Time-resolved photoluminescence of polycrystalline GaN layers on metal substrates

The low-temperature time-resolved photoluminescence of polycrystalline GaN layers grown by molecular beam epitaxy on metal substrates (Mo and Ta) was investigated. The photoluminescence spectra observed include two emission bands in the ultraviolet spectral region. We assign one of these bands to recombination processes inside cubic nanocrystallites, which are formed in the hexagonal polycrystalline GaN host. The recombination radiation of cubic nanocrystallites is enhanced due to predominant trapping of the nonequilibrium electron-hole pairs in these crystallites.     

Model of the Radio Images of Objects in Holographic In-Plane Surveillance Radar Systems Based on an Analytical Approximation Method

A simple analytical approximation for computing radio images of 3D objects is proposed for an airborne MIMO-type holographic in-plane surveillance radar systems (PSRSs). The model is intended for realtime estimation of the quality of 3D images in such PSRSs during selection of the main parameters of the MIMO antenna system, the frequency band, and the bandwidth of the sounding signal. The results can also be applied to conventional PSRSs, a factor that makes it possible to perform a comparative analysis of PSRS versions and select the PSRS embodiment.     

Phase-synchroniser based on gm-C all-pass filter chain with sliding mode control

Phase-synchronisers have many applications in VLSI circuit designs. They are used in CMOS RF circuits including phase (de)modulators, phase recovery circuits, multiphase synthesis, etc. In this article, a phase-synchroniser based on g_m-C all-pass filter chain with sliding mode control is presented. The filter chain provides good controllable delay characteristics over the full range of phase and frequency regulation, without deterioration of input signal amplitude and waveform, while the sliding mode control enables us to achieve fast and predetermined finite locking time. IHP 0.25 µm SiGe BiCMOS technology has been used in design and verification processes. The circuit operates in the frequency range from 33 MHz up to 150 MHz. Simulation results indicate that it is possible to achieve very fast synchronisation time period, which is approximately four time intervals of the input signal during normal operation, and 20 time intervals during power-on.     

Nonstoichiometry and solubility of impurity in In-doped PbTe films on Si substrates

The chemical quantitative composition, phase constitution, and crystal structure of doped with In lead telluride films on Si (1 0 0) or SiO₂/Si (1 0 0) substrates have been studied in this work. By EPMA and atomic absorption measurements, it has been found that the concentration of In atoms y_In varied from 0.0011 to 0.045 in these deposited Pb_1−yIn_yTe films. The results of EPMA, SEM, and X-ray diffraction (XRD) measurements show that formation of In solid solutions in lead telluride matrix revealed not only in PbTe–InTe cross-section, but in PbTe–In₂Te₃ pseudobinary system also. The results of XRD show that the lattice parameter a_PbTe of PbTeIn/Si and PbTeIn/SiO₂/Si heterostructures is described by nonmonotone function and does not obey the Vegard's law within concentration interval 0.0011y_In0.045.     

A 1280 × 1024 CMOS visible-range photodetector chip with a pixel size of 13 × 13 μm

A photodetector array chip for detection of the optical signal in a wave range of 0.4–1.0 μm; conversion of the optical signal into the electric signal; and its extraction in the analog form to 1, 2, 4, 8, or 16 outputs has been designed, fabricated, and studied. The main parameters of this chip are the following: the charge capacity is up to 200000 electrons, the frame rate is higher than 600 Hz at the maximum resolution, and the integrated sensitivity is up to 1000 V/(lx s).     

Wannier-Stark states in a superlattice of InAs/GaAs quantum dots

Electron and hole emission from states of a ten-layer system of tunneling-coupled vertically correlated InAs/GaAs quantum dots (QDs) is studied experimentally by capacitance—voltage measurements and deep-level transient spectroscopy. The thickness of GaAs interlayers separating sheets of InAs QDs was ≈3 nm, as determined from transmission electron microscope images. It is found that the periodic multimo-dal DLTS spectrum of this structure exhibits a pronounced linear shift as the reverse-bias voltage U _r applied to the structure is varied. The observed behavior is a manifestation of the Wannier—Stark effect in the InAs/GaAs superlattice, where the presence of an external electric field leads to the suppression of coupling between the wave functions of electron states forming the miniband and to the appearance of a series of discrete levels called Wannier—Stark ladder states.     

Mechanisms of InGaAlAs solid solution decomposition stimulated by InAs quantum dots

Mechanisms of InGaAlAs solid solution decomposition stimulated by a purposely deposited layer of InAs quantum dots are studied. Decomposition of the solid solution results in an increase in the effective quantum dot size and the shift of the photoluminescence line to as far as 1.3 μm. When aluminum atoms are added to the solid solution, the effect of In atom “conservation” within the dots is observed, which also causes an increase in the effective dot size. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 34, No. 3, 2000, pp. 330–333. Original Russian Text Copyright ? 2000 by Tsatsul’nikov, Volovik, Bedarev, Zhukov, Kovsh, Ledentsov, Maksimov, Maleev, Musikhin, Ustinov, Bert, Kop’ev, Bimberg, Alferov.     

Piezoelectric effect in GaAs nanowires

The anomalous piezoelectric effect in GaAs nanowires was detected (the piezoelectric module d ₃₃ ≈ 26 pC/N). This result can be explained by the dominant content of the phase with the wurtzite-type crystal structure in GaAs nanowires and an increased pressing force on the contact layer.     

Effect of electron-electron and electron-hole collisions on intraband population inversion of electrons in stepped quantum wells

The effect of intersubband electron-electron (e-e) and electron-hole (e-h) scattering on intraband population inversion of electrons in a stepped InGaAs/AlGaAs quantum well is investigated. The characteristic times of the most probable e-e and e-h processes, which affect the electron densities on the excited levels, are calculated for the temperature range 80–300 K. Dependences of these times on the electron and hole density on the ground levels are studied. Temperature dependences of the intraband inversion of population for two nonequilibrium densities are calculated by solving a system of rate equations. It is shown that the intersubband e-e and e-h scattering only slightly affects the population inversion for electron densities below 1×10¹² cm^?2.