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The results of studying the photoelectric characteristics of an nBn structure are presented. The photodiodes based on such structures may have a cutoff wavelength as high as 5 μm. Calculations based on these results show that such photodiodes have a threshold photosensitivity comparable with that of traditional analogs. An energy band diagram of the nBn structure is proposed based on experimental results and theoretical estimations; this diagram makes it possible to estimate the effect of potential barriers in the valence band of the wide-gap layer and at its boundaries with narrow-gap layers on the nBn-based photodiode sensitivity. The experimental results of studying the dependence of the photocurrent thermal-activation energy on the photodiode bias turned out to be important for developing the model.

GaAs light-emitting (LED) and HEMT structures with δ-doped regions, InGaAs/GaAs quantum wells, and surface layers of InAs/GaAs quantum dots were studied by means of the electrochemical capacitance- voltage profiling technique. The concentration depth profiles of free charge carriers were obtained. Charges accumulated in quantum wells and quantum dots, as well as the doping levels of the emitter and δ layers were determined. The band structure and free carrier density distribution over the depth of the samples with different quantum well geometry were simulated. The specific features of electrochemical capacitance- voltage profiling in different heterostructure types are analyzed. A method of integration of capacitance- voltage curves at each etching stage was suggested. This method provides the efficient separation of responses from closely located layers, particularly the quantum well and δ layer.

AbstractWe performed numerical self-consistent solution of Schrödinger and Poisson equations for GaAs/InGaAs/AlGaAs pHEMT structures with quantum well. Based on the results we calculated optical transition matrix elements and photoluminescence spectra of such structures with the same design and different parameters (such as doping level and epitaxial layers width). In the photoluminescence spectra calculations three fitting parameters have been used. These parameters are GaAs/InGaAs valence band offset in strained quantum well, hole quasi Fermi level and inhomogeneous broadening. The PL peaks amplitudes and positions dependencies on the structure parameters were established. These dependencies can be used as the basis for pHEMT structure non-destructive diagnostics.

Photoelectric properties of different stressed InGaAs/AlGaAs heterostructures with quantum wells grown by the method of molecular beam epitaxy on GaAs substrates for mid-wavelength infrared largeformat photodetector arrays operating in the spectral range 3–5 μm have been investigated. It has been shown that the change in the composition of barrier layers leads to a significant shift of the photosensitivity spectra of such heterostructures.

Structural characterization of the epitaxial thin aluminum nitride (AlN) 1-μm-thick films grown on SiC/(111)Si substrate by molecular beam epitaxy method was done. The films are shown to be single crystals of (0002) orientation with parameter full width half maximum FWHMωθ = 0.5°. A comparative study of the film electrical properties with the films grown by chloride vapor-phase epitaxy has revealed the difference in polar axis orientation, pyroelectric response, and piezoelectric hystograms.

An optical pyrometer designed for precision measurement of the GaAs substrate temperature during MBE growth is considered. The pyrometer can be calibrated against a certain characteristic absolute temperature that is visually determined from a change in the RHEED pattern. This enables one to calculate the absolute temperature of the substrate with regard to its radiant emissivity and minimize the inaccuracy of radiation temperature measurement. The inaccuracy is associated with the deposition of growth products on the pyrometer window.

The parameters of high-power laser diodes operating at λ=0.94 μm, based on MBE-grown In0.1Ga0.9As/AlGaAs/GaAs quantum-dimensional heterostructures, are reported. The laser diodes manufactured using an optimized MBE technology and specially selected dopant profiles are characterized by a lowthreshold current density, a high optical output power, a high differential quantum efficiency, and a long working life (above 10000 h).

The growth rate evolution versus V/III ratio and substrate temperature was studied by means of optical reflectivity during MBE of GaN layers using NH3 as nitrogen source. The GaN desorption becomes observable at temperatures above 800°C and causes the reduction of growth rate accompanied with the surface roughening at temperatures above 850-870°C. Unlike GaAs, which evaporates in accordance with the action mass law, the desorption rate of GaN is found to be almost independent of V/III ratio within the N-rich growth conditions. The activation energy for GaN desorption during the growth is found to be (3.2±0.1)eV. This value is very close to the activation energy for free evaporation. At V/III ratio values exceeding 200 the GaN growth rate reduction caused by violation of the molecular flow regime is observed. The Mg-doped samples grown under these extreme conditions tend to have improved acceptor activation and thus p-type conductivity.

CAT was carried out in 110 patients with gastric carcinoma and its findings compared with the intraoperative findings. CAT involved a polypositional scanning (depending on the tumor site) against the background of oral contrast label of the stomach and intestine. CAT potentialities in the diagnosis of gastric carcinoma, assessment of the tumor size and involvement of the adjacent organs and structures, detection of the metastases were studied. Use of CAT in complex with other methods will help choose the optimal treatment strategy and determine the volume of supposed surgical intervention.