Table of contents

The state of the current understanding of hydrogen in elemental and compound semiconductors is reviewed. The results of new experimental and theoretical studies of the microscopic structure of acceptor-hydrogen and donor-hydrogen complexes are presented. Questions regarding hydrogen tunnelling in some of the acceptor and donor complexes in elemental semiconductors, as well as the problem of electronic states of isolated hydrogen, are discussed in the light of the most recent experimental findings. Also, some promising areas of future research are indicated.

Isothermal capacitance transient spectroscopy (ITS) has been applied to study p-type Ti-doped GaP at temperatures as high as 430 K. A deep level with an apparent activation energy of 1.15+or-0.06 eV has been detected and identified as the Ti³⁺/Ti⁴⁺ donor level. This assignation is based on the optical photoneutralization threshold of 0.92+or-0.02 eV, which agrees with previous photoelectron paramagnetic resonance (EPR) results and the agreement between the level concentration and secondary-ion mass spectroscopy (SIMS) measurements of Ti content.

A description of GaAs Hall generators, formed in a n-type GaAs epitaxial layer grown on a GaAs semi-insulating substrate by the liquid-phase epitaxial technique, is given. Indium-doped semi-insulating GaAs substrate is used to produce Hall devices with a high sensitivity of 130-160 V A^-1T^-1 and linearity of <or=1.5% by mitigating effects from the transition layer. These devices have a high temperature stability; they can operate stably at temperatures up to 200 degrees C.

A method for self-consistent calculation of the energy structure of semiconductor quantum wells with in-plane magnetic field that takes into account nonuniformity of material parameters is proposed. Numerical results for GaAs quantum wells in Al_xGa_1-xAs bulk are given for the magnetic field range 0-15 T and briefly discussed. An unusual nonmonotonic dependence of conduction band edge on magnetic field is observed.

X-ray photoelectron spectroscopy (XPS) measurements on silicon surfaces treated by HF gaseous cleaning are described. Various cleaning recipes, which essentially differ by the amount of water present during the reaction, were studied; the composition of the silicon surface was measured in terms of monolayer coverage of oxygen, fluorine and carbon. These gaseous-cleaned surfaces are compared with the silicon samples deglazed by using an aqueous HF bath. The F(1s), O(1s), Si(2p), C(1s) photoelectron lines were monitored, and concentrations determined as usual by integration of the lines after removal of a nonlinear background. The F(1s), C(1s) and Si(2p) lines were decomposed into several components corresponding to different chemical bonds. The results show that the amount of fluorine is directly correlated with the amount of oxygen: fluorine concentration increases slightly with oxygen concentration from 0.2 monolayers (ML) up to 0.7 (ML); most is in a O-Si-F bonding state. For more aggressive etching, leaving less than one monolayer of oxygen, the Si-F bond becomes predominant. The ratio of the SiF to OSiF concentrations is a significant indicator of the deoxidation state of the surface. Hydrophobicity of the water appears in the range of 25% Si-F bonds. With very aggressive etching processes, 67% Si-F bonds and 33% O-Si-F bonds are reached and the total amount of fluorine drops below 0.3 ML. For comparison, only Si-F bonds are observed after wet etching in a dilute HF bath without a rinse with a much lower fluorine concentration. The balance between Si-F and O-Si-F remains stable and seems to be representative of the surface states provided by the etching process.

The authors report the fabrication of n-type GaInP/Ga_xIn_1-xAs lattice-matched (x=1) and strained (x=0.85) two-dimensional gas field-effect transistors grown by low-pressure metallorganic chemical vapour deposition on GaAs semi-insulating substrates. The GaAs-GaInP devices demonstrate excellent operational performance at low temperature, due to the absence of deep traps in doped GaInP layers. The extrinsic transconductance is 163 mS mm^-1 at 300 K and 213 mS mm^-1 at 77 K. The threshold voltage of the devices biased in the dark at V_ds=3 V was -3.34 V at 300 K and -3.38 at 77 K. Microwave measurements revealed cut-off frequencies f_T of 17.8 GHz and f_MAX of 23.5 GHz.

Using ab initio pseudopotentials the authors calculated the electronic structure of the Si₆/(Si_0.5Ge_0.5)₆ superlattices strained to Si, Si_0.75Ge_0.25 and Si_0.5Ge_0.5 (001) orientated substrates. They found that none of these materials displays direct gaps. They also calculated the valence band offsets of the Si/Si_0.5Ge_0.5(001) interface for different strain configurations and found them not to be simply one half of those of the Si/Ge interface for the same strains.

The influence of the polarization of the IR radiation on the magneto-optical spectrum of the parabolic quantum wells is discussed. It was shown, using the approach developed by Brey et al. (1989) that tilting of the magnetic field leads to the strong dependence of the cyclotron spectrum on the polarization of the light in the plane of the quantum well.

The magnetic field dependence of diode laser emission has been investigated in Pb_1-xMn_xSe diodes with low MnSe contents (x<or=0.02). The values of the effective g-factor of holes and conduction electrons have been determined. The results indicate that there is a major contribution from the exchange interaction between the band carriers and localized Mn magnetic moments to the g-factor of holes. The exchange interaction parameters have been found to be A=-0.08 eV and B=0.02 eV for the valence and conduction bands respectively.

