INTERBAND AND IMPURITY BREAKDOWN IN A SEMICONDUCTOR WITH AN IMPURITY BAND IN A HIGH-ELECTRIC-FIELD

Hot electron kinetics and electric breakdown in a semiconductor with a band of delocalized impurity states are investigated theoretically for the first time. We consider the case when the impurity band is separated from two allowed bands of the crystal by gaps of forbidden states. Contributions to the kinetics from all three groups of carriers in the conduction, valence and impurity bands are taken into account including changes in carrier concentrations due to impact ionization in a high field. It is shown that a new combined overheating mechanism of S-type negative differential conductivity can take place in the system which is connected with simultaneous changes in the carrier concentrations and mobilities. It is predicted that in some cases the current-voltage characteristics of the system can have two S-shaped parts. The process of breakdown in the system combines features of impurity and interband breakdown.