The operation near liquid helium temperature of a gold-barrier hyper-pure germanium detector for gamma-rays

Abstract

Diode characteristics and spectral response to 137Cs γ-rays of a gold-barrier detector made from hyper-pure germanium (net donor concentration 3 x 10 11cm-3) were examined over the temperature range 5 -78°K. Trapping at the primary shallow donor is believed responsible for poor energy resolution at low temperatures. At 5°K a best resolution of 10 keV FWHM was obtained. Efficiency measurements indicate no change in depletion depth on cooling to 5°K with constant bias, in contrast to capacitance measurements. The latter variation, however, can be explained in terms of the response of the detector equivalent circuit to bridge frequency and carrier freeze-out effects. Field-assisted de-trapping at the primary shallow donors is believed responsible for the temperature independent depletion depth and an improvement in resolution with bias in the low temperature carrier freeze-out region (< 10°K).