CHARACTERIZATION OF LOW-PRESSURE VPE GAAS DIODES BEFORE AND AFTER 24 GEV C PROTON IRRADIATION/

GaAs Schottky diode particle detectors have been fabricated upon low-p ressure vapour-phase epitaxial GaAs. The devices were characterised wi th both electrical and charge collection techniques. The height of the Ti-GaAs barrier used was determined via two electrical methods to be( 0.81 +/- 0.005) and(0.85 +/- 0.01)eV. The current density was greater than that expected for an ideal Schottky barrier and the excess curren t was attributed to generation current in the bulk of the material. A space charge density of (2.8 +/- 0.2)x 10(14)cm(-3) was determined fro m capacitance voltage characterisation. The charge collection efficien cy was determined from front alpha illumination and 60 keV gamma irrad iation to be greater than 95% at a reverse bias of 50 V. The diodes we re characterised after an exposure to a radiation fluence of 1.25 x 10 (14) 24 GeV/c protons cm(-2). The reverse current measured at 20 degre es C increased from 90 to 1500 nA at an applied reverse bias of 200 V due to the radiation induced creation of extra generation centres. The capacitance measurements showed a dependence upon the test signal fre quency which is a characteristic of deep levels. The capacitance measu red at 5 V reverse bias with a test frequency of 100 Hz fell with radi ation from 300 to 40 pF due to the removal of measurable free carriers . The charge collection of the device determined from front alpha illu mination also fell to (32 +/- 5)% at a reverse bias of 200 V. (C) 1998 Elsevier Science B.V. All rights reserved.