It is shown that measurement of thermal activation energies for both Ohmic and space-charge-limited conduction over a broad temperature range enables the deduction of both depth and concentration of localized levels in a semi-insulator, while measurement of the activation energy for Ohmic conduction alone is rarely definitive for a wide band-gap material. The basis for interpreting thermal activation energies for electrical conduction is discussed in detail. The analysis is applied to recent results on HgS, GaP, CdS, and ZnS: Cd.

• Received 11 July 1968

DOI:https://doi.org/10.1103/PhysRev.180.785