Thermal cycling of InGaP radiation detectors for a CubeSat mission

Abstract

Two Indium Gallium Phosphide (In_0.5Ga_0.5P, InGaP) semiconductor radiation detectors (p⁺-i-n⁺ photodiodes, one 110 μm diameter and one 400 μm diameter) intended to be used on a CubeSat mission to explore the radiation environment in low earth orbit have been thermally cycled between −50 °C and +150 °C a total of 663 times. The performance of the devices was investigated as a function of number of temperature cycles. It was demonstrated that the detectors, their wirebonds, and their packaging survived the cycling with their performance intact. At the end of the thermal cycling the devices’ i layers remained fully depleted (at reverse bias, V_R, = 10 V), leakage currents were reduced, and the energy resolutions of the 110 μm and the 400 μm device improved from 910 eV ± 20 eV and 1320 eV ± 40 eV to870 eV ± 20 eV and 1210 eV ± 40 eV, respectively. This suggested that degradation of the detectors due to thermal cycling in orbit is unlikely to occur over a nominal 31 day mission in which approximately 500 thermal cycles may be expected. The work did not examine the effects of vacuum or radiation damage on the detectors.