A study of the signal rising edge produced by a charge sensitive preamplifier connected to a 4H-SiC detector

Abstract

In a general semiconductor detector system, the output amplitude of the charge-sensitive preamplifier (CSA) is proportional to the total charge induced by incident particles. The rising edge of the output signal provides information on the input current. The shape of the rising edge is not only affected by the carrier drifting but the discharge process of the equivalent capacitance (the detector capacitance and the capacitance caused by the detector package and the connecting cable, namely the stray capacitance) and the input resistance of the CSA. The equivalent capacitance and the input resistance often has a time constant of tens nanoseconds, which significantly affects the rising edge, particularly for fast detectors such as silicon carbide or diamond. This paper describes an α-particle testing system based on a Schottky 4H-SiC detector. The junction capacitance of the detector can be adjusted by changing the bias voltage, and the derivative waveforms of the CSA output are analyzed using an equivalent circuit. The results show that the falling edge of the derivative waveform corresponds to the discharge process of the equivalent capacitance and the input resistance in the circuit. The parameters of the detector capacitance, the stray capacitance and the input resistance can be obtained through fitting the decay time. The duration of the induced current of the detector can be measured from the rising edge of the derivative waveform. By comparing the theoretical and the measured value, the carrier mobility at different bias voltages can be derived.