Scattering of hot electrons by neutral acceptors in GaAs/AlAs quantum well structures

The optical alignment of hot electrons and its destruction in a magnetic field under conditions when electron scattering by neutral acceptors plays a large role is investigated. This makes it possible to determine the probability of the scattering of hot electrons from an initial photoexcited state, as well as the times characterizing the energy and momentum relaxation of hot electrons on scattering by neutral acceptors. The experimental results are compared with calculations. Fiz. Tekh. Poluprovodn. 32, 866–875 (July 1998)     

Mechanisms of excitation of the f-f emission in silicon codoped with erbium and oxygen

The Er₂O₃ cluster in silicon is discussed as a possible source of the Er-related emission in Si:Er, O. We propose a mechanism that gives a simple explanation of the high efficiency of Er atom excitation in Er-O clusters. The cases of photoluminescence and electroluminescence are considered. In the case of photoluminescence the high efficiency of Er excitation is attributed to the electron state localized at the Er-O cluster. The excitation of f-shell electrons in Er atoms occurs via the Auger recombination of the exciton bound at the Er-O cluster. We calculate the rate of this Auger process and discuss the dependence of the photoluminescence intensity on the carrier concentration. In the case of electroluminescence under reverse bias the impact excitation cross section is enhanced due to resonant scattering of the hot electrons at the quasi-discrete levels formed by the Er-O cluster quantum-well potential. The calculated impact excitation cross section is close to the experimental value. Fiz. Tekh. Poluprovodn. 33, 664–670 (June 1999) Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

The role of macrodefects in electronic and ionic processes in wide-band II–VI semiconductors

This paper discusses the electrical, photoelectric, and photoluminescence characteristics and the ESR spectra of CdS crystals with various dislocation densities (γ=10²–10⁵ cm⁻²). It is found that the presence of mobile donors and of dislocations with density γ>10³–10⁴ cm⁻² has a number of specific effects: anisotropy of the electric-field-induced conductivity, athermal diffusion of donors under the action of ultrasound, distortion of the shape of the edge-luminescence spectrum, and photostimulated degradation of the photosensitivity and photoluminescence. The dependence of the type of macrodefects and the optical strength of the crystals on the fabrication process is studied. Fiz. Tekh. Poluprovodn. 32, 641–645 (June 1998)     

Effect of γ irradiation on the photoluminescence kinetics of porous silicon

The effect of γ irradiation on the photoluminescence decay dynamics in porous silicon is investigated. Growth of the photoluminescence intensity and decrease of the decay time in irradiated porous silicon are explained by a lowering of the barriers to recombination of spatially separated electrons and holes via tunneling. The γ irradiation of porous silicon leads to a greater dispersion of the decay time. Fiz. Tekh. Poluprovodn. 33, 1462–1464 (December 1999)     

The problem of intermediate temperatures or electric fields in the scattering of hot electrons by acoustic phonons

An approximate expression is derived for the momentum relaxation time in the quasielastic scattering of hot electrons by acoustic phonons as a function of the electron energy and the lattice temperature. The mobility and the dependence of the impurity breakdown electric field on the degree of compensation are calculated in the electron-temperature approximation. The results of the calculations are in good agreement with the experimental for n-type Ge. Fiz. Tekh. Poluprovodn. 31, 1071–1073 (September 1997)     

Trapping of hot electrons at repulsive centers under transverse runaway conditions

The trapping of hot electrons at repulsive centers under transverse runaway conditions is calculated. The dependence of the trapping probability on the Sommerfeld factor and the exponential dependence of the trapping probability on the energy of the tunneled electron are taken into account. It is shown that the latter dependence plays an important role near the threshold of transverse runaway of hot electrons, while far from the threshold the Bonch-Bruevich trapping probability is a good approximation. Fiz. Tekh. Poluprovodn. 31, 268–270 (February 1997)     

Reciprocal drag of electrons and phonons in strongly doped HgFeSe semiconductors

The previously observed unusual dependences of the thermoelectric and thermomagnetic coefficients of strongly doped HgFeSe crystals on temperature and magnetic field intensity are studied theoretically. It is shown that the observed dependences are due to the combined effect of electron scattering by spatially correlated charged donors Fe(3+) at low temperatures and the reciprocal drag of electrons and phonons, which plays a large role in semiconductors with a high density of itinerant charge carriers. Fiz. Tekh. Poluprovodn. 33, 701–707 (June 1999)     

Negative dynamic differential conductivity at the cyclotron frequency in Ga1−x AlxAs under conditions of ballistic intervalley electron transfer

