Polarization Phenomena in CdTe Nuclear Radiation Detectors

Nuclear radiation detectors made from high resistivity chlorine doped cadmium telluride grown by the travelling heater method were evaluated. Short term performance for ¿, ß, and ¿ radiations was good but the long term performance (>1 min) was degraded by a decrease in the full energy pulse height and ¿-ray efficiency with time after the bias voltage was applied. A model which considers the effects of deep acceptors which slowly ionize (~103 s) to an equilibrium concentration ~5 × 1011/cm3 can explain the experimental findings on the changes of pulse shape, pulse amplitude, capacitance, energy resolution, and ¿-ray efficiency with time. The operating conditions required for satisfactory stability in these detectors may be inconvenient to the user.