Table of contents

An outline of infrared localized vibrational mode absorption spectroscopy relevant to silicon impurities in GaAs is presented. Absorption lines from Si_Ga donors, Si_As acceptors, Si_Ga-Si_As pairs, Si_Ga-V_Ga (Ga vacancy) pairs and a complex Si-X (involving Si_As and V_Ga) have been identified as well as lines from Si_Ga-Cu_Ga, Si_Ga-H, Si_As H and Si_Ga-B_As pairs. These observations are related to the electrical properties of n-type Bridgman, liquid-encapsulated Czochralski and molecular beam epitaxial (MBE) (001) GaAs, and to p-type liquid phase epitaxial and MBE (111)A layers. The discussion relates to dynamic site switching, effects due to counter-doping with shallow acceptors, the solubility of silicon, and DX behaviour observed in homogeneously doped material and proposed for delta -doped MBE (001) layers. The major problem is to understand the processes that limit the maximum carrier concentration that can be achieved in n-type crystals.

The surface capture velocity is introduced as a new parameter which should be used to describe the capture and emission processes of carriers in quantum wells. A calculation of the surface velocity is presented for deformation and polarization types of carrier interaction with optical phonons. The dependence of the capture velocity on the free carrier kinetic energy and/or quantum well parameters is investigated. Application of the theory is illustrated with the capture of holes in Si/Si_0.8Ge_0.2/Si quantum wells.

We report a perturbative-variational calculation on the effect of magnetic and electric fields on excitons in parabolic quantum dots. The effects of electric and magnetic fields on 1 s exciton energy and oscillator strength are investigated. The competition between the confinement and correlation effects on the one hand, and the external field effects (electric and magnetic) on the other hand, is also discussed.

We consider the effect of image forces, arising due to a difference in dielectric permeabilities of the well layer and barrier layers, on the energy spectrum of an electron confined in a rectangular potential well under a magnetic field. Depending on the value and the sign of the dielectric mismatch, image forces can localize electrons near the interfaces of the well or in the well centre and change the direct intersubband gaps into indirect ones. These effects can be controlled by variation of the magnetic field, offering possibilities for exact tuning of electronic devices.

The absorption coefficient of donor impurities located at the centre of a quasi-1D GaAs quantum well wire is calculated as a function of photon energy for different wire widths. The influence of a uniform magnetic field, applied along the axis of the wire, on the optical spectrum associated with the electron transition between the donor ground state and the first conduction subband, the bound-to-band transition, is also investigated.

Inelastic scattering of 10.6 mu m CO² laser radiation by free carriers has been studied in p-type Ge for a wide range of hole concentrations (5*10¹⁵-5*10¹⁷ cm^-3). Scattering by unscreened single-particle excitations as well as by collective ones was observed. It is found that single-particle scattering arises from fluctuations of the quadrupole moment of heavy holes. The theory for this scattering mechanism in the quantum case, which explains the shape of the Raman spectrum and the measured scattering efficiency for the sample with lowest concentration of holes is presented.

Deep levels created by hydrogen and oxygen plasma treatment in n-type Si substrates are investigated using deep-level transient spectroscopy (DLTS) in the temperature range 77-300 K. It has been established that both types of plasma treatment at temperatures ranging from 20 to 300 degrees C generate deep levels in the Si bandgap which can be connected with hydrogen- or oxygen-containing complexes and divacancy defects. The defects are situated in the Si substrate within about 1 mu m from the Au-Si interface.

We have studied the behaviour of TO phonon modes in In_xGa_1-xAs_yP_1-y grown on GaAs (100) and (111)A substrates by means of Raman scattering. It was found that the small peak which appeared between the GaP-like LO₁ and InP-like LO₂ modes is due to the GaP-like TO₁ phonon mode. The mode calculation based on the cell isodisplacement theory was in good agreement with the experimental results.

We report the first observation in CdTe of a reversible photoluminescence spectral transformation between the Z-luminescence system and the 'self-activation' band by high-temperature treatments and aging at room temperature. We propose that some residual impurity is responsible for both Z-recombination (isolated impurity) and the self-activation band at approximately 1.45 eV (complex with a shallow donor). There is reason to believe that a key to understanding the compensation mechanism is the formation of impurity complexes consisting of the shallow impurity (donor or acceptor) and the Z centre.

The Stark-ladder transitions in a type-II (GaAs)₈/(AlAs)₈ superlattice are investigated under various uniform electric fields by using electroreflectance spectroscopy. The electroreflectance spectra suggest the existence of a Stark-ladder transition from the heavy-hole state in the Gamma valence band to the electron state in the X conduction band. The Stark ladders of the X miniband show a strong mixing with the Gamma miniband. The experimental data from electroreflectance measurements are compared with a theoretical calculation based on the tight-binding method, and reasonable agreement is found.

