Properties of Gallium Arsenide Double-Injection Devices

The characteristics of identically fabricated double-injection devices made from oxygen-doped and chromium-doped bulk gallium arsenide are investigated. All these devices exhibit a current-controlled negative resistance once a threshold voltage is reached. The oxygen-doped devices and the thin chromium-doped devices (less than 3 mil) exhibit an abrupt current-controlled negative resistance followed by filamentary current conduction; this behavior is caused by double-injection transit-time effects. The thick chromium-doped devices (greater than 3 mil) exhibit a gradual, current-controlled negative resistance unaccompanied by filament formation; this behavior is due to excessive power dissipation resulting from high threshold voltages. The characteristics of the double-injection oxygen-doped devices show that a current saturation occurs in the prebreakdown region under certain conditions. The characteristics of the chromium-doped devices exhibit no such current saturation, only superlinear behavior. It is established that the oxygen devices have a threshold voltage for breakdown which is proportional to device length squared and that the chromium devices generally follow a similar law. Other evidence supporting the trapping barrier postulated by Lampert is also given. Filamentary conduction in the postbreakdown region is investigated by direct recording of the recombination radiation on infrared film. It is established that impedance variations and secondary breakdowns observed on the voltage-current characteristic are caused by movement of the filament position between the two injecting contacts. Filament position instabilities under cyclic excitation are observed and these effects are linked to a localized increase in the trapping barrier caused by heating along the filament site. Photographs of the recombination radiation emanating from both contacts establish the two-carrier nature of the postbreakdown filamentary state.