Sensitivity of PCDs to protons and photons as a function of applied detector voltage

The authors describe the results of measurements taken at the Los Alamos National Laboratory to determine how photoconductive detector (PCD) sensitivity changes with applied field strength. The PCDs were of two types: iron-doped indium phosphide (InP:Fe) and neutron-damaged gallium arsenide (GaAs:ND). The PCDs were fabricated with a 1-mm gap across their electrodes. The voltage across the electrodes was varied from -900 V to +900 V for this study. Proton sensitivity was measured using bunched protons. The magnitude and duration of each bunch were monitored by a nonintercepting beam monitor. The incident energy of the protons was varied from 4 to 11 MeV. Ten-pulse averages were taken at each setting; the charge measured from the PCD was normalized to the signal recorded by the beam monitor. Sensitivity to photons was measured using an 826-nm laser and electronics that recorded the peak signal from the PCD. The proton and photon data for the GaAs detectors have the same general trend, but are qualitatively different for the InP:Fe detectors.<>