Two-dimensional position sensing Si detectors: Current and charge pulse characteristics

The current and charge pulse characteristics of two-dimensional position sensing Si detectors (PSDs) employing resistive charge division have been measured by making use of pulsed photon systems. The detectors studied are discrete two-dimensional PSDs where individual gold and orthogonal aluminium strips are deposited on the front and back surfaces, respectively, of the silicon wafer. Resistive charge division is accomplished by two external resistor networks. Detector fabrication and the pulsed photon systems are described. The anomalous currents (i.e., polarity reversal with time) exhibited by these detectors, which we reported earlier, have been studied and their time characteristics determined. Calculations based on a simplified model of the detector predict these anomalous currents, and the results of the calculations are compared with measurements. The currents characteristic of two-dimensional detectors have measured time durations considerably longer than those measured for equivalent one-dimensional detectors. Further, the anomalous currents result in ballistic deficits which are greater than unity, an effect entirely absent for one-dimensional detectors. For detectors having fixed area and thickness, the requirement that these detectors exhibit near distortion-free position response for heavy ions in the presence of intense background fluxed (i.e., protons) imposes strong restrictions on the total resistance of the external resistor networks, which are discussed. (orig.)