Study of contacts to CdZnTe radiation detectors

Abstract

This study characterizes, for the first time, contacts to CdZnTe radiation detectors by measuring the dark noise spectra as a function of the applied bias. The noise currents are correlated with the dc dark current-voltage characteristics of CdZnTe x-ray and gamma-ray detectors. In order to identify and separate the role of the contacts in the overall performance, the measured noise phenomena is correlated with detector configuration and contact design as well as the growth method of the CdZnTe crystals, contact technology, and passivation. Several contact technologies (electroless gold, and a number of evaporated metallic contacts including gold, indium, zinc, titanium, aluminum, and platinum contacts) are compared. Contacts to CdZnTe crystals grown by high pressure Bridgman are compared with contacts to CdZnTe crystals grown by modified Bridgman. Contacts of resistive detectors as well as of Schottky detectors are reported. Large area symmetric contacts are compared with small area pixelized contacts. The role of the metallization used for contacts, the role of surface effects and passivation, and the role of contact design are discussed.

Characterization of dark noise in CdZnTe spectrometers

“…We have recently applied noise measurements to optimize detector technology and improve spectral performance. 4 The effect of dark noise on energy resolution of CdZnTe spectrometers is reported in Ref. 5.…”

Dark noise currents and energy resolution of CdZnTe spectrometers

“…Charaterization of dark noise in CdZnTe spectrometers and systematic noise measurements of CdZnTe detectors are reported elsewhere. 3,9 At present, the performance of CdZnTe spectrometers is considered to be mainly limited by incomplete charge collection 14 and the fluctuations in the collected charge (expressed by the standard deviation which is the square root of the variance of the collected charge). 15 The calculated standard deviation of the collected charge for a high quality CdZnTe spectrometer modeled with τ e = τ p = 2 µs, µ e = 1000 cm 2 /v · s and µ p = 100 cm 2 /v · s (i.e., µ e · τ e = 2 × 10 -3 cm 2 /v and µ p · τ p = 2 × 10 -4 cm 2 /v is, approximately, 4 keV for 81 keV photons (Ba 133 ).…”

“…The latter includes detector configuration, contacts technology (contact material and deposition technique), and surface properties (passivation) as well as the bulk material properties that are determined by the CdZnTe crystal growth method. [1][2][3][4] The more common spectrometer configuration is currently the metal-semiconductor-metal (MSM) detector type while the configuration with the potential for lowest leakage dark current is the p-i-n diode. 5,6 We have recently characterized the dark noise currents of CdZnTe spectrometers with the MSM configuration which are fabricated in CdZnTe (Zn = 10%) crystals grown by high pressure Bridgman 7 as well as modified Bridgmam.…”

“…8 It has been observed that non-injecting contacts (provided by evaporated gold contacts) and proper surface passivation are necessary to reduce the dc value of the dark current. 3,4 To obtain the dark current limited by the bulk material, a three-terminal device has been found to be essential. 4 The leakage current degrades the energy resolution of the detector.…”

“…The measured noise power spectral density of these noise mechanisms correlated with the technology of CdZnTe spectrometers, is reported elsewhere. 3,9 In this paper, we analyze quantitatively the effect of the dark noise currents upon the energy resolution. We report direct measurements of peak broadening (Received October 21, 1997; accepted December 12, 1997) Dark Noise Currents and Energy Resolution of CdZnTe Spectrometers due to the dark noise.…”