Photo-electronic investigation of CdZnTe spectral detectors

Using a focused and pulsed beam of 850-nm laser radiation, it is possible to assess a number of bulk properties of CdZnTe. The subbandgap pulsed radiation (pulse width 80 ns) excites a detectable signal from defects near the band edges in CdZnTe. This is detected using a conventional charge sensitive preamplifier. Further information is obtained by observing the transmitted optical beam simultaneously with the detected photo-induced current from the CdZnTe detector. The intensity of the laser beam is adjusted such that an average of 152 keV is deposited in the CdZnTe detector per optical pulse. Using optical polarizers, the electric field distribution has been measured without the space-charge-induced distortion of the electric field normally experienced when using higher intensity dc light sources. These results have been correlated with charge collection efficiency measurements. By varying the pulse repetition frequency (f_p), it may be possible to obtain information about the lifetime of shallow defects at room temperature.