Implementation of diffractive optical element in four-wave mixing scheme for ex situ characterization of hydride vapor phase epitaxy-grown GaN layers

A holographic beam splitter has been integrated into a picosecond four-wave mixing (FWM) scheme. This modification significantly simplified the procedure of dynamic grating recording, thus making the FWM technique an easy-to-use tool for the holographic characterization of wide band gap materials. The novel FWM scheme was applied for characterization of hydride vapor phase epitaxy-grown undoped GaN layers of different thickness. It allowed the determination of carrier lifetime, diffusion coefficient, and carrier diffusion length by optical means, as well as the study of carrier recombination peculiarities with respect to dislocation and excess carrier density.     

The effect of initial conditions on ignition and burnup of the anthracite culm dust during its combustion together with natural gas

The effects on ignition length of fractional composition of coal dust, hot air temperature, primary air excess coefficient, degree of mixing of primary and secondary air, and heat fraction of gas in a mixture of fuels are investigated.     

Selecting a retrofitting profile for the TGME-444 boiler at the Rostov TETs-2 cogeneration station

Hydraulic misalignments in the steam superheating surfaces and possible changes in the thermal circuit of a TGME-444 boiler are analyzed, and the retrofitting version of this boiler that was drawn up from the results of this analysis and implemented at the Rostov TETs-2 cogeneration station in 2007 is presented. The improvement in the operational reliability of the retrofitted boiler is demonstrated.     

Electrochemical etching of <Emphasis Type="Italic">p–n</Emphasis>-GaN/AlGaN photoelectrodes

Specific features of etching of GaN/AlGaN p–n structures in a KOH-based electrolyte have been studied. It was found that the corrosion process first passes across p layers through vertical channels associated with threading structural defects. Then, the corrosion process occurs in the lateral direction along n layers of the structure, with local hollows and voids thereby formed. The lateral etching is due to the presence of positive piezoelectric charges at boundaries of n-AlGaN and n-GaN layers and positively charged ionized donors in the space-charge region of the p–n junction.     

Low-temperature time-resolved photoluminescence in InGaN/GaN quantum wells

The results of the investigation of low-temperature time-resolved photoluminescence in undoped and Si-doped In_0.2Ga_0.8N/GaN structures, which contain 12 quantum wells of width 60 Å separated by barriers of width 60 Å, are reported. The structures were grown by the MOCVD technique on sapphire substrates. The photoluminescence properties observed are explained by the manifestation of two-dimensional donor-acceptor recombination. These properties are the high-energy shift of the peak upon increasing the pumping intensity, a low-energy shift with increasing delay time, and a power law of luminescence decay of the t ^-γ type. The estimates of the total binding energy for donor and acceptor centers are given. This energy is 340 and 250 meV for Si-doped and undoped quantum wells, respectively. The role of the mosaic structure, which is typical for Group III hexagonal nitrides, is discussed as a factor favorable for the formation of donor-acceptor pairs.     

Studying the Sensitivity of Graphene for Biosensor Applications

Technical Physics Letters - We have studied the response of graphene-film-based chips on SiC substrates (the relative change in the chip resistance) to coming into contact with fluorescein...     

Geoecological Assessment of the Malyi Khingan Ridge Area Using Land Surface Remote Sensing Data

The spotlight is on the use of Earth remote sensing data in geoecological assessment of the Malyi Khingan Ridge area in the Far East. Based on the analysis of satellite observations over the Sutara gold placer mining range, the time variation of the disturbed land is determined. It is found that natural recovery of bio-geo-cenosis takes an active part in the process. Using the normalized difference vegetation index (NDVI), the behavior and rates of self-healing of the disturbed lands are assessed. Complete recovery of vegetation in gold placer mining areas up to a level comparable with the adjacent territories takes 7 to 10 years.

     

Diversity of Properties of Device Structures Based on Group-III Nitrides,Related to Modification of the Fractal-Percolation System

A fractal-percolation system that includes extended defects and random fluctuations in the alloy composition is formed during the growth of device structures based on Group-III nitrides. It is established that the specific features of this system are determined not only by the growth conditions. It is shown that the diversity of the electrical and optical properties of InGaN/GaN LEDs (light-emitting diodes) emitting at wavelengths of 450–460 and 519–530 nm, as well as that of the electrical properties of AlGaN/GaN HEMT (high-electron-mobility transistor) structures, is due to modification of the properties of the fractal-percolation system both during the growth process and under the action of the injection current and irradiation. The influence exerted by these specific features on the service life of light-emitting devices and on the reliability of AlGaN/GaN HEMT structures is discussed.

     

Method for Concurrent Identification of a Linear Dynamic Measurement System Based on Preliminary Nonlinear Transformation of the Input Signal

Measurement Techniques - We consider the problem of the concurrent identification of a linear dynamic measuring system with an unknown input signal under the influence of various destabilizing...