Analysis of edge and surface TCTs for irradiated 3D silicon strip detectors

Abstract

We performed edge and surface Transient Current Technique (TCT) measurements of short, double sided 3D silicon strip detectors. Double sided 3D devices are a useful counterpart to traditional planar devices for use in the highest radiation environments. The TCT technique allows the electric field in the 3D devices to be probed in a way not possible before. The TCT technique uses the current waveform produced by the detector in response to a near delta function point laser pulse (illumination). The waveforms are recorded as a function of illumination position over the surface of the device under test as a function of detector bias.This data gives information on the portion of the induced signal from electron or hole motion. From the rise times of the signals the velocity profile of the carriers in the devices and therefore electric fields can be determined. The collected charge was calculated from the integral of the waveforms.The detectors were tested prior to irradiation, after irradiating to a dose of 5 × 1015 1 MeV equivalent neutrons/cm2, and after periods of annealing at elevated temperatures. Annealing was achieved in situ by warming to 60°C for 20 to 600 minutes corresponding to room temperature annealing of between 8 and 200 days.While before irradiation, full lateral depletion between the columns occurs at low bias voltages, at approximately 3 V, a uniform carrier velocity between the columns is not achieved until 40 V. Both the drift of electrons and holes provide equal contributions to the measured signals. After irradiation there is clear charge multiplication enhancement along the line between columns with a very non-uniform velocity profile in the unit cell of the device. In addition, charge trapping greatly suppresses the contribution of the holes on the signal produced.