phase (solid solution range of the binary AgZn β phase) contains up to ≈13 at.% Sn, the ϵ phase about 0.2 at.% Sn. The solubility of Zn in the Ag–Sn-based intermetallic phases is determined for the first time. The microhardness of the γ phase (≈450 MPa) is the highest in the system Ag–Sn–Zn. A linear dependence of the microhardness versus mol fraction of silver has been revealed for the ϵ phase.

Experimental study of the ternary Ag–Sn–Zn system through diffusion couples

Abstract The phase boundaries of the ternary Ag–Sn–Zn system have been verified using diffusion couples. Concentration and microhardness profiles of the diffusion zone have been constructed. Solid state precipitations at room temperature have been observed in the binary AgSn F.C.C. solutions as well as in the ternary intermediate compounds. The tin solubility in the silver is less than expected according to the pertinent binary phase diagram. Growth coefficients of the intermediate phase layers (for the ternary β, γ, ϵ phases) have been assessed.

Free electron recombination in degenerately doped and moderately compensated gallium arsenide

The room-temperature, band-edge photoluminescence spectra of degenerately doped (n=1, 2, 3, 8, 10*1019 cm-3) and compensated (K=0.05, 0.1, 0.2, 0.3, 0.5) samples have been investigated for identification of the radiative recombination mechanism and to analyse the possibility for a quantitative estimation of the Burstein-Moss shift. The measured spectra consist of two emission bands. The high-energy band (band-edge luminescence) predominates in intensity over the impurity-associated emission band. The spectral shape is discussed in accordance with theoretical ideas that it follows the free electron energy distribution. The calculated curves (over the full range of electron concentration) are in good agreement with the experimental spectra.

Electron mobility in heavily doped and compensated gallium arsenide due to scattering by potential fluctuations

The electron mobility at 77K of heavily doped and compensated gallium arsenide is calculate assuming the predominant scattering comes from a smooth random potential due to a large number of charged impurities with correlated impurity distribution. The nonparabolicity of a conduction band is taken into account at large electron concentrations. A set of samples with given compensation ratios and electron concentrations has been used for experimental verification of the model which explains well the experimental mobilities.

Magnetic-field-induced localization of electrons in InGaN/GaN multiple quantum wells

We study longitudinal electron transport in InGaN/GaN multiple quantum wells (MQWs) at moderate magnetic fields. We observe a stepwise behavior of both the Hall coefficient and magnetoresistivity. The peculiarities are explained by a magnetic-field-induced localization of electrons in a two-dimensional (2D) potential relief of the InGaN MQW due to composition fluctuations. We extend the model for a magnetic localization of electrons, treating every QW like a quasi-2D system with a cylindrical potential relief. The calculated values of the decrease of the sheet electron concentrations in a magnetic field based on such an assumption for 2D density of states in a InGaN MQW system are in good accordance with the experimentally obtained values.

Sublinear impurity solubility in indium phosphide and gallium arsenide epitaxial layers

Abstract The solubility curves of tellurium donors in InP and GaAs liquid phase epitaxial layers, as well as germanium and zinc acceptors in GaAs and InP, respectively, are studied on the basis of impurity and native defect equilibria. In a wide doping range our results are in good accordance with calculated solubility dependences. The influence of vacancies in both sublattices on the impurity incorporation is taken into account. As a result, a sublinear donor and nearly linear acceptor solubility occurs, depending on the vacancy-to-impurity concentration ratio.

ELECTRON TRANSPORT IN SB-DOPED METALORGANIC EPITAXIAL GAAS GROWN AT MODERATE AS-RICH CONDITIONS

The influence of antimony incorporation in GaAs metalorganic vapor phase epitaxial (MOVPE) layers has been investigated. The results obtained concern the behavior of the carrier concentration (n) and the mobility (μ) developed from Hall effect measurements. In order to achieve a reliable quantitative interpretation the samples studied have been grown at a moderate V/III ratio which ensures n‐type conductivity and does not favor SbGa heteroantisite defect formation. Three regions of specific influence of Sb doping on the electrical parameters have been distinguished. For Sb mole fraction in the input gas phase (MFTMSb) ranging between 0 and 6×10−6, n slightly decreases, while the mobility sharply increases compared with undoped layers. This is discussed in terms of electrically active and neutral As vacancies. The quantitative consideration of the scattering mechanism offers the possibility of correcting the compensation ratio in the undoped GaAs samples determined by commonly used procedures. The n and μ ...

Investigation of ZrN Hard Coatings Obtained by Cathodic Arc Evaporation

Zirconium nitrides (ZrN) coatings have shown better quality in comparison to titanium nitrides (TiN) ones regarding the application in the mechanical processing of aluminum and titanium alloys. This work presents the results from investigation on properties of ZrN-based coatings intended for industrial application. The ZrN and ZrTiN hard coatings in a thickness of (3 5) m were obtained on stainless steel substrates by cathodic arc evaporation method. The coating hardness in the range of 25-32 GPa was evaluated using the Vickers measurement technique. The coating properties were studied in relation to the surface morphology by Atomic force microscopy (AFM) and Scanning electron microscopy (SEM). The analyses showed that the number and size of the macroparticles decrease when N2 pressure increases in the deposition chamber. X-ray diffraction analysis (XRD) was performed to identify the crystallographic structure, preferred orientation and stress of the ZrN coatings.

Effect of carrier concentration on the microhardness of GaN layers

The paper presents a microhardness study of thick crack-free hydride vapor phase epitaxial GaN layers (not intentionally doped), and of thin metal-organic vapor phase epitaxial (MOVPE) GaN layers (undoped and Si-doped), grown on sapphire. A Vickers indentation method was used to determine the microhardness under applied loads up to 2 N. An increase in the microhardness was observed with decreasing carrier concentration and increasing mobility. A dip at an indentation depth of about 0.75 μm is observed in the microhardness profile in the MOVPE films, and is correlated with peculiarities in the spatially resolved cathodoluminescence spectra. The relationship between the mechanical and electrophysical parameters is discussed.

Hall effect data analysis of GaN n(+)n structures

We develop a model for analysis of Hall effect data of GaN structures composed of sublayers with different thicknesses and contacts placed on the top surface, We analysed the contributions of the c ...