It is theoretically shown that under certain conditions a cyclotron resonance maser can be fabricated based on n-Ga_1−x Al_xAs-type materials. Low temperatures and strong crossed fields (E⊥H) are considered. In these fields the electrons in the lower (light) valley of the conduction band dynamically (ballistically) transit the band up to the onset energy of intervalley scattering ɛ ₀. Studies were carried out on solid solutions with composition 0<x<0.39 (ɛ ₀=(2–17)ℏω*, where ℏω* is the intervalley phonon energy). The magnitudes of the E and H fields were varied within the limits E=5–20 kV/cm and H=6–40 kOe. This produced a smooth change in the transit conditions in the passive region (ɛ<ɛ ₀), which makes it possible to obtain the desired frequency dependence of the differential conductivity (DC), σ(ω). As our studies show, previously unknown, interesting peculiarities of the hot electron system appear under these conditions. Fiz. Tekh. Poluprovodn. 32, 164–170 (February 1998)     

Transport and optical properties of tin δ-doped GaAs structures

The transport and optical properties of tin δ layers in GaAs are investigated as functions of the Sn concentration. The Shubnikov-de Haas and Hall effects are measured in the temperature range 0.4–12 K in magnetic fields up to 38 T. The band diagrams and quantum mobilities of electrons in the quantum-well subbands are calculated. Features associated with electronic transitions from quantum-well levels are found in the photoluminescence spectra of the structures. Oscillations of the resistance are observed in a magnetic field parallel to the δ layer and are attributed to features in the density of states at the Fermi level. Fiz. Tekh. Poluprovodn. 33, 839–846 (July 1999)     

Photoluminescence of Si3N4 films implanted with Ge+ and Ar+ ions

The room-temperature photoluminescence emission and excitation spectra of Si₃N₄ films implanted with Ge⁺ and Ar⁺ ions were investigated as a function of the ion dose and temperature of subsequent annealing. It was established that the implantation of bond-forming Ge atoms during annealing right up to temperature T _a=1000 °C stimulates the formation of centers emitting in the green and violet regions of the spectrum. Implantation of inert Ar⁺ ions introduces predominantly nonradiative defect centers. Comparative analysis of the photoluminescence spectra, Rutherford backscattering data, and Raman scattering spectra shows that the radiative recombination is due not to quantum-well effects in Ge nanocrystals but rather recombination at the defects ≡Si-Si≡, ≡Si-Ge≡, and ≡Ge-Ge≡. Fiz. Tekh. Poluprovodn. 33, 559–566 (May 1999)     

Enhanced formation of thermal donors in irradiated germanium: Local vibrational mode spectroscopy

Oxygen-rich Ge samples were bombarded with fast electrons (E=4 MeV) at 80 °C and subjected to isochronal (100–340 °C) and isothermal (350 °C) annealing. Infrared absorption spectra were measured at room temperature. Preliminary irradiation of the samples is found to strongly enhance the development of the absorption bands in the range 600 to 780 cm⁻¹ when the Ge〈Sb,O〉 crystals are heated to 350 °C. The bands are assigned to local vibrational modes of thermal donors. It is inferred from the annealing studies that a radiation-induced complex with the local vibrational modes at about 770–780 cm⁻¹ is probably responsible for the enhanced growth of the thermal donors. Oxygen dimers are proposed as such a complex. Fiz. Tekh. Poluprovodn. 33, 1287–1289 (November 1999)     

Low-temperature photoluminescence in holmium-doped silicon

In this paper the photoluminescence (PL) of holmium-doped silicon is discussed. The silicon was first implanted with holmium ions at energies of 1–2 MeV and doses of 1×10¹³–3×10¹⁴ cm⁻², and then annealed at temperatures of 620–900 °C for 0.5–1 h. In order to increase the concentration of electrically and optically active centers, the silicon was implanted a second time with oxygen ions at energies of 0.14–0.29 MeV and doses of 1×10¹⁴–3×10¹⁵ cm⁻². Several photoluminescence lines, which are attributable to the transitions of electrons from the first excited state of the Ho³⁺ ion (⁵ I ₇) to the ground state (⁵ I ₈), were observed. The amplitudes of the most intense lines, which correspond to transitions at frequencies 5119 and 5103 cm⁻¹, decreased by more than an order of magnitude in the temperature range 4.2−78 K. The PL intensity of the holmium ions increased with increasing concentrations of the implanted rare-earth ions and oxygen. Fiz. Tekh. Poluprovodn. 33, 420–422 (April 1999)     

Monte Carlo simulation of the low-temperature mobility of two-dimensional electrons in a silicon inversion layer

The transport of two-dimensional electrons in a silicon inversion layer is determined by Monte Carlo simulation in the temperature range 4.2–40 K, where the electrical quantum limit occurs and only the lowest subband is populated. Two scattering mechanisms are taken into account: scattering by distant ionized impurities and scattering by surface roughness elements, along with their dependence on the polarizability of the two-dimensional electron gas. The mobility and coefficient of warm electrons in weak electric fields are calculated. The data are compared with previously published results. Fiz. Tekh. Poluprovodn. 31, 89–92 (January 1997)     

Oxygen and Erbium related donor centers in Czochralski grown silicon implanted with erbium

