Investigation of the spectral improvement of a capacitive Frisch-grid CdZnTe detector by using infrared stimulation

A capacitive Frisch-grid CdZnTe detector with different lengths of the Frisch rings has been fabricated, and the influence of infrared (IR) stimulation on the spectral performance of the detector has been investigated. IR stimulation at a wavelength (940 nm), close to the absorption edge of the CdZnTe, was found to improve the detector's spectral performance significantly. IR radiation was noted to influence the detector's sensitivity, changing the equilibrium between free and trapped carriers and improving the charge collection. The degree of improvement was different for detectors with different lengths of the Frisch rings and depended on the weighting potential distribution and the IR illumination intensity. For example, improvement was obtained in the energy resolution (FWHM) at 662 keV from 3.3% without illumination to 2.3% with a low intensity (120 mu W) of IR illumination for the capacitive Frisch-grid CdZnTe detector with an 8-mm-long Frisch ring. Good energy resolution could be obtained even at low operating voltages.