CdZnTe semiconductor parallel strip Frisch grid radiation detectors

Abstract

CdZnTe wide band gap compound semiconducting material offers promise as a room temperature operated gamma ray spectrometer. Position-dependent free charge carrier losses during transport can prevent efficient charge carrier extraction from semiconductor detectors and severely reduce energy resolution. Hole trapping losses in CdZnTe radiation detectors are far worse than electron trapping losses and resolution degradation in CdZnTe detectors results primarily from severe hole trapping during transport. Coplanar radiation detectors improve energy resolution by sensing the induced charge primarily from the motion of electrons. Demonstrated is an alternative approach to single free charge carrier sensing, in which a parallel strip Frisch grid is fabricated on either side of a parallelepiped block. The detectors are three terminal devices, but require only one preamplifier for the output signal. The prototype devices demonstrate a considerable increase in energy resolution when operated in the true Frisch grid mode rather than the planar mode, with a demonstrated room temperature energy resolution for 662 keV gamma rays of 5.91% at FWHM for a 10"x 2mm x 10" device. Presently, high surface leakage currents prevent large voltages from being applied to the devices, which ultimately reduces their maximum achievable energy resolution. Further improvements are expected with the realization of reduced surface leakage currents.

Single-charge-carrier-type sensing with an insulated Frisch ring CdZnTe semiconductor radiation detector

“…Methods showing promise include "co-planar" and "small-pixeleffect" devices [1][2][3]. A simple method of achieving single-carrier performance was demonstrated with side contacts acting as the Frisch grid [4,5,7]. Unfortunately, all of the aforementioned designs suffer from problems, which include leakage current between the anode and grid, processing difficulties, or electric field distortions.…”

“…A signal is induced at the anode by the charge motion between the grid and the anode, whereas the Frisch grid screens out the induced signal from slow moving positive ions drifting towards the cathode. Placing the grid near the anode ensures that the origin of induced signal is from those electrons that drifted from the detector volume into the measurement region, thereby causing the signal to form mainly from electron motion.Several methods of creating a Frisch grid effect without an embedded grid have been studied in semiconductor detectors [1][2][3][4][5]. Methods showing promise include "co-planar" and "small-pixeleffect" devices [1][2][3].…”

“…Several methods of creating a Frisch grid effect without an embedded grid have been studied in semiconductor detectors [1][2][3][4][5]. Methods showing promise include "co-planar" and "small-pixeleffect" devices [1][2][3].…”

“…Single charge carrier device designs alleviate many of the problems caused by hole trapping. Such 'electron-only' devices rely mostly on the transport of electrons to induce a signal and, by negating the deleterious effects of hole trapping, give improved energy resolution.Frisch-grid-based designs have become a popular choice for semiconductor single carrier radiation detectors [1][2][3][4][5]. The Frisch grid is a conductive screen structure originally fashioned for gas-filled ion chambers and is usually located near the anode [6].…”

“…Frisch-grid-based designs have become a popular choice for semiconductor single carrier radiation detectors [1][2][3][4][5]. The Frisch grid is a conductive screen structure originally fashioned for gas-filled ion chambers and is usually located near the anode [6].…”