THE DEPLETION PROPERTIES OF SILICON MICROSTRIP DETECTORS WITH VARIABLE STRIP PITCH

We have investigated the depletion properties of trapezoidal shaped silicon microstrip detectors which have variable strip pitch [1]. Four types of detectors were examined: three detectors have constant strip width and a fourth has a varying strip width. The detectors are single sided with readout performed via p+ strips. The depletion properties of the devices were measured using two different methods. The first used capacitance versus voltage measurements, while the second used a 1060 nm wavelength laser coupled to a single mode fiber with a mode field diameter less than 10 mum. The small laser spot size allowed for the depletion depth to be measured in a localized area of the detector. The laser induced charge on an electrode was measured as a function of reverse bias voltage using a sensitive charge preamplifier. The depletion voltages of the detectors demonstrate a strong dependence upon the ratio of strip width to strip pitch. Moreover, these measurements show that a large value of this ratio yields a lower depletion voltage and vice versa.