Single-polarity charge sensing in ionization detectors using coplanar electrodes

Abstract

A new method to preferentially sense the collection of single-polarity charge carriers in ionization detectors is presented. It uses coplanar electrodes to closely emulate the function of Frisch grids commonly employed in gas and liquid ionization detectors. The coplanar electrode structure allows for easy implementation on semiconductor detectors. This method can be used to obtain good energy resolution from detectors in which only one polarity type of carriers is efficiently collected. Experimental results using a CdZnTe detector demonstrate the effectiveness of this method.

Electron trapping nonuniformity in high-pressure-Bridgman-grown CdZnTe

“…The potential of CdZnTe has been demonstrated through many material and detector technology developments over the last decade. [1][2][3][4][5][6][7][8][9][10][11][12][13] The material has the desirable intrinsic properties of a wide bandgap necessary for room-temperature operation and a high average atomic number for efficient gamma-ray stopping. Furthermore, the CdZnTe material that is commercially available today exhibits negligible polarization effects, has a high bulk resistivity, and has reasonably good electron collection properties.…”

Measurements on the spectroscopic performance of CdZnTe coplanar grid detectors

“…The first major stride in single-polarity charge sensing of room temperature semiconductor detectors was made by Luke (1994), who developed an electrode structure called the coplanar grid, based on the collection of the charge carriers (electrons only). Utilization of the coplanar grid electrode structure in a device reduces tailing in the CZT crystal caused by the charge trapping.…”

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

“…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].…”

“…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].…”

“…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].…”