Filamentary Injection in Semi-Insulating Silicon

Abstract

Double injection in semi‐insulators causes a negative resistance regime. The voltage across the bulk material drops from the value necessary for the onset of negative resistance to a value that may remain fairly constant while the current increases by an order of magnitude or more. This region exists because the double‐injection occurs initially along a filament in the bulk material. Its current growth is marked by a constant voltage region followed by an I vs V^1.5–1.9 relation, somewhat similar to the V² region predicted by Lampert and others. The existence of filamentary breakdown has been inferred by very indirect evidence up to now, although Ridley has shown that it might be expected from considerations of energy. The present study shows the development and growth of double‐injection filaments in semi‐insulating silicon, by photographing them with their own recombination radiation. The silicon used was approximately 10⁴Ω·cm at 77°K and contained 6×10¹⁶ cm⁻³ indium atoms as the deep acceptor responsible for the semi‐insulating character. A theoretical model is presented for the current density within the filament. The current densities observed by densitometer studies of the recombination radiation photographs are in reasonable agreement with this model. Experimental V−I characteristics are also predicted by the theoretical study.