A modification of liquid-phase epitaxy has been developed to grow epitaxial layers by ultrafast cooling ( approximately 10²-10³ degrees C s^-1) of solutions supersaturated beyond the critical value. Epilayers of GaAs and metastable (Ge₂)_x(GaAs)_1-x solid solutions were grown on Si (111) substrates, and specific features of the crystallization process were investigated. It is shown that, for GaAs layers to grow on Si, Ga and Sn solutions must be supercooled far below the critical point in the initial growth stage. The composition, structural perfection and luminescence properties of the grown layers have been studied.

Transmission electron microscopy (TEM), capacitance-voltage (C-V), and photoluminescence (PL) measurements have been performed to characterize the properties of edge delta-doped and centre delta-doped Al_0.27Ga_0.73As/GaAs single quantum wells grown by metalorganic chemical vapour deposition. Direct observation of the Si delta-doped layer in GaAs quantum wells has been achieved by TEM, and the results of the C-V profiles indicate that the full width half-maximum value of centre delta-doped quantum wells is much narrow than that of edge delta-doped quantum wells. Temperature-dependent PL spectra of centre delta-doped quantum wells show the strong luminescence attributed to the Fermi edge singularity caused by enhanced confinement of carriers by the quantum well.

Transparent conducting cadmium oxide (CdO) films have been deposited by spray pyrolysis. The film thicknesses have been determined using Rutherford backscattering spectrometry. X-ray diffraction measurements show that the films are polycrystalline with a preferential orientation along the (111) diffraction plane and the lattice parameter has been calculated. The dislocation density and strain have also been evaluated. The films possess a transmittance of about 75% in the visible and near-infrared region. The refractive index is found to vary between 1.68 and 2.84 in the wavelength range 500-1500 nm. The values of indirect and direct bandgaps obtained are 1.98 and 2.32 eV respectively. Hall effect measurements have been carried out in the temperature range 304-349 K. Resistivity, carrier concentration and mobility of the films at room temperature have been evaluated as 6.6*10^-5 Omega m, 1.4*10²⁵ m^-3 and 0.68*10^-2 m² V^-1 s^-1 respectively. Thermoelectric power values from thermoelectric power measurements carried out in the temperature range 304-376 K have been found to be about 19.7-89 mu V K^-1. Laser damage studies performed at a wavelength of 1.06 mu m indicate that the films possess a damage threshold density of about 2.37*10⁴ J m^-2.

For part I see ibid, vol.9, p.1666 (1994). Total growth rate and composition data of amorphous Si_1-(x+y)Ge_xB_y thin films grown from silane, germane, diborane and helium-hydrogen gas mixtures at 500 degrees C and 0.2 Torr are the subject of a closer examination. Data are interpreted against the background of the 'three partial rates' model taking into account the results published in part 1. Besides the partial pressures of the source gases, total pressure and temperature, the total atom number per cm³ of the thin film also controls layer growth rate. Additional silicon deposition is principally caused by the presence of germane or diborane in the gas phase. At a deposition temperature of 500 degrees C, however, germane does not cause additional silicon deposition, but diborane does. In the binary Si/Ge and Si/B systems the rate of additional silicon deposition depends on both the partial pressure of the respective source gas and the composition of the thin film. In the ternary Si/Ge/B system, however, the partial growth rate of additionally deposited silicon remains constant as long as, for instance, the diborane partial pressure is unchanged, though the boron content of the film is varied by a variation of the germane partial pressure.

This brief report describes the results of an investigation into the growth of CdSe_xS_1-x crystallites in a glass matrix. The effects of crystallite growth temperature upon the crystallite sizes and stoichiometry, as determined by photoluminescence and Raman spectroscopies, are discussed. A novel effect is reported whereby the sizes of the semiconductor crystallites can be controlled by altering the initial doping level of the glass.

We investigate the electronic noise and impedance field of submicron n⁺nn⁺ diode generators when loaded by an external resistance in the framework of a Monte Carlo and a hydrodynamic simulative approach. We observe a long-time oscillation of the correlation function of the voltage drop fluctuations between the resistor terminals. The oscillations are in turn responsible for a peak in the noise power-spectrum which is caused by the spontaneous formation of electron accumulation layers. The drift of these layers through the n-region is monitored for biasing conditions above threshold for microwave generation. The frequency of the noise peak is shown to correspond to the highest generation frequency for the given load resistance. The noise power-spectra calculated for three different values of the load resistance are used to obtain the small-signal and noise characteristics of the intrinsic unloaded diode. The parallel hydrodynamic calculation of the diode impedance spectrum is found to compare well with the results obtained from the noise analysis of the Monte Carlo simulation.

Calculations using the self-consistent unrestricted Hartree-Fock-Roothan method are carried out in the MNDO approximation for a cluster of 35 host atoms of cubic SiC with a boron impurity. The equilibrium geometry and the hyperfine and quadrupole constants are obtained and compared with experimental values. The computed parameters reveal the main features of boron impurities in SiC.