Table of contents

Infrared absorption measurements have been made of the LVMS of ⁹Be acceptors in MBE GaAs and ¹⁰B and ¹¹B acceptors in ion-implanted Si. The former line is asymmetric, while the latter lines occur as anti-resonances in the electronic continuum. Following 2 MeV electron irradiation to effect electrical compensation, symmetrical lines were observed. The new data for GaAs:Be explain an apparent anomaly relating to LVM line strengths in hydrogen-passivated material.

Deep electron states in undoped GaAs grown by the liquid-encapsulated Czochralski (LEC) method using a pyrolitic boron nitride (PBN) crucible were investigated by DLTS and Hall measurements. Six electron traps with activation energies ranging from 0.14 to 0.82 eV were detected. One of these traps, with an energy of 0.27 eV (EL6), was reduced in concentrations by more than an order of magnitude by an 800 degrees C heat treatment for 1 h. Temperature-dependent Hall measurement on as-grown material indicated that the 0.27 eV state plays an important role in the decrease of the resistivity of undoped crystals that have a low concentration of carbon impurity. The effect of gamma irradiation on the annealing properties of the traps was also demonstrated.

Deep centres in neutron-transmutation-doped semi-insulating GaAs grown by the liquid-encapsulated Czochralski (LEC) technique were studied using the photoluminescence technique. Two photoluminescence bands, PL1 and PL2, were observed at 1.26 and 1.0 eV from the band edge, respectively. The Ge-photoluminescence band is also observed. The Franck-Condon shift was estimated for PL1 and PL2 by utilising the temperature dependence of the linewidth and the configuration coordinate model. The PL1 atomic structure is speculated to be more complex than that of PL2. Both PL1 and PL2 are related to the impurities introduced by the neutron transmutation doping.

D^- states (i.e. the states formed by a neutral donor, D⁰, binding an extra electron), D⁰ interexcited state transitions (i.e. n to m where the principal quantum numbers n, m are greater than 1) and cyclotron resonance are all observed simultaneously in the far-infrared spectrum of n-GaAs and n-InP. This observation constitutes the first unambiguous identification of D^- states in a compound semiconductor. D^- states have been observed in seven GaAs and two InP samples. A chemical shift is observed, but no central cell splitting is found even at the largest available fields (i.e. 24 T). D^- states are studied under a variety of experimental conditions such as hydrostatic pressure, temperature and electric field bias. The application of hydrostatic pressure strongly enhances the D^- intensity in VPE InP, but not in VPE GaAs. Effects attributable to the formation of D^- complexes occur in GaAs when the temperature is reduced to 2 K. The intensity of the D^- transition increases markedly with increasing electric field bias. Divergence between theory and experiment is evident when the dimensionless magnetic field parameter, gamma , exceeds unity, indicating the inadequacy of existing variational calculations in this regime. D^- triplet and singlet transitions are tentatively identified in n-InSb.

The subband depopulation due to a magnetic field in a quasi-one-dimensional GaAs-AlGaAs heterostructure system is examined in the framework of an infinite box potential. The results are compared with calculations using a parabolic confinement and experimental results from Shubnikov-de Haas oscillations. The two models give good agreement with the experimental values in different regions of the channel widths.

A thin spin-on glass film has been used as a cap during alloying of concentric Au-Ge/Ni ohmic contacts to n-GaAs. Both furnace and scanned electron beam (SEB) capped alloyed contacts exhibit approximately a factor of 4 to 5 times lower specific contact resistance and a significantly improved surface morphology compared with that of uncapped alloyed contacts. Electrical measurements of Schottky diodes formed on GaAs surfaces which have been exposed to the alloying process reveal that the spin-on glass capped surfaces are better preserved than the uncapped surfaces. SEB alloyed contacts (both uncapped and capped) exhibit good resistance to degradation after 1000 hours of aging at 200 degrees C. Furthermore, Schottky diodes formed on capped SEB alloyed surfaces exhibit the least change in their electrical parameters during aging at 200 degrees C.

Copper(I) oxide films were prepared on copper substrates by exposing them to solutions containing Cu²⁺ ions, and it was observed that the photoresponse of these films electrodes in a photoelectrochemical cell is both n- and p-type. However, it was observed that the n-type behaviour of these film electrodes could be enhanced and the p-type behaviour could be reduced by adjusting the pH of the solution in which the oxide films had been prepared. The simultaneous existence of spatially separated n- and p-type regions in the Cu₂O film is suggested as the possible reason for these observations. The anodic oxidation of copper was considered to be the origin of the p-type regions while the n-type regions were considered to be the result of the cathodic deposition of Cu₂O.

The author has used the complete neglect of differential overlap method to calculate the binding energy of atomic hydrogen of the two chemisorbed phases on Si (100) surface, namely monohydride phases and dihydride phases. A 59-atom molecular cluster is used to simulate the crystalline Si (100) surface. He found that the binding energy of hydrogen in dihydride phases is larger, and the Si (100) surface is contracted in dihydride phases.

This paper describes the use of photoluminescence measurements to characterise the processing of annealed Si⁺ implanted GaAlAs/GaAs MQW structures. The photoluminescence band-edge emission gives a direct measure of the progress of the mixing of the MQW material and the optical wave confinement factor. In addition we have observed an emission from deeper radiative defects which correlates with the waveguide attenuation for long anneal times.

For a single quantum well (SQW), interference of light from the well and the top surface plays a crucial role in determining the electroreflectance. The lineshape for the N=1 interband transition is a linear combination of the first differential of the real and imaginary parts of the QW dielectric susceptibility. This mixture is determined by the phase change for light making the round trip from the top surface, to the wall and back to the top. The authors change this phase factor experimentally (on a GaAs/AlGaAs SQW) by varying the angle of incidence and observe lineshape evolution in good agreement with predictions. Least-squares fitting to the spectra, using a QW dielectric susceptibility comprised of contributions due to light- and heavy-hole excitons, suggests Lorentzian broadening dominates at low temperature and Gaussian at higher temperatures. These conclusions are reached by not only fitting individual spectra, but additionally by examining which broadening mechanism gives the better description of the lineshape evolution with angle of incidence. They observed an unexpected difference between spectra taken with TE and TM polarised light and suggest that this may be because of a thin film of intermediate reflective index on top of the sample, rather than any property of the QW or the cladding, This thin film may ultimately limit the accuracy to which electroreflectance spectra can be modelled.

Contact and proximity ablation experiments on 1.1 mu m thick layers of Hitachi PIQ-13 polymide using chrome-on-quartz masks and ArF excimer laser radiation of 193 nm wavelength and fluence of 0.2 J cm^-2 were performed in vacuum and air respectively. To examine the deposition behaviour of ablation residues, a constant nitrogen or oxygen gas stream at pressure of 3.5 bar corresponding to a flow rate of 0.5 l s^-1 was directed through a proximity gap of about 5 mu m. In both cases an orientation of the ablation residues in the direction of the gas flow was observed. Thus ablation residues were minimised in exposed areas. Complete removal of ablation debris was achieved within 1.5 min in an ultrasonic bath. A structure resolution of approximately 0.3 mu m could be obtained.

The authors determine the electric-field-induced spin splitting of the electron subbands on the surface of narrow gap HgCdTe from measurements of the oscillatory magnetoconductivity and cyclotron resonance. The coalescence and crossing of the Landau levels in the Shubnikov-de Haas oscillations is analysed in terms of the model developed by Bychkov and Rashba (extended to include nonparabolicity). Together with the resonance data it allows them to obtain the dispersion E₀^+or-(k/sub ///) of the electrically spin-split ground state subband. The experiments provide for the first time a number to be compared with sophisticated subband calculations.

Computer simulation of the (400) X-ray double crystal diffraction rocking curves is presented for a superlattice structure. The model used is a combination of the Takagi-Taupin method and Abeles matrix method for the calculation of reflectivities from the substrate and superlattice periods respectively. Computer simulation of experimental rocking curves of InGaAs/GaAs strained-layer superlattices (SLS) on (100) GaAs substrate obtained from this method has been compared with those obtained from two other models based on kinematic and dynamic approaches.

The quantum efficiency of field-assisted transmission-mode GaAs photocathodes has been calculated. The results show that supplying an electric field across a photocathode is an efficient way to greatly increase the quantum efficiency of transmission-mode GaAs photocathodes.

The dilute delta -doping layer, grown by molecular beam epitaxy (MBE), is an ideal system to study activated transport and the metal-insulator transition (MIT) in two dimensions (2D). The authors show the 2D anisotropy of magnetotransport with the magnetic field parallel and perpendicular to the doping plane. They observe a distinct negative magnetoresistance caused by quantum interference in the hopping transport.