For the first time a diamond anvil cell high-pressure technique has been used for far-infrared laser magneto-optical experiments. A shallow-deep transition was observed for shallow sulphur and silicon donors in high-purity GaAs at pressures of 25 and 30 kbar respectively. This transition is similar to that previously observed at 9 kbar for Ge residual donors. The deduction of A₁ symmetry for the deep electronic states involved results from the observation of anticrossing effects. Large 'chemical shifts' between deep states of different impurities provide evidence for their strong localization. Fast electron capture onto these deep states at low temperature demonstrates their non-DX-like character. Present results and similar experiments with InSb show that three kinds of donor states, shallow, deep A₁ and DX-like, are generally expected to exist in III-V compounds and alloys.

The optical orientation in semimagnetic semiconductors is studied. It is shown that in the absence of an external magnetic field the nonequilibrium photomagnetization is certainly greater than the equilibrium photomagnetization, connected with cooling of the magnetic ions by the oriented electrons.

A thorough photoluminescence (PL) investigation of heavily Be-doped (up to a maximum of approximately 3*10¹⁹ atoms/cm³) chemical beam epitaxy (CBE) grown InP layers showed the presence of two prominent emissions related to Be, one involving simple isolated Be acceptors (Be_In^-) and the other a deep-level (DL) band behaving like a pseudo donor (D)-acceptor (A) pair-like transition. From their identical values of activation energies for luminescence quenching ( Delta E approximately 40+or-2 meV), the participation of a simple Be_In^- acceptor (A) and a deep donor (D) of the type (Be_In^--Be_i⁺)⁺ (where Be_i stands for a doubly positively charged interstitial Be) have been predicted for the pseudo D-A pair of the DL emission. The possible presence of such centres is suggested as an explanation for the observed abnormally low acceptor efficiency (only 20 to 25%) of Be when doped heavily in InP.

Thermal oxidation of GaSb has been carried out and the oxide characteristics have been studied in detail. XPS analysis reveals that this oxide is composed of both Ga₂O₃ and Sb₂O₃. The oxide has high DC resistance and excellent breakdown strength. C-V characteristics of the Al-oxide-GaSb MIS structure are also presented.

A chemical deposition technique, much simpler and more versatile than previously reported and capable of yielding good quality SnS films of thickness up to approximately=1.2 mu m under a choice of deposition conditions, is presented. The as-prepared films are polycrystalline with p-type dark conductivity in the range 10^-5-10^-4 Omega ^-1 cm^-1 for the thicker ( approximately 1 mu m) films and showing a photocurrent to dark current ratio of 5-10 under 500 W m^-2 tungsten halogen illumination. The optical transmittance and reflectance spectra and the photocurrent response curves of a series of SnS samples are explicitly presented to provide insight into possible applications of these films.

BSF solar cells are fabricated using B-doped wafers cut from Czochralski Si(100) single crystals. The effect of unintentional impurities of oxygen and carbon atoms on the solar cell performance parameters have been studied. The presence of carbon atoms gives an improvement in all parameters, particularly the short-circuit current whereas oxygen produces an adverse effect.

Very significant enhancements in photoelectrochemical activity, particularly the photocurrent (short circuit current), have been noticed when preheated (up to approximately 42 degrees C) electrolyte is used in PEC solar cells comprising a single crystal n-WSe₂ photoelectrode with I^-/I₃^- electrolyte. Current enhancements ranging from two to five times have been observed for different n-WSe₂ photoelectrodes. It has been shown that this enhancement, although obtained through electrolyte heating, is a room temperature phenomenon and is invariably present for all the n-WSe₂ photoelectrodes employed in the present investigation. Measurements of the various characteristics of the electrolyte and the crystal surface/interface reveal that the only feature which undergoes noticeable change is the flat band potential. Mott-Schottky plots reveal that a representative change in flat band potential is a shift from -0.41 V (native electrolyte) to -0.84 V (preheated electrolyte). The most likely cause of the enhancement is thought to be the formation of other polyiodides such as I₄^2- and I₅^- during cooling of the heated electrolyte and their consequent adsorption onto the crystal surface. This leads to passivation of surface states through the formation of complexes involving W⁴⁺ and I₄^2- and/or I₅^-. Such a passivation will reduce the density of recombination states leading to the observed enhancement in the photocurrent.

Recent applications of simple electron-counting arguments have proved useful in explaining the relative stability of the various surface atom configurations occurring during MBE growth at III-V semiconductor surfaces. Electron-counting considerations impose constraints upon the stable chemisorption of deposited atoms, requiring that growth proceeds via a well-defined sequence of stable chemisorption stages. A simple way of incorporating this effect into Monte Carlo simulations of III-V MBE growth is presented. It is shown that the incorporation of electron-counting constraints into a simulation of growth of the GaAs (001) 2*4 system has a significant effect upon the degree of layer-by-layer growth and upon the surface roughness of the simulated grown surface.