Hopping-Type Electronic Processes in Pre-Breakdown Electrical Fields in Insulators with Defect Centers

Field-induced electronic jumps over the system of impurity centers in ionic insulators in pre-breakdown electric fields are discussed. An alkali halide crystal with electrically neutral F-color centers and negatively charged F'-centers is used as a model system. The Radiative Tunnel Transitions (RTT) of an outer electrons of F'-centers over the network of F-sites under the action of an applied electric field, could provide a specific contribution to the total electronic conductivity. This mechanism has similarities with activationless hopping conductivity in strong electric fields in compensated semiconductors. The processes of inter-electronic energy transfer could provide yet another contributing factor towards the enhancement of the pre-breakdown electronic conductivity.