The Hall effect measurements were conducted on Czochralski-grown silicon after implantation of erbium and two-step annealing at 700 °C and 900 °C. After the first step the formation of oxygen-related shallow donors was observed at E _c in the range 20–40 meV and erbium-related donor centers at ≈E _c -70 meV and ≈E _c -120 meV. Along with the same oxygen-related shallow thermal donors and donor centers at ≈E _c -70 meV, other donor centers at ≈E _c -150 meV are formed following the 900°C anneal, instead of those at ≈E _c -120 meV. The new donor states are of particular interest because of their possible involvement in the photoluminescence process. The obtained results for erbium-implanted silicon are compared with some fragmentary DLTS data found in the current literature on the donors with ionization energies less than 0.2 eV. Fiz. Tekh. Poluprovodn. 33, 1192–1195 (October 1999)     

Effect of impurities with variable valency on the transport phenomena in a quantum well

Transport phenomena in a quantum well containing a multivalent impurity are investigated on the basis of a model of strong Coulomb correlations. It is shown that as the iron content in the quantum well increases, the Coulomb correlations grow and produce ordering in the impurity system. As a result, the scattering of 2d electrons by them should weaken, and this should result in a substantial increase in the mobility of 2d electrons. Fiz. Tekh. Poluprovodn. 31, 769–773 (April 1997)     

Ion implantation of porous gallium phosphide

The effect of irradiation by Ar ions and thermal annealing on the properties of porous gallium phosphide (por-GaP) obtained by electrolytic methods is investigated. It is shown on the basis of Raman scattering and photoluminescence data that, in contrast with porous silicon, por-GaP does not have high radiation hardness, and that thermal annealing of defects in layers amorphized by ion implantation is impeded by the absence of a good crystal base for solid-state epitaxial recrystallization processes. Data on radiation-induced defect formation and from probing of the material with a rare-earth “luminescence probe” are consistent with a mesoporous structure of the material. Fiz. Tekh. Poluprovodn. 32, 990–994 (August 1998)     

Effect of the built-in electric field on optical and electrical properties of AlGaAs/InGaAs/GaAs P-HEMT nanoheterostructures

This study is concerned with the photoluminescence spectra and electrical parameters of AlGaAs/InGaAs/GaAs pseudomorphic high-electron-mobility transistor (P-HEMT) structures with a quantum well grown at different depths L _b with respect to the surface. The samples are produced so as to make the concentration of electrons in the quantum well unchanged, as the barrier layer thickness L _b is reduced. It is established that the photoluminescence spectra of all of the samples exhibit peaks at the photon energies ħ _ω = 1.28−1.30 and 1.35–1.38 eV. The ratio between the intensities of these peaks increases as L _b is decreased. Calculations of the band structure show that variations in the spectra are due to the fact that the built-in electric field increases as the quantum well is set closer to the surface.     

Electron-hole scattering in p-type silicon with a low charge-carrier injection level

A previously proposed method for determining the parameters of electron-hole scattering in indirect-gap semiconductors is used to investigate the properties of p-type silicon. Diode n ⁺-p-p ⁺ structures were used for the measurements. The results obtained by us indicate that complete dragging of the minority electrons by the majority holes is possible, even at room temperature, in p-type material with doping levels N>10¹⁸ cm⁻³. Fiz. Tekh. Poluprovodn. 31, 833–835 (July 1997     

Photoluminescence of anodized silicon carbide

The luminescence of single-crystalline 6H-SiC plates after electrochemical etching has been investigated. The photoluminescence spectrum was found to change strongly after etching; the decay times of separate bands were determined. Just as in the case of silicon, the change in the photoluminescence could be due to the formation of nanostructures. Fiz. Tekh. Poluprovodn. 31, 315–317 (February 1997)     

Optical properties of silicon-doped (100) GaAs layers grown by molecular-beam epitaxy

The photoluminescence spectra of (100) GaAs layers, both undoped and doped with silicon, is investigated at T=77 K. It is found that along with the B-band, which corresponds to interband radiative recombination, the spectra of doped layers also exhibit a so-called Si-band located near hν⋍1.4 eV. In multilayer δ-doped structures, an additional band appears in the region hν⋍1.47–1.48 eV, which is called here the δ-band. The dependence of the energy positions, intensities, and shapes of these photoluminescence bands on the doping dose N _Si, laser excitation power, and temperature are investigated. It is shown that the Si-band is caused by optical transitions between the conduction band and a deep acceptor level (∼100 meV) connected with Si atoms on As sites. It is also established that the dependences of the shape and intensity of the δ-band on temperature and photoluminescence excitation power are identical to the corresponding dependences for the B-band. The behavior of the δ-band in the photoluminescence spectra is viewed as evidence of quantum-well effects in the δ-doped structures. Fiz. Tekh. Poluprovodn. 32, 1060–1063 (September 1998)