Optical transient current spectroscopy (OTCS) is a member of the class of deep level transient spectroscopy (DLTS) techniques. Its advantage is that, unlike other DLTS techniques, it can be applied to semi‐insulating normalGaAs (which is the starting material for integrated circuit (IC) fabrication). The aim is to obtain information on deep trapping levels, which may be of fundamental interest and is certainly of practical interest since it can help in diagnosing the suitability of the material for IC fabrication. We have investigated the method using different device geometries, electrode materials, surface preparations, and normalGaAs crystals. Various “peaks” in the OTCS spectrum were identified, including EL2, the center responsible for the semi‐insulating property in undoped LEC normalGaAs . One is of particular interest, since it is a negative peak, i.e., the current increases (instead of decreasing) with time (after the sudden drop when the light ceases) until it settles at its steady‐state dark value. The amplitude of this peak was found to be much bigger with thinned sandwich normalmetal/normalGaAs/normalmetal structures than with planar electrode structures. Evidence was obtained that this peak is associated with crystal damage produced by abrasion or polishing. The current theory of OTCS due to Hurtes et al. and Martin et al. is based on the Sah et al. treatment of depletion regions. It is pointed out that it may not necessarily apply with typical electrode geometries. In particular, the model that this theory provides for negative peaks is not the only possible one. Two further models are proposed. Negative peaks could be due to an electrically neutral semiconductor model in which more majority carriers are trapped due to illumination. They could also be given by an insulator model in which the current is due to thermal release of carriers from traps that then travel a certain way before recapture.

The deep trapping levels present before ion implantation of silicon into the semi-insulating LEC GaAs starting material were investigated using optical transient current spectroscopy (OTCS). MESFET channel current deep level transient spectroscopy (DLTS) was used for the implanted material. With a silicon nitride layer used to encapsulate the GaAs for postimplantation annealing and with implantation directly into the GaAs, it was found that of seven or more deep levels seen in the semi-insulating substrate prior to silicon implantation only the level believed to be EL12 remained. On implanting through a thin Si3N4 encapsulating layer and annealing under SigN4, only EL2 was found. With a silicon dioxide layer as an encapsulant, two traps remained and two apparently unreported levels appeared.

Electrode erosion (especially anode erosion) is still an important problem for high-power vortex stabilized arc lamps. A study of the electrode erosion mechanisms has therefore been carried out in vortex stabilized arcs operating at a maximum input power of 40 kW. It was found that three factors are important in the removal of electrode material: evaporation caused by thermal loading, ablation due to time varying stresses, and corrosion resulting from the presence of impurities in the gas. It was also found that the first two factors, and hence the erosion rates, can be affected significantly by the orientation of the electrodes and the presence of an external magnetic field.

This paper reports on the successful realizationA two-dimensional lossy shunt TLM network is adapted to simulate the Maxwell field equations of a GaAs MESFET. By discretizing the channel into rectangular sections of single thickness, the new TLM technique is shown, with examples, that it can simulate the calculated electromagnetic fields of an arbitrarily doped channel section.of the first procedure.

A new two-dimensional TLM procedure incorporates non-stationary electron velocities and electric fields into the computation of electromagnetic fields in submicron GaAs samples. An example demonstrates the transient electromagnetic field response to a short electric field pulse.