THEORY OF INJECTED CURRENT BEHAVIOR ASSOCIATED WITH BLOCKED IMPURITY-BAND-CONDUCTION

A theoretical investigation has been made of the space charge distribution and its effect on injected electron current behavior in blocked impurity-band-conduction (IBC) photodetectors. The design considered is one commonly used for long wavelength infrared (LWIR) detectors. In this configuration, there is a blocking layer where IBC does not occur, and this results in diminished dark current. The operating temperatures considered are around 10 K, so that the thermal voltage is much smaller than the applied biases of interest here, with the consequence that carrier diffusion can be neglected. In addition, thermally or optically generated carriers as well as carrier recombination are not taken into account. This investigation is thus concerned only with injected dark current. Furthermore, it is assumed that the contacts are ohmic. It is felt that an understanding of space charge fields and dark current injection is essential to understanding the behavior of IBC devices as LWIR detectors. Calculated results include electric field and electrostatic potential vs position, and injected current vs bias. It is shown that space charge fields cause asymmetry in the current vs bias behavior for positive as compared with negative applied biases. © 1990.