Radiation detection using integrated GaAs HEMT electronics

A charge sensitive preamplifier (CSP) together with a shaper was integrated using the standard 0.3 mu m GaAs HEMT process of the "Fraunhofer-Institut für Angewandte Festkörperphysik" (IAF) on a 100 x 1000 mu m(exp 2) large chip area. The shaper has a filter time constant tau f = 10 ns to minimize the noise of the CSP, which was measured to be 450 rms electrons at an input capacitance CT = 1.55 pF. The circuit is operated with negative supply voltages of -3.5 and -4.5 V giving a total power dissipation of 20 mW. The overall amplification into 50 ohm is 18.8 mV/fC, corresponding to a 75 mV output signal for a charge of 25 000 electrons, which is the signal generated by 1 minimum ionizing particle (MIP) in a 200 mu m thick GaAs or 300 gm thick Si detector. To demonstrate the functionality of a fully GaAs based detection system the chip was wire-bonded to a GaAs pad detector and used at the T10 testbeam facility of the PS accelerator at CERN to record spectra of 5 GeV pions.