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Room Temperature Semiconductor Detectors: Development and Applications

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A special issue of Sensors (ISSN 1424-8220). This special issue belongs to the section "Physical Sensors".

Deadline for manuscript submissions: closed (31 March 2021) | Viewed by 37759

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Special Issue Editors

Dr. Leonardo Abbene

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Guest Editor

Department of Physics and Chemistry, University of Palermo, Viale delle Scienze, Edificio 18, 90128 Palermo, Italy
Interests: X-ray and gamma-ray detectors; CdTe and CdZnTe detectors; digital pulse processing electronics; medical applications; astrophysical applications
Special Issues, Collections and Topics in MDPI journals

Dr. Matthew Charles Veale

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Guest Editor

Rutherford Appleton Laboratory, UKRI Science & Technology Facilities Council, Oxfordshire, UK
Interests: Compound Semiconductors; X-Ray Imaging;X-Ray Spectroscopy; MHz Imaging

Dr. Andrea Zappettini

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Guest Editor

IMEM-CNR,Istituto Materiali per l’Elettronica e il Magnetismo, Consiglio Nazionale delle Ricerche Parco Area delle Scienze 37/A 43124 Parma, Italy
Interests: development of x and gamma ray detectors based on CzZnTe: crystal growth, material characterization, device processing, detector characterization

Special Issue Information

Dear Colleagues,

Over the last two decades, room-temperature semiconductor detectors (RTSDs) have been extensively proposed for X-ray and gamma-ray spectroscopy and imaging, opening new perspectives in several application areas such as synchrotron science, homeland security, medical imaging, and astrophysics. RTSDs are an important class of X-ray and gamma-ray sensors able to perform high-resolution spectroscopy near room-temperature conditions. Several high-Z and wide-bandgap compound semiconductors (CdTe, CdZnTe, GaAs, HgI₂, TlBr) have been developed, and continuous efforts have been made in the advancement of the crystal growth and device fabrication technologies.

In this framework, we are glad to edit this Special Issue on “Room Temperature Semiconductor Detectors: Development and Applications".

This Special Issue aims to receive submissions of both review and original research articles related to the state-of-the-art in RTSD sensors as well as prospects for future developments and applications.

Dr. Leonardo Abbene
Dr. Matthew Charles Veale
Dr. Andrea Zappettini
Guest Editors

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Sensors is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

compound semiconductor detectors
X-ray and gamma-ray detectors
CdZnTe detectors
CdTe detectors
GaAs detectors
HgI2 detectors
TlBr detectors
SiC detectors
energy-resolved X-ray imaging
medical imaging

Published Papers (13 papers)

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13 pages, 2658 KiB

Open AccessArticle

Energy Recovery of Multiple Charge Sharing Events in Room Temperature Semiconductor Pixel Detectors

by Antonino Buttacavoli, Gaetano Gerardi, Fabio Principato, Marcello Mirabello, Donato Cascio, Giuseppe Raso, Manuele Bettelli, Andrea Zappettini, Paul Seller, Matthew C. Veale and Leonardo Abbene

Sensors 2021, 21(11), 3669; https://0-doi-org.brum.beds.ac.uk/10.3390/s21113669 - 25 May 2021

Cited by 8 | Viewed by 2365

Abstract

Multiple coincidence events from charge-sharing and fluorescent cross-talk are typical drawbacks in room-temperature semiconductor pixel detectors. The mitigation of these distortions in the measured energy spectra, using charge-sharing discrimination (CSD) and charge-sharing addition (CSA) techniques, is always a trade-off between counting efficiency and energy resolution. The energy recovery of multiple coincidence events is still challenging due to the presence of charge losses after CSA. In this work, we will present original techniques able to correct charge losses after CSA even when multiple pixels are involved. Sub-millimeter cadmium–zinc–telluride (CdZnTe or CZT) pixel detectors were investigated with both uncollimated radiation sources and collimated synchrotron X rays, at energies below and above the K-shell absorption energy of the CZT material. These activities are in the framework of an international collaboration on the development of energy-resolved photon counting (ERPC) systems for spectroscopic X-ray imaging up to 150 keV. Full article

(This article belongs to the Special Issue Room Temperature Semiconductor Detectors: Development and Applications)

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25 pages, 1517 KiB

Open AccessArticle

Charge Sharing and Charge Loss in High-Flux Capable Pixelated CdZnTe Detectors

by Kjell A. L. Koch-Mehrin, Sarah L. Bugby, John E. Lees, Matthew C. Veale and Matthew D. Wilson

Sensors 2021, 21(9), 3260; https://0-doi-org.brum.beds.ac.uk/10.3390/s21093260 - 08 May 2021

Cited by 14 | Viewed by 2853

Abstract

Cadmium zinc telluride (CdZnTe) detectors are known to suffer from polarization effects under high photon flux due to poor hole transport in the crystal material. This has led to the development of a high-flux capable CdZnTe material (HF-CdZnTe). Detectors with the HF-CdZnTe material have shown promising results at mitigating the onset of the polarization phenomenon, likely linked to improved crystal quality and hole carrier transport. Better hole transport will have an impact on charge collection, particularly in pixelated detector designs and thick sensors (>1 mm). In this paper, the presence of charge sharing and the magnitude of charge loss were calculated for a 2 mm thick pixelated HF-CdZnTe detector with 250 μm pixel pitch and 25 μm pixel gaps, bonded to the STFC HEXITEC ASIC. Results are compared with a CdTe detector as a reference point and supported with simulations from a Monte-Carlo detector model. Charge sharing events showed minimal charge loss in the HF-CdZnTe, resulting in a spectral resolution of 1.63 ± 0.08 keV Full Width at Half Maximum (FWHM) for bipixel charge sharing events at 59.5 keV. Depth of interaction effects were shown to influence charge loss in shared events. The performance is discussed in relation to the improved hole transport of HF-CdZnTe and comparison with simulated results provided evidence of a uniform electric field. Full article

(This article belongs to the Special Issue Room Temperature Semiconductor Detectors: Development and Applications)

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14 pages, 2492 KiB

Open AccessArticle

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

by Stergios Tsigaridas, Silvia Zanettini, Manuele Bettelli, Nicola Sarzi Amadè, Davide Calestani, Cyril Ponchut and Andrea Zappettini

Sensors 2021, 21(9), 2932; https://0-doi-org.brum.beds.ac.uk/10.3390/s21092932 - 22 Apr 2021

Cited by 2 | Viewed by 2409

Abstract

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

m m

and 2

m m

. 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

10^{6}

photons

m m^{- 2} s^{- 1}

. Full article

(This article belongs to the Special Issue Room Temperature Semiconductor Detectors: Development and Applications)

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22 pages, 9350 KiB

Open AccessArticle

Characterization of Chromium Compensated GaAs Sensors with the Charge-Integrating JUNGFRAU Readout Chip by Means of a Highly Collimated Pencil Beam

by Dominic Greiffenberg, Marie Andrä, Rebecca Barten, Anna Bergamaschi, Martin Brückner, Paolo Busca, Sabina Chiriotti, Ivan Chsherbakov, Roberto Dinapoli, Pablo Fajardo, Erik Fröjdh, Shqipe Hasanaj, Pawel Kozlowski, Carlos Lopez Cuenca, Anastassiya Lozinskