Behaviour of high purity semiconductor surface-barrier nuclear radiation detectors at low temperatures.

The characteristics of a germanium and a silicon surface barrier detector have been examined at low temperatures (78 to 5 K). Preliminary results have also been obtained from a gallium arsenide detector. All detectors were fabricated from high purity material. Below some critical temperature (10 K in germanium and 32 K in silicon) the spectral response to y-rays deteriorated markedly, particularly for low bias. Near liquid helium temperature best resolutions of 10.0 keV at 662 keV and 3.0 keV at 122 keV were obtained with the germanium and silicon detectors respectively. Relative efficiency measurements found no change in the sensitive depth with temperature in contrast to the indications of the capacitance. A model based on field-assisted detrapping is proposed to account for the fact that sensitive depth is independent of temperature. The behaviour of the capacitance and the existence of slow components in the pulse risetime are explained in terms of the equivalent circuit of the detector. The energy resolution of the gallium arsenide detector did not change on cooling to 7 K where a resolution of 3.9 keV at 60 keV was measured