RESPONSE CHARACTERISTICS OF EXTRINSIC PHOTOCONDUCTORS

The speed of response of extrinsic germanium photoconductors is limited by the dielectric relaxation response time τρ= εε0ρ, when the resistivity of the photoconductor rises to the MΩ·cm or higher resistivity range. Further, dielectric relaxation components appear only when the drift length of charge carriers is comparable to or greater than the interelectrode distance. The appearance of the dielectric relaxation response-time component arises when a significant fraction of the photogenerated charge carriers is swept out of the photoconductor before recombination leaving a space charge throughout the crystal. For mercury-and copper-doped germanium photoconductors which were studied, an enhanced photosensitivity is observed with increasing bias. For low backgrounds, or high-resistivity conditions, the effect is largest and appears to correlate with the onset of the dielectric relaxation effects. © 1969 The American Institute of Physics.