OPTICAL EVALUATION OF THE IONIZED EL2 FRACTION IN PROTON (24 GEV) IRRADIATED SEMIINSULATING GAAS

Semi-insulating SI GaAs samples from a zone refined crystal were irrad iated with high energy protons (24 GeV/c, fluences up to 1.64x10(14) p /cm(2)). Optical spectra in transmittance and reflectance were accurat ely measured in the energy range of 0.6-1.4 eV to determine, through t he absorption coefficient, the concentrations of both neutral and ioni zed EL2 defects as a function of the proton fluence. Both these concen trations have been shown to increase linearly with the proton fluence; this behavior well explains the remarkable decrease of the charge col lection efficiency observed in proton irradiated GaAs detectors at dos es associated with high luminosity beams at a new particle collider ac celerator (e.g., the LHC at the CERN laboratory). (C) 1997 American In stitute of Physics.