Optical properties of germanium monolayers on silicon

Photoluminescence and Raman spectra of thin germanium layers grown on silicon at a low temperature (250°C) have been studied. In structures of this kind, in contrast to those grown at high temperatures, luminescence from quantum wells is observed at germanium layer thicknesses exceeding ～9 monolayers (ML). With the development of misfit dislocations, the luminescence lines of quantum wells are shifted to higher energies and transverse optical (TO) phonons involved in the luminescence are confined to a quasi-2D germanium layer. Introduction of an additional relaxed Si_0.95Ge_0.05 layer into the multilayer Ge/Si structure leads to a substantial rise in the intensity and narrowing of the luminescence line associated with quantum dots (to 24 meV), which points to their significant ordering.     

Photoluminescence from germanium quantum wells and quantum dots in silicon grown by MBE at low temperature

Semiconductors - The low-temperature (T=2 K) photoluminescence (PL) has been studied in Si/Ge structures grown by MBE at a low (250–350°C) temperature of Ge deposition. The luminescence...     

Room temperature λ=1.3 µm photoluminescence from InGaAs quantum dots on (001) Si substrate

GaAs/In_xGa_1−x As quantum dot heterostructures exhibiting high-intensity λ=1.3 μm photoluminescence at room temperature have been grown on (001) Si substrate with a Si_1−x Ge_x buffer layer. The growth was done successively on two MBE machines with sample transfer via the atmosphere. The results obtained by the study of the structure growth process by means of high-energy electron diffraction are presented. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 36, No. 5, 2002, pp. 565–568. Original Russian Text Copyright ? 2002 by Burbaev, Kazakov, Kurbatov, Rzaev, Tsvetkov, Tsekhosh.     

An avalanche photodiode with metal-insulator-semiconductor properties

A new design of the avalanche photodetector combining the avalanche photodiode and MIS structure properties was tested. The noise and high-frequency properties of the device were studied. The device exhibited a noise factor of less than 10 at a high multiplication factor (M>1000) even with hole injection. This is indicative of a drastic change in the effective ratio of the coefficients of impact ionization by electrons and holes in favor of the latter. Measurements of the photosensitivity distribution over a photodetector area for M=8000 showed a high uniformity.     

Use of magnetic field screening by high-temperature superconducting films to switch microwave signals

The efficiency with which YBCO films screen an alternating magnetic field near the superconducting transition was measured. In the decimeter range measurements were made of the characteristics of a switch whose operating principle was based on the change in the screening of an alternating magnetic field by a superconducting transition. Pis’ma Zh. Tekh. Fiz. 24, 76–81 (July 12, 1998)     

Lateral conductivity of <Emphasis Type="Italic">p</Emphasis>-type doped Si/Ge island structures

Numerical calculations of the conductance in structures with doping modulated along the current-flow direction are carried out taking into account band offsets at the interfaces between high-and low-resistivity regions. It is found that such structures exhibit S-shaped current-voltage characteristics; in the limiting case, there should be a negative-conductance region, with the abruptness of the heterojunction between the narrow-and wide-gap sections of the structure and the doping level being the critically important parameters in the theory. p-type Si/Si_1?x Ge _x island structures with different sizes of islands and different band offsets were grown by molecular-beam epitaxy. Theoretical results are compared with the data on lateral conductance of the grown structures.     

High-frequency properties of avalanche multiplication of photocarriers in structures with negative feedback

The high-frequency characteristics of photosensitive avalanche Si-SiC structures were studied. It is shown that their high-speed operation is substantially superior to that of silicon avalanche photodiodes. A theoretical analysis of the high-frequency properties of avalanche photodiodes is carried out and analytical expressions for the gain-bandwidth product are obtained. It is shown that this product is not a universal parameter for a metal-insulator-semiconductor structure with a negative feedback, since, for high amplification factors, the effective value of the relation of the impact-ionization coefficients for different types of charge carriers in such structures turns out to be significantly different from that in avalanche photodiodes.