Characterisation of low pressure VPE GaAs diodes before and after 24 GeV/c proton irradiation

Abstract

GaAs Schottky diode detectors have been fabricated upon Low Pressure Vapour Phase Epitaxial GaAs. The devices were characterised before and after a $1.25 \times 10^{14}$~cm$^{-2}$ 24GeV/c proton fluence. The as fabricated Ti-GaAs barrier height was measured, via two electrical methods, to be $0.81\pm0.005$ and $0.85\pm0.01$~eV and a space charge density of $2.8 \pm 0.2 \times 10^{14}$~cm$^{-3}$ was determined. The current was greater than that expected for an ideal barrier with the excess attributed to generation current from the bulk. The charge collection efficiency, determined from front alpha illumination and 60 keV gamma irradiation, was inexcess of 95% at 50V reverse bias. After irradiation the reverse current, measured for a bias of 200V at 20$^{o}$~C, increased from 90~nA to 1500~nA due to radiation induced generation centres. Deep levels were showed to be present using capacitance techniques. The charge collection of the device determined from front alpha illumination fell to $32\pm5$% at a reverse bias of 200V.