Table of contents

The degree of structural damage induced by chemical or ionic processes on the crystalline binary compound AB is estimated by means of X-ray photoelectron diffraction and using a model where the damaged layer A_2xB_2(1-x), out of stoichiometry, is assumed to be homogeneous and in an amorphous state. Applied to the case of acidic chemical etching of GaAs (001), the experimental angular distribution curves (ADC) matched with simulated curves obtained from crystalline ADCs give a disordered surface layer thickness and composition, d=0.6 nm and x=0.625 respectively.

The I₁^deep line and its LO phonon replicas have been studied for the first time in the photoluminescence of ZnS_xSe_1-x (0.02<or=x<or=0.125) single crystals at 2 K using excitation spectroscopy, selectively excited photoluminescence and by doping and annealing with controlled partial pressures. The Huang-Rhys parameter S, defined by the intensity ratio of the one LO phonon and no-phonon luminescence lines, increases non-linearly as the composition parameter x increases.

Zn_1-xMn_xSe (0.016<or=x<or=0.445) shows luminescence emission not only in the yellow spectral range (⁴T₁ to ⁶A₁) but also in the near infrared. The excitation spectra of the yellow and of the infrared band are compared at different concentrations x and different temperatures T. Both emission bands are connected by energy transfer. While the yellow emission is well described by a transition within the 3d shell of tetrahedrally coordinated Mn²⁺ the nature of the infrared emission is not yet clear.

The random spatial distribution of carriers in fully ionised and compensated semiconductors is investigated here. As in a previous paper by B.K. Ridley (1988) the semiconductor is divided in elementary volumes V_g whose dimensions are equal to several times the Debye length, each elementary volume being assumed to be neutral overall. The probability p( nu ) to find nu carriers in V_s is obtained in terms of a Bessel function of imaginary argument, and this function is closely approximated by an analytical expression. The results are illustrated on some examples. These deal with p( nu ) and associated probabilities, the average Fermi level (for a particular case in GaAs) and its variance, and demonstrate their dependence on compensation and on the average number of carriers in V_s.

The 1/f noise in power VMOS transistors has been measured. In the ohmic device channel the number fluctuation is comparable with that in other MOS devices but is more variable with gate voltage. In saturation, the noise and DC characteristics were measured at constant temperature using pulsed methods. Using a model of the device operation and the measured ohmic channel noise, the measured noise in saturation was compared with the calculated value. Reasonable agreement was found except for a peak just before saturation. This is ascribed to a non-uniform defect distribution along the channel.

Undoped GaInAs/zinc-doped InP structures grown by metal-organic chemical vapour deposition have been exposed to a RF hydrogen or deuterium plasma. Secondary ion mass spectrometry experiments show deuterium diffusion in both materials and the existence of a hydrogen-acceptor pairing effect in the p-type InP layer. After hydrogenation, the InP layer becomes highly resistive as a result of a strong passivation of acceptors by hydrogen. Hall effect and conductivity measurements performed on a lightly thermally reactivated InP layer indicate that the hole mobility is significantly higher than in the non-hydrogenated InP layer. This increase is attributed to a decrease of the ionised acceptor concentration under hydrogenation and is consistent with the existence of a pairing between the proton and the ionised acceptor giving rise to neutral Zn-H complexes. The relative thermal stability of Zn-H complexes in InP:Zn if compared to GaAs:Zn can be interpreted with the help of the microscopic model of these complexes, hydrogen being more tightly bonded to a phosphorus than to an arsenic atom.

A sharp IR line is observed in the low-temperature absorption spectrum of p-type InP doped with zinc when it has been passivated with hydrogen or deuterium. Because of the spectral characteristics of the line, it is attributed to the vibration of hydrogen or deuterium bonded to P atoms that are first neighbours of zinc acceptors. This consistently provides the same picture of the passivating complexes as in GaAs by replacing the As atom by the P atom. It is further argued that the microscopic structure of the acceptor complexes observed in germanium doped with zinc or beryllium when grown in a hydrogen atmosphere can be similarly explained by the formation of a Ge-H bond on the first neighbour of the Zn atom, leaving the acceptor atom tri-coordinated and neutralising one of the two holes. This explains the production of single acceptor complexes with trigonal symmetry whose electronic spectra have been analysed some time ago.

Semiconductor superlattice structures are investigated from the point of view of pulsed and steady-state photoconduction. The novel features, and they are indeed many, are associated with the non-linear carrier drift velocities versus electric field, the absorption coefficient, the anisotropic recombination kinetics and transport properties, and strong excitonic effects. The recombination problem is considered in some detail. Some of the consequences have already been observed and some new effects are predicted which could be verified experimentally.

RHEED intensity oscillation data recorded during the molecular beam epitaxial (MBE) growth of InSb are presented for the first time. The effects of changing the substrate temperature and the antimony to indium flux ratio (J(Sb₄)/J_In) are investigated. RHEED oscillations are most pronounced for antimony-rich growth, with flux ratios close to unity. Antimony-induced RHEED intensity oscillation data are also presented. RHEED oscillations can now be used to calibrate growth rates and effective flux ratios during the MBE growth of InSb.

An investigation of some peculiarities and general regularities of the pressure dependencies of the effective second-order elastic constants of some A^IIIB^V (GaSb, InSb, InAs) and group IV (Si, Ge) semiconductors with different covalent-bond ionicities has been carried out by an ultrasound method at pressures up to 82 kbar and room temperature. It was found that near the semiconductor-metal phase transition the softening of one of the transverse acoustic branches of the phonon spectrum takes place, which implies a reduction in covalency.

Magnetophonon measurements in a GaInAs-AlInAs multi-quantum well show evidence for a remote interaction with AlAs-like phonons in the barriers. The strongest oscillations come from absorption of GaAs-like LO phonons in the wells in contrast to earlier results for high carrier density heterojunctions.