H.K. Henisch

On the mechanism of ovonic threshold switching

Abstract By means of a ‘rare double pulse technique’, it is shown that the mechanism of threshold switching in thin chalcogenide glass systems is essentially non-thermal in character. The switches were prepared by evaporating layers of approximately 1μ thickness on to polished graphite electrodes, using Te 40 As 35 Ge 7 Si 18 as starting material. Polarization effects and polarization reversals on switching have been observed which are in qualitative harmony with a space charge theory of threshold switching previously advanced, at any rate in the low-temperature range (−78°C to +20°C). A non-polar electronic process is evidently operative above room temperature. The magnitude of the perturbation caused by heat dissipation in these systems is also assessed.

The interpretation of ohmic behavior in semi‐insulating gallium arsenide systems

The paper is concerned with the interpretation of measurements on semi‐insulating gallium arsenide and, in particular, with the evaluation of effective bulk resistivities from the results of observations on two‐electrode systems. These observations tend to be dominated by injection effects, even when the contacts used are nominally of low resistance. Order‐of‐magnitude errors can arise from this cause, even though the specimen may appear to exhibit ohmic behavior. Carrier concentration, field‐ and space‐charge contours are calculated on the basis of a model within the realm of a small‐signal theory, for conditions which correspond to lifetime, relaxation, and hybrid operating regimes.

Switching in organic polymer films

Abstract In this paper we discuss threshold switching effects in thin films of polymethylmethacrylate on molybdenum, silver, copper, graphite, Nesa and Nesatron substrates, using counterelectrodes of pyrolytic graphite. The similarities to corresponding phenomena in multicomponent chalcogenide alloys point to inherently common mechanisms. Lateral variations in switching characteristics are discussed in terms of trap distribution statistics.

Minority‐carrier injection into relaxation semiconductors

This paper deals with the injection of minority carriers, through a contact or junction, into materials of high resistivity and low carrier lifetime. Semi‐insulating III‐V compounds and many amorphous materials come under this heading. Since the macroscopic transport equations cannot be analytically solved, it is necessary to resort to numerical computation. Recent work along those lines has shown that the nature of the assumed boundary conditions has a profound effect on the results. The relationships are illustrated by concentration and potential contours of semi‐infinite and p‐i‐n systems, with various ratios of lifetime to dielectric relaxation time.

Space‐charge controlled conduction in thick metal‐insulator‐metal barriers

Numerical solutions of the (field and diffusion) transport equations yield energy and concentration contours for thick M1‐I‐M2 (metal‐insulator‐metal) barriers, and their appropriate current‐voltage relationships, with and without traps. Traps must ordinarily be expected in such films, and it is shown that they result in a curvature of the barrier profile, which exercises a controlling influence over I‐V characteristics in the forward direction.

Minority carrier exclusion

Abstract The paper deals with a current-controlled non-equilibrium process, whereby the influx of minority carriers into a semiconducting material is smaller than the rate required for normal conduction in the undisturbed, homogeneous bulk. It is shown, within the framework of a “small signal theory”, how the corresponding concentration and field contours depend on the carrier lifetime, the mobility ratio and the current composition contact characteristics (via the exclusion ratio). The departures from electronic equilibrium can lead to a total resistance increase or a decrease, depending on the detailed combination of parameters.

Drift-diffusion theory of symmetrical double-junction diodes

Abstract Using numerical methods, we have calculated the current-voltage characteristics, energy contours and carrier distributions of a symmetrical double junction diode ( n + nn + and n + pn + ). It is found that the I-V characteristics at low currents and voltages depend greatly on the doping concentration of the base region; at hihg currents, they do not. In that regime, the characteristics bunch together, and can be approximated with remarkable fidelity by the Mott-Gurney law for space-charge controlled conduction in solids. Characteristics are presented for different impurity densities and base widths.

Photo-stimulated radiation dosimetry

Abstract A method is described which permits photo-stimulated polarization transients in single crystals of ZnS to be used for the measurement of u.v. or X-ray dosages previously received by the specimen. The response is accurately linear over three decades of dosage and, with present instrumentation, dosages as small as 0·01 μ W-sec/cm2 can be detected.

Current‐controlled nonequilibrium processes in semiconductors

The paper gives a unified overview of the four nonequilibrium processes (injection, exclusion, extraction, accumulation) which occur when current is passed through a semiconductor boundary. Concentration and field contours are provided for the situations which occur in semiconductors, as well as local resistivity versus current relationships for both directions of current flow.

Single‐carrier space‐charge controlled conduction

Single‐carrier space‐charge controlled conduction in metal‐insulator‐metal structures has been studied. The dc J‐V characteristics have been calculated over an extended range of current for insulator films of different thicknesses with and without traps. It is found: (i) The current is proportional to voltage at low currents, the proportionality factor depending on the injecting contact carrier concentration, insulator thickness, and trap density. (ii) At moderate currents, the J‐V characteristics can be approximated only over a limited range of currents by a power law with the exponent n depending on the injecting contact carrier concentration, insulator thickness, and trap content. (iii) At high currents the conduction is ohmic and the characteristics are identical for insulators with or without traps. The special case of identical carrier concentrations at both contacts is also discussed. It is found that in this particular case the square law in voltage and the cubic dependence in thickness become onl...