Irradiation of optically activated SI-GaAs high-voltage switches with low and high energy protons

Semi-Insulating Gallium Arsenide (SI-GaAs) devices have been tested for rad iation hardness with 3-4 MeV or 24 GeV proton beams. These devices can be o perated in de mode as optically activated electrical switches up to 1 kV. B oth single switches (vertical Schottky diodes) and multiple (8) switches (p lanar devices) have been studied, by analyzing their current-voltage (I-V) reverse characteristics in the dark and under red light illumination, both before and after irradiation. We propose to use them in the system of high-voltage (-600 V) switches for the microstrip gas chambers for the CMS experiment at CERN. Low energy protons (3-4 MeV) were used in order to produce a surface damage below the Schottky contact: their fluence (up to 2.6x10(15)) p/cm(2)) give s a high-dose irradiation. The high energy proton irradiation (energy: 24 G eV, fluence: 1.1x10(14) p/cm(2)) reproduced a ten years long proton exposur e of the devices in CMS experiment conditions. For low energy irradiation, limited changes of the I-V curves in the dark h ave been observed, with at most a fourfold increase of the leakage current: after exposure, however, the breakdown voltage decreases significantly. For high energy irradiation, we observed - for the vertical Schottky diodes biased at -600 V - an increase of the leakage current and a reduction of t he photocurrent after irradiation, with respect to pre-irradiation conditio ns. For these diodes, the reduction of the photocurrent/dark current ratio was 25:1. At the same proton energy, an analogous behaviour was shown by th e planar devices, but after irradiation the current gain may reduce over th ree orders of magnitude.