Fabrication of Strain-Relaxed Si<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript>x</Subscript>/Si(001) Buffer Layers of Low Surface Roughness

The results are presented of the fabrication of strain-relaxed graded Si_{1 − x} Ge_x/Si(001) buffer layers with a maximum Ge fraction of about 0.25 that have a low density of threading dislocations (<10⁶ cm⁻²) and low surface roughness. The buffer layers are grown by atmospheric-pressure hydride CVD. It is found that chemical mechanical polishing can reduce their surface roughness to a level comparable with that of the original Si(001) substrates. It is shown that the polished buffer layers can serve as substrates for MBE-grown SiGe/Si heterostructures.__________Translated from Mikroelektronika, Vol. 34, No. 4, 2005, pp. 243–250.Original Russian Text Copyright © 2005 by Vostokov, Drozdov, Krasil’nik, Kuznetsov, Novikov, Perevoshchikov, Shaleev.     

Stability of a full nonlinear electromagnetic suspension under decentralized control

Stability of the zero equilibrium state of a full electromagnetic suspension of a rotor under decentralized control of each bearing is proved. The obtained results may be used for selecting the structure of the system for control of electromagnetic bearings.     

Electrical and structural parameters of YBCO films obtained by repeated growth cycles

We have studied changes in the electrical and structural characteristics of YBa₂Cu₃O_{7 − δ} (YBCO) films in the course of step-by-step increase in their thicknesses up to about 1 μm in a series of repeated magnetron sputtering growth cycles. It is established that high quality of the films is not deteriorated by interrupts in the growth process, which involve the formation of patterns on the sample and measurement of its electrical properties in liquid nitrogen. These results show the possibility of introducing intermediate stages of lithography into the process of YBCO deposition for the formation of structures with nonuniform thicknesses.     

MOVPE of structures with aluminum nanocluster layers in a GaAs matrix

Metalorganic vapor phase epitaxy (MOVPE) was used to grow semiconductor structures comprising a GaAs single crystal matrix with incorporated layers of aluminum nanoclusters (Al-NCs). A new regime of GaAs overgrowth on Al-NC layers is proposed, which ensures planarization of the semiconductor layer surface at a thickness comparable with the height of Al-NCs.     

Admittance and nonlinear capacitance of a multilayer metal-semiconductor structure

Nonlinear properties of capacitance and frequency dependence of admittance for a multilayer metal-semiconductor structure are studied theoretically. It is shown that admittance of such structure depends on the frequency of a small probe signal. The voltage dependence of capacitance measured using a low-frequency probe signal can be nonmonotonic. The behavior of the structure’s capacitance at a large amplitude of external signal is studied. After some time from the instant of switching-on of the high-frequency signal, the system is found in a steady state with certain charge of the metal layer and predefined capacitance of the system. In the steady state, the charge of metal and the capacitance do not depend on the instantaneous value of the voltage; rather, they are governed by the signal’s amplitude.     

Microstructure and properties of aluminum contacts formed on GaAs(100) by low pressure chemical vapor deposition with dimethylethylamine alane source

We report on a low pressure chemical vapor deposition of metallic thin aluminum films on GaAs (001) with a dimethylethylamine alane (DMEAA) source and H₂ as a carrier gas. The deposition temperatures varied in the range 130–360°C. Integrated volumes for Al (111), (100), (110)R, and (110) grains were estimated by the x-ray diffraction technique and the growth temperature values preferred for every type of grains were observed. The experimentally observed dominance of Al(110)R over Al(110), irrespective of the substrate miscut direction, supports the GaAs(100) inner anisotropy effect on the Al grain orientation. Electrical resistivity was 5 ·cm for the best Al films. The Schottky barrier heights were near a 0.7 eV level and the ideality factor n=1.1. Nonalloyed ohmic contacts were fabricated on an n-type GaAs epitaxial layer with an additional set of Si-layers near the Al/GaAs interface. Specific contact resistance, c=7 cm², was measured. Best contacts were obtained at a deposition temperature lower than 250°C.     

High-sensitivity accelerometer based on cold emission principle

A possibility for fabrication of a high-sensitivity accelerometer is considered. The linear acceleration of a sensor causes displacement of the proof mass electrode. The displacement detector is based on a strong dependence of the tunneling or cold emission current on the gap between the electrodes. The geometry of the electrodes that provides the best sensitivity is determined. The accelerometer with tunneling-emission electrodes is fabricated. At frequencies up to 5 kHz the resolution reaches 10/sup -4/ g/Hz/sup 1/2/ in the tunneling mode and 10/sup -3/ g/Hz/sup 1/2/ in the emission mode.     

Modification of Ag containing photo-thermo-refractive glasses induced by electron-beam irradiation

We present the experimental investigation of formation and growth of Ag nanocrystals in silica photo-thermo-refractive glasses under the electron-beam irradiation and subsequent thermal treatment. The influence of electron irradiation fluence, current density and thermal treatment conditions on nanocrystal growth dynamic has been investigated. Theoretical models and computer simulation of main processes which take place during electron-beam irradiation are presented.     

Effect of the parameters of sapphire substrates on the crystalline quality of GaN layers

The effect of certain types of sapphire substrate treatment on the properties of gallium nitride layers grown by metal-organic vapor-phase epitaxy is investigated.