CHARACTERIZATION OF DARK NOISE IN CDZNTE SPECTROMETERS

Systematic measurements of dark noise spectra of CdZnTe x- and gamma-r ay spectrometers, correlated with the de I-V characteristics and detec tor technology, are reported. The dark noise of two innovative CdZnTe spectrometer configurations are studied: metal-semiconductor-metal (MS M) resistive detectors with three terminals as well as heterostructure PIN detectors with thermally evaporated n(+) CdS and p(+) ZnTe contac ts, which are fabricated on high pressure Bridgman CdZnTe (Zn = 10%) c rystals. The two innovative CdZnTe spectrometer configurations present ed here exhibit very low dark (leakage) current. By reducing the de va lue of the dark (leakage) current below 1 nA, shot noise becomes the d ominant noise mechanism and the contribution of 1/f noise becomes negl igible. The use of non-injecting contacts (evaporated gold) for the MS M detectors and the operation of the PIN detector in the reverse bias mode prevent generation-recombination noise which becomes dominant wit h injecting contacts (for example MSM detectors with evaporated indium and titanium contacts) or when operating the PIN detector in the forw ard bias mode. Surface leakage is reduced by applying surface passivat ion but is eliminated only by using the three terminal MSM configurati on which exhibits simple shot noise instead of the suppressed shot noi se observed in the two terminal MSM spectrometers. The noise measureme nts are useful for optimizing detector technology.