Injected carrier flow in a semi-insulator containing a density gradient of a deep impurity

Abstract

Double injection theory in semi-insulators (semiconductors) containing deep acceptor impurities and a small density of shallow donors is extended to include the effects of gradients in the deep impurity density. The space-charge neutrality based solutions for the square-law region show strong dependence on the direction of injection with respect to the density gradient. The intersection point between the ohmic region and the square law region is shown to shift to lower voltages when hole injection takes place at the highly doped end of the π-type device. For electron injection at the acceptor-type trap rich end, a condition of single injection is approached and the double injection model does not hold. Experiments with semi-insulating silicon p + πn + structures, where the π region contains a diffused gradient of indium as the deep acceptor, confirm the main conclusions of the theory.