Temperature dependent Hall effect, magnetoresistivity and time resolved photoconductivity studies have been performed on GaN epilayers and GaN/InGaN multiple quantum wells (MQWs) grown on sapphire films by Metal Organic Chemical Vapor Deposition (MOCVD) method. The MQW structures consisted of different width or different amount of quantum wells. We related the electrical parameters with the quantum structure parameters and found that the geometrical variation of the quantum wells may be substituted by the variation of the amount of the quantum wells. The Hall and the magnetoresistivity measurements showed the complex behavior, which was attributed to the inhomogeneities of the samples, similarly to the case of the crystals with great size defects. copy 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

From magnetoresistivity effect measurements the carrier mobility at room temperature is found to be 200 cm(2) V-1 s(-1) in heteroepitaxially grown 3C-SiC on 6H-SiC by sublimation epitaxy. The main scattering mechanisms are found to be scattering by neutral impurities at low temperatures and by phonons at higher temperatures. The carrier concentration is in the range of 10(16) cm(-3), which corresponds to the concentration of residual doping by nitrogen acquired from photoluminescence measurements. Using magnetoresistance and Hall mobility data we have created a simple model which quantifies the volume of the samples influenced by extended defects. A higher doping near extended defects is either not present in the samples or might be screened by the electrostatic field created by these defects.

Thin films in the Mo-B-C system with varying carbon content (up to 37 at.%) were deposited using non-reactive DC magnetron sputtering. The phase composition and microstructure were determined and the potential use of the films in sliding electrical contact applications was evaluated. Films with lower than 23 at.% carbon content consisted of nanocrystalline MoB2 - x grains surrounded by an amorphous tissue phase (a-B for binary, and a-BCx for ternary films). With increasing carbon content grain sizes was found to decrease (from 16 to 5 nm), and above 23 at.% carbon the films deposited at room temperature were X-ray amorphous. Scanning transmission electron microscopy and energy dispersive X-ray spectroscopy reveal that these films contain Mo-rich and Mo-poor regions, and thus are two-phase amorphous nanocomposites. Low-carbon content samples exhibited a friction coefficient against the steel counter surface of 1.1; this was reduced to 0.8 for high carbon-content films. Analysis of the tribofilm revealed formation of molybdenum oxide and amorphous carbon, however without significant lubricating effect at room temperature. Hardness and elastic modulus decrease with carbon content from similar to 29 to similar to 22 GPa and similar to 526 to similar to 326 GPa. These values give an WE ratio of 0.06 to 0.07, indicating brittle material. Resistivity was found to increase with carbon content from similar to 175 mu Omega cm for binary Mo-B to similar to 395 mu Omega cm for Mo-B-C thin film with 37 at.% of C. Therefore all the above results suggest that the Mo-B-C films are not suitable for sliding electrical contacts. (C) 2016 Elsevier B.V. All rights reserved.