Measurements on GaAs strip and pixel detectors in a 50 GeV pion beam

GaAs strip and pixel detectors constructed in Aachen have been tested at CERN in a 50 GeV pion beam in September 1995 in collaboration with the CMS Tracker group. The strip detectors had a pitch of 100 μm and were made of a 250 μm thick Freiberger SI-GaAs wafer. The three strip detectors had a strip width of 25, 50 and 75 μm, respectively. Using the fast PreMux128 preamplifier multiplexer chip (τp=50 ns) a signal to noise ratio of 15 was obtained for the widest strips at normal beam incidence for a bias voltage of 170 V. The 8 x 8 pixel arrays with a pixel size of 1 x 1 mm2 and 0.5 x 0.5 mm2, respectively, were read out with the PreMux128 as well. Here a signal of 12500e- was obtained for both detectors, leading to a maximum signal to noise ratio of 20 at perpendicular beam incidence and 170 V bias voltage. (orig.)