EVIDENCE FOR FIELD ENHANCED ELECTRON-CAPTURE BY EL2 CENTERS IN SEMIINSULATING GAAS AND THE EFFECT ON GAAS RADIATION DETECTORS

The performance of Schottky contact semiconductor radiation detectors fabricated from semi-insulating GaAs is highly sensitive to charged im purities and defects in the material. The observed behavior of semi-in sulating GaAs Schottky barrier alpha particle detectors does not match well with models that treat the semi-insulating material as either pe rfectly intrinsic or as material with deep donors (EL2) of constant ca pture cross section compensated with shallow acceptors. We propose an explanation for the discrepancy based on enhanced capture of electrons by EL2 centers at high electric fields and the resulting formation of a quasineutral region in the GaAs. Presented is a simple model includ ing field enhanced electron capture which shows good agreement with ex perimental alpha particle pulse height measurements.