A. G. Milnes

Low frequency oscillations in semi-insulating gallium arsenide†

Low frequency oscillations associated with trap-controlled moving domains in high resistance semiconductors have been studied by a number of investigators. The mechanism involved is (in increase of the capture cross section of a repulsive centre with increase in the applied electric field. Although many of the features involved have been established by experimental studies, the modelling and analysis available have so far been incomplete. The present paper shows that computer studies can make a contribution to understanding of the domain behaviour and the effects of illumination. Using a simple functional form for the capture coefficient of a repulsive centre in GaAs, the non-linear equation obtained can be shown to result in a dipole domain propagating with constant velocity for bulk material. The threshold for domain nucleation was 860 volts/cm. Domain velocities were found to increase with illumination level and applied voltage, and for the model considered ranged from 0-25 cm/sec in the dark to 125 cm...

The electrical characteristics of nZnSe—pGe heterodiodes†

The forward and reverse current-voltage characteristics and reverse-biased capacitance are described for the nZnSo-p+ Ge emitter-base diodes of heterojunction transistors. The forward diode current flow involves essentially electron injection into the Go together with loss-mechanisms of recombination of injected electrons through interface states and, probably, electron capture into ZnSo traps followed by tunnelling into interface states. In the junctions that have been fabricated, the current-voltage characteristics are dominated by the high resistivity bulk ZnSo in series with the junction, resulting in space-charge-limited flow. The reverse junction characteristics demonstrate semi-saturation, avalanche multiplication, and negative resistance. The junction capacitance is strongly frequency dependent duo to the presence of relatively deep traps, and both abrupt and linearly graded junctions have boon observed, depending on the growth technique.

ZnTe-InAs heterojunctions†

Fabrication and electrical properties of p-ZnTe/n-InAs heterojunctions obtained by interface alloying, suggesting p-i-n structure from characteristics and capacitance behavior

Impact ionization of deep-impurities (In, Ni, Au) in silicon†

Abstract Hot carrier impact ionization of carriers trapped on deep energy levels in a, semiconductor is studied theoretically and oxperimentally. The electric field dependent free-carrier energy distribution is needed to calculate changes of the impact ionization and capture rates with field. Displaced Maxwell—Boltzmann treatments are not adequate for determination of free-carrier energy distributions. The free-carrier phonon interaction constants are calculated from the low-field temperature-dependent conductivity mobilities. Monte-Carlo treatments give the high-field free-carrier energy distributions from these interaction constants. These calculations also give the dependence of drift velocity at high fields in n or p silicon with good agreement with experimental results. Impact ionization is then studied for In, Ni and Au-doped silicon under steady-state conditions, in tho temperature range 65—200°K, for field strengths up to about 104 v-em−1. From the free-carrier concentrations near breakdown condit...

An experimental study of high-field moving domains produced by deep centres in semi-insulating GaAs†

Low-frequency oscillations in high-resistance oxygen-doped GaAs are shown to involve high-field domains moving from cathode to anode. These are explained in terms of a model previously derived for field dependence of an acceptor capture cross section. The computer solutions and the experimental studies suggest that the domain velocity is proportional to the current density in the material and inversely proportional to the trap density NT-. This is consistent with physical reasoning in a gross simplification of the problem. Use of this relationship allows the temperature dependence of the domain velocity to be predicted. Experimental determination of this temperature dependence then gives the energy level of the double acceptor centre involved. From this energy level, and from TSC measurements, it is inferred that copper is the acceptor involved in domain formation in the GaAs studied.

Interpretation of scanning electron microscope measurements of minority carrier diffusion lengths in semiconductors

In SEM injection measurements of minority carrier diffusion lengths some uncertainties of interpretation exist -when the response current is non-linear with distance. This is significant in epitaxial layers where the layer thickness is not large in relation to the diffusion length, and where there are large surface recombination velocities on the incident and contact surfaces. An image method of analysis is presented for such specimens. A method of using the results to correct the observed response in a simple convenient way is presented. The technique is illustrated with reference to measurements of L n and L p in epitaxial layers of GaAs. Average beam penetration depth may also be estimated from the curve shape.

Theoretical analysis for microwave T- and π-type attenuator circuits using MESFETs

ABSTRACT Field-effect transistors in T and π configurations may be used as voltage-controlled attenuators for monolithic microwave circuit applications. Design curves are presented from which the trade-offs between attentuation range, VSWR and permissible dynamic range of the microwave signal may be considered.

Calculation of drift velocity in silicon at high electric fields

Abstract Drift velocity in n and p-type silicon is calculated using the Monto Carlo method to determine the current carrier distribution. Agreement with recent measurements for high field drift velocity is good. Carrier-lattice scattering rates for p-type silicon were determined from low field mobility versus temperature. D. Longs model was used for n-type silicon.

Thermally stimulated current measurements applied to silver-doped silicon†

Abstract The theory of thermally stimulated current in semiconductors is reviewed and experimental results for silicon are discussed. Slight variations in experimental conditions can result in vastly different thermally stimulated current curves. It is further demonstrated that experimental results accurate to 0.l°K are necessary to give useful results for energy level and capture cross section. By applying the technique to silver-doped silicon of known doping, it is possible to demonstrate reasonably good agreement between theory and experiment. However, it is concluded that, in general, for thermally stimulated current measurements extreme care is necessary if intorpretablo data are to be produced

The growth and electrical characteristics of epitaxial layers of zinc sulphide and of zinc selenide on p-type gallium phosphide†

Single crystal layers of ZnS and ZnSe have been expitaxially grown on p-type GaP using an HC1 close-spaced vapour transport system. Grown layer doping is accomplished using heavily doped source (ZnS, ZnSe) material and a zinc vapour diffusion process that reduces the number of compensating zinc vacancies. Experimental characteristics of nZnS-pGaP and nZnSe-pGaP diodes indicate dominance of the forward I-U relationship by space-charge-limited flow in the 103-104 ohm-cm ZnS and ZnSe. The reverse I-U characteristics of these devices agree qualitatively with a multistep tunnelling process but show larger than, expected reverse currents. The reverse bias capacitance is strongly frequency dependent in all devices studied. Forward injection electroluminescence was not observed from any of the nZnS-pGaP and nZnSe-pGaP devices studied.