Properties of arsenic-implanted Hg1-xCdxTe MBE films

Defect structure of arsenic-implanted Hg1-xCdxTe films (x=0.23–0.30) grown with molecular-beam epitaxy on Si substrates was investigated with the use of optical methods and by studying the electrical properties of the films. The structural perfection of the films remained higher after implantation with more energetic arsenic ions (350 keV vs 190 keV). 100%-activation of implanted ions as a result of post-implantation annealing was achieved, as well as the effective removal of radiation-induced donor defects. In some samples, however, activation of acceptor-like defects not related to mercury vacancies as a result of annealing was observed, possibly related to the effect of the substrate

Accumulation and annealing of radiation donor defects in arsenic-implanted Hg0.7Cd0.3Te films

Processes of accumulation and annealing of radiation-induced donor defects in arsenic-implanted Hg0.7Cd0.3Te films were studied with the use of the Hall-effect measurements with processing the data with mobility spectrum analysis. A substantial difference in the effects of arsenic implantation and post-implantation activation annealing on the properties of implanted layers and photodiode ‘base’ layers in Hg0.7Cd0.3Te and Hg0.8Cd0.2Te films was established and tentatively explained

Localization and nature of radiation donor defects in the arsenic implanted CdHgTe films grown by MBE

By profiling the electrical parameters of the arsenic implanted CdHgTe films, grown by molecular bea

SYNTHESIS OF THICK GALLIUM NITRIDE LAYERS BY METHOD OF MULTI-STAGE GROWTH ON SUBSTRATES WITH COLUMN STRUCTURE

Subject of Research.The paper deals with processes of formation and transformation of defects during multi-stage growth of thick gallium nitride layers with hydride vapor phase epitaxy on GaN/Al2O3 substrates with buried column pattern formed with the use of metal-organic vapor phase epitaxy. Methods. The growth of initial GaN layers was performed with the use of metal-organic vapor phase epitaxy. On the surface of the initial layers columns with the height of 800 nm were generated by means of ion etching. These columns were overgrown with 3-4 µm-thick GaN layers. On thus formed substrate multi-stage growth of GaN layers was performed with the use of hydride vapor-phase epitaxy. The total thickness of GaN layers was 100-1500 µm. The grown layers were studied by optical and electron microscopy and Raman spectroscopy. Main Results. Density of threading dislocations in the layers grown by hydride vapor-phase epitaxy was (3-6)·107 cm-2, that was one order of magnitude lower than in the used substrate, and two to three orders lower than dislocation density in typical GaN layers grown on commercial sapphire substrates. Raman spectroscopy data were indicative of low level of mechanical stress in the layers and their high structural uniformity. It was established that under multi-stage growth conditions, non-catastrophic cracks (those that do not cause sample destruction) are able to transform into macropores and appear to be an important structural element, serving to stress relaxation in the bulk of thick gallium nitride layers grown on foreign substrates. Practical Relevance. The results of the study can be used in the development of III-nitride heterostructures for optoelectronics and high-power and high-frequency microelectronics

Fluence dependence of nanosize defect layers in arsenic implanted HgCdTe epitaxial films studied with TEM/HRTEM

We report on the results of comparative study of fluence dependence of defect layers in molecular-beam epitaxy-grown epitaxial film of p-Hg1-х CdхTe (х=0.22) implanted with arsenic ions with 190 keV energy and fluence 1012, 1013, and 1014 cm-2

Discrete mobility-spectrum analysis and its application to transport studies in HgCdTe

A detailed consideration of the discrete mobility-spectrum analysis (DMSA) method and its application to transport studies in HgCdTe is given. First, a brief review of the methods of the analysis of field dependences of the Hall coefficient and conductivity in HgCdTe-based structures with a multi-carrier mobility spectrum is presented. The advantages and drawbacks of these methods, which include original mobility-spectrum analysis by Beck and Anderson, multi-carrier fitting and iterative approach by Dziuba and Górska, and the later developments of these techniques, are considered. The properties of the envelope of the mobility spectrum are analyzed, and the specifics of DMSA are presented. Analysis of some magnetic-field B dependences of conductivity tensor components σxx(B) and σxy(B) presented in the literature is performed with DMSA, and the results are compared to those obtained with other methods

Determination of the parameters of multi-carrier spectrum in CdHgTe. II. Discrete mobility spectrum analysis

The paper, which consists of two parts, considers in detail the method of discrete mobility spectrum analysis (DMSA) proposed by the authors as well as its application to determine the parameters of charge carriers in CdHgTe. The first part of the work was a brief review of the existing methods for analyzing the field dependences of the Hall coefficient and conductivity in structures with a multi-carrier spectrum of charge carriers. In the second part of the work, the physical properties of the mobility spectrum envelope in the mobility spectrum analysis (MSA) method are analyzed and the main idea, features, and algorithm of the DMSA method are presented. On the example of studying the electrical properties of numerous samples of CdHgTe epitaxial films, the high sensitivity of the DMSA was confirmed. Using DMSA, we analyzed a number of dependences of the conductivity tensor components σxx and σxy on the magnetic field B, available in the literature, and compared the results of the analysis with those obtained with other methods

Analysis of Erbium and Vanadium Diffusion in Porous Silicon Carbide

Experimental data on diffusion of erbium and vanadium in porous and nonporous silicon carbide at 1700 and 2200°C have been used for modelling diffusion in porous SiC. It is shown that the consideration of pore structure modification under annealing via vacancy redistribution allows for satisfactory description of dopant diffusion. As expected, important contribution to the diffusion in the porous medium is found to be made by the walls of the pores: in SiC, the vacancy surface diffusion coefficient on the walls appears to exceed that in the bulk of the material by an order of magnitude. When thermal treatment transforms pore channels into closed voids, pathways for accelerated diffusion cease to exist and diffusion rates in porous and nonporous SiC become similar

Determination of the parameters of multi-carrier spectrum in CdHgTe. I. A review of mobility spectrum analysis methods

The paper consisting of two parts presents a detailed consideration of the proposed method of discrete mobility spectrum analysis and its application for studying the parameters of charge carriers in CdHgTe. The first part of the paper is a brief review of the existing methods of the analysis of the magnetic-field dependences of the Hall coefficient and conductivity in structures with a multi-carrier spectrum. The underlying principles of various methods are considered, including the original mobility spectrum analysis proposed by Beck and Anderson, the multi-carrier fitting, and the iterative method developed by Dziuba and Górska, as well as more recent developments. The advantages, drawbacks, and limits of applicability of these methods are iscussed

FREQUENCY CHARACTERISTICS OF MODERN LED PHOSPHOR MATERIALS

Frequency characteristics of modern LED phosphor materials have been considered for the purpose of assessing the prospects of phosphor-based LEDs in wireless communication data systems which use optical wavelengths. The measurements have been carried out on the dependence of the emission intensity of single LEDs and LED chip-on-board modules with phosphors based on yttrium-aluminum and lutetium-aluminum garnets (with or without addition of nitridebased phosphors) as well as silicate-based phosphors, on the frequency of electric pulses exciting the emission. It was shown that from the point of view of data transmission rate, garnet-based phosphors (including systems with added nitride phosphors) are more promising than silicate–based ones. Garnet-based materials can be used in optical communication data systems with bandwidth (without extra modulation applied) up to 3 MHz with single–chip LEDs and up to 4.5 MHz with 9- chip LED chip-on-board modules. The results of the work indicate that a significant part of white LEDs used in general lighting systems can be even now used for data transfer, for example, in systems assisting positioning in closed spaces to facilitate people searching necessary rooms or object