Radiation studies for GaAs in the ATLAS inner detector

Abstract

We estimate the hardness factors and the equivalent 1 MeV neutron fluences for hadrons fluences expected at the GaAs positions wheels in the ATLAS Inner Detector. On this basis the degradation of the GaAs particle detectors made from different substrates as a function of years LHC operation is predicted.

Radiation-induced damage in GaAs particle detectors

“…The energy of the neutrons is the typical energy expected for the background neutron flux at the LHC. Fig [3] Electron and hole contributions to the charge signal after 2x10 14 p cm -2 measured using alphas on the front and back of the device.…”

“…Fig[4] shows the correlation between cce for 200 µm thick detectors measured at 200 V and the calculated NIEL [2,3] for the various particles used in this study. The damage attributed to each particle type has been weighted by its relative NIEL and the calculated energy loss is well correlated with the observed damage.…”

“…The radiation induced defects in the crystal may be reduced by thermal annealing. Arsenic anti-site defects introduced by irradiation have been shown to anneal at temperatures above 450°C [3]. Detectors were thermally annealed at 450°C in a rapid thermal annealer after exposure to 1 x 10 14 p cm -2 .…”

Analysis of uniformity of as prepared and irradiated SI GaAs radiation detectors

“…To investigate their effect on the detection parameters, like the mean free drift lengths of the electrons, Le, and holes, hh, the cce expressions obtained by applying the simple Hecht model to a fully active detector for the detection of pand a-particles as well as of X-rays, can be used. The model, which considers the charge trapping and no detrapping and recombination processes during the drift of the charge carriers towards their electrodes of collection [19], predicts, when the electrons and holes are collected with the same efficiency (that is he=hh), that ccep=cce,=cc% independently from the exposure side [20].…”

“…No data of tp are available for GaAs. Likely in GaAs tp at 300 K and 10 kV/cm is of the order of lo-' s [24], and is comparable to or lower than the charge carrier lifetime in unirradiated GaAs [8,16,20].…”