Characterisation of Redlen high-flux CdZnTe

Abstract

CdZnTe is a promising material for the current generation of free electron laser light sources and future laser-driven γ-ray sources which require detectors capable of high flux imaging at X-ray and γ-ray energies (> 10 keV). However, at high fluxes CdZnTe has been shown to polarise due to hole trapping, leading to poor performance. Novel Redlen CdZnTe material with improved hole transport properties has been designed for high flux applications. Small pixel CdZnTe detectors were fabricated by Redlen Technologies and flip-chip bonded to PIXIE ASICs. An XIA Digital Gamma Finder PIXIE-16 system was used to digitise each of the nine analogue signals with a timing resolution of 10 ns. Pulse shape analysis was used to extract the rise times and amplitude of signals. These were measured as a function of applied bias voltage and used to calculate the mobility (µ) and mobility-lifetime (µτ) of electrons and holes in the material for three identical detectors. The measured values of the transport properties of electrons in the high-flux-capable material was lower than previously reported for Redlen CdZnTe material (µ e τ e ∼ 1 × 10 −3 cm 2 V −1 and µ e ∼ 1000 cm 2 V −1 s −1 ) while the hole transport properties were found to have improved (µ h τ h ∼ 3 × 10 −4 cm 2 V −1 and µ h ∼ 100 cm 2 V −1 s −1 ).

Effect of Deep-Level Defects on the Performance of CdZnTe Photon Counting Detectors

“…Based on the above analysis, we imply that CdZnTe detectors with a good counting performance have lower In , [In V ] and Te concentrations and a higher Te concentration. The above results agree well with [11], that the high-flux CdZnTe detectors have a higher hole mobility-lifetime product and lower electron mobility-lifetime product.…”

“…These large-volume, good-uniformity CdZnTe photon counting detectors, which can detect a photon flux in the order of a hundred million mm −2 s −1 , are necessary for many applications such as medical and industrial imaging [8,9]. Although such high-flux CdZnTe detectors have been reported [10], it is still a challenge to achieve large-scale commercial applications, primarily due to the material defects which can lead to the polarization effect [11][12][13][14][15][16]. Under high X-ray flux conditions, excessive positive space charges formed by trapped holes build up inside the detector, which have an opposite effect on the externally applied voltage and ultimately result in a non-uniform electric field and catastrophic device failure.…”

Resolution characterization of a silicon-based, photon-counting computed tomography prototype capable of patient scanning

“…Furthermore, the charge carrier mobility is high for both electrons and holes, minimizing the risk of polarization and preventing energy blur due to slow charge collection. This makes it possible to combine high count-rate capability with high energy resolution, and energy resolutions in the range of 3.5 to 5.4 keV full-width at half-maximum (FWHM) or 1.6 to 2.3 keV root mean square (RMS) has been reported for a silicon strip detector for CT. 23,24 Even though CdTe sensors can achieve resolutions below 1 keV when connected to slower readout electronics, 20,25,26 typical energy resolution values reported for high-flux CdTe detectors are 6 to 10 keV FWHM (2.5 to 4.2 keV RMS). 27,28 For dose efficiency reasons, the depth of a photon-counting detector is determined by its material.…”

Overview of GaAs und CdTe Pixel Detectors Using Medipix Electronics

“…The applications require photon fluxes larger than 10 8 photons s −1 and mm −2 . This requires further improvement of the material and the contact technology, for example, presented by Prokesch et al [29] and Thomas et al [30]…”