X-ray response of CdZnTe detectors grown by the vertical Bridgman technique: Energy, temperature and high flux effects

Amadé

Zanettini³

et al. 2020

Sci Rep

platinum is a promising candidate for the realization of blocking electrical contacts on cadmium-zinctelluride (cdZnte or cZt) radiation detectors. However, the poor mechanical adhesion of this metal often shortens the lifetime of the final device. In this work, a simple and effective procedure to obtain robust platinum contacts by electroless deposition is presented. Microscopical analysis revealed the final thickness and composition of the contact layer and its adhesion to the bulk crystal. The blocking nature of the Pt-CdZnTe junction, essential to obtain low noise devices, was confirmed by current-voltage measurements. the planar pt-cdZnte-pt detectors showed good room temperature spectroscopic performance with energy resolution of 4% (2.4 keV) and 3% (3.7 keV) FWHM at 59.5 and 122.1 keV, respectively. Finally, we showed, for the first time, that platinum contacts allow the estimation of the carrier lifetime and mobility of both holes and electrons by using current transient measurements. This demonstrated the optimal hole extraction capability of such contacts. CdTe and CdZnTe (CZT) have proven to be excellent materials for room temperature X-ray and gamma-ray detectors and they are gradually replacing other sensing systems in many applications. Electrical contacts on such detectors need to be customised according to the final purpose of the device and engineered depending on the properties of the starting material such as work function and bulk resistivity. A great interest has been addressed to platinum metal contacts 1-3 because Pt work function (~ 5.6 eV) leads to the formation of a high Pt-CZT Schottky barrier which limits the carrier injection and thus the leakage current. This is the reason why blocking contacts are usually adopted to realize high-resolution spectrometers 4. Electroless deposition technique is vastly used to deposit contacts on II/VI materials. The reason lies in its simplicity since no specific or expensive laboratory equipment is required. This method consists in the spontaneous reaction of the metal in salt form dissolved in a proper solvent with the detector material. The reaction takes place without the use of any external electric power and allows to realize chemically stable and reproducible contacts. Moreover, the oxide formation at the metal/semiconductor interface is minimised since contacts are realised immediately after the polishing step, hence reducing the air exposition of the highly reactive surface. This is crucial to reduce the effect of the oxide layer on the leakage current and charge collection efficiency. Lastly, fine tuning of electroless deposition parameters allows to control the final quality of the metallic layer in term of thickness and homogeneity. In this work, Pt contacts have been deposited by means of a electroless deposition technique based on alcoholic solution. The CdZnTe detectors have been realised and characterised thorough mechanical, structural, electrical, and spectroscopic analysis. This study is focused on explaining the role of the metal/se...

Section: Methodsmentioning

confidence: 99%

Improved electroless platinum contacts on CdZnTe X- and γ-rays detectors

Amadé

Zanettini³

et al. 2020

Sci Rep

“…In previously published articles using similar CdZnTe sensors [ 20 ] the values reported were in the range of the

. However, these values were obtained with planar sensor and therefore no small pixel effect.…”

Section: Results and Discussionmentioning

confidence: 86%

“…CdZnTe grown at IMEM-CNR (Parma, Italy) by Boron oxide encapsulated vertical Bridgman technique has already demonstrated optimal performance, both with a single-pixel contact geometry [ 20 ] and sub-millimeter pixel geometry (500 and 250

pitch) [ 21 ]. The excellent spectroscopic performance of this material and the absence of radiation-induced polarization effects up to fluxes of

photons

motivated the decision to test CdZnTe grown at IMEM-CNR for synchrotron application.…”

Section: Introductionmentioning

confidence: 99%

Fabrication of Small-Pixel CdZnTe Sensors and Characterization with X-rays

Tsigaridas

Zanettini²,

et al. 2021

Sensors

Over the past few years, sensors made from high-Z compound semiconductors have attracted quite some attention for use in applications which require the direct detection of X-rays in the energy range 30–100 keV. One of the candidate materials with promising properties is cadmium zinc telluride (CdZnTe). In the context of this article, we have developed pixelated sensors from CdZnTe crystals grown by Boron oxide encapsulated vertical Bridgman technique. We demonstrate the successful fabrication of CdZnTe pixel sensors with a fine pitch of 55 m and thickness of 1 mm and 2 mm. The sensors were bonded on Timepix readout chips to evaluate their response to X-rays provided by conventional sources. Despite the issues related to single-chip fabrication procedure, reasonable uniformity was achieved along with low leakage current values at room temperature. In addition, the sensors show stable performance over time at moderate incoming fluxes, below 106 photons mm−2s−1.

“…This attempt is fundamental in every field where the relevant information may be concealed or distorted by non-ideal behavior of the measuring instrument, such as the one of room temperature semiconductor detectors (RTSD). RTSDs are largely employed today for medical and astrophysical applications [ 1 ], as well as for environmental monitoring [ 2 ] and for high flux applications [ 3 , 4 ]. The main source of distortion is related to those events of radiation interaction for which the total energy deposited is inferior to the real energy of the incoming photon.…”

Section: Introductionmentioning

confidence: 99%

Gamma-Ray Spectral Unfolding of CdZnTe-Based Detectors Using a Genetic Algorithm

Amadé

Zambelli³

et al. 2020

Sensors

The analysis of γ-ray spectra can be an arduous task, especially in the case of room temperature semiconductor detectors, where several distortions and instrumental artifacts conceal the true spectral shape. We developed a genetic algorithm to perform the unfolding of γ-spectra in order to restore the true energy distribution of the incoming radiation. We successfully validated our approach on experimental spectra of four radionuclides (241Am, 57Co, 137Cs and 133Ba) acquired with two CdZnTe-based detectors with different contact geometries (single pixel and drift strip). The unfolded spectra consist of δ-like peaks in correspondence with the radiation emissions of each radioisotope.