SI-GaAs detectors with epitaxial junction

High leakage currents and incomplete charge collection limit the performanc e of detectors obtained from bulk semiinsulating (SI) GaAs. In this contest , a crucial role is played by the electron limiting contact. We have invest igated the effect of an epitaxial p-type layer deposited on the semi-insula ting substrate in place of the usual Schottky contact. Electrical character ization evidences an effect of the p-layer only at low voltages, but radiat ion detection experiments show an improvement of the charge collection effi ciency, which is function of the doping level of the p-layer. In particular both a and x irradiations give evidence of gain mechanisms in the collecte d charge. From these results, the strong relation between the structure of the electron-blocking interface and the charge collection properties of the se detectors comes out.