Photocurrent mapping as a probe of transport properties and electric field distributions in cadmium zinc telluride detectors

We have performed two-dimensional cross-sectional photocurrent mapping of Cd_0.9Zn_0.1Te detectors grown by the high-pressure Bridgman method as a means of probing the electric field distribution. We have analyzed the results using a model based on the drift-diffusion equation. In the case of a uniform electric field and excitation far from the electrodes, the result is virtually identical in form to the Hecht relation. We adapt the Hecht relation to analyze photocurrent data and generalize it to the case of a nonuniform electric field. The spatial distribution of photocurrent for the material that we have examined suggests a nonuniformity in either the electric field or the electron mobility-lifetime product. These observations may help to explain the slope changes observed in detector response pulses