Beam test measurements on GaAs strip and pixel detectors

Abstract GaAs strip and pixel detectors constructed in Aachen have been tested in a 1.4 GeV electron beam in Bonn and in a 5 GeV electron beam at DESY in February and May 1997. The strip detectors had a pitch of 50μm with a strip width of 25μm and were made of a 250μm thick Freiberger SI-GaAs wafer. The strip detectors included a punch-through bias structure and an integrated coupling capacitor. Additionally, an improved backside contact was formed, allowing a safe operation of the detector in a soft breakdown regime. Using the fast PreMux 128 preamplifier multiplexer chip ( τ p = 50 ns) a signal-to-noise ratio of 13 was obtained at normal beam incidence for a bias voltage of 200 V, leading to a spatial resolution of 11 μm with a simple COG algorithm. The 8 × 16 pixel array with a pixel size of 125 × 125 μ m 2 was read out with the PreMux128 as well. With a double-metal technique, it was possible to bond the single-pixels linearly to the amplifier chip. The obtained signal-to-noise ratio of 30 in combination with a COG algorithm lead to the digital resolution value of 36 μm for both pixel coordinates.