BEAM TEST MEASUREMENTS ON GAAS STRIP AND PIXEL DETECTORS

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 DES Y in February and May 1997. The strip detectors had a pitch of 50 mu m with a strip width of 25 mu m and were made of a 250 mu m thick Freib erger SI-GaAs wafer. The strip detectors included a punch-through bias structure and an integrated coupling capacitor. Additionally, an impr oved backside contact was formed, allowing a safe operation of the det ector in a soft breakdown regime. Using the fast PreMux128 preamplifie r multiplexer chip (tau(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 mu m with a simple COG algorithm. The 8 x 16 pixel array with a pixel size of 125 x 125 mu m(2) was read out with the PreMux128 as well. With a double-metal technique, it was poss ible to bond the single-pixels linearly to the amplifier chip. The obt ained signal-to-noise ratio of 30 in combination with a COG algorithm lead to the digital resolution value of 36 mu m for both pixel coordin ates. (C) 1998 Elsevier Science B.V. All rights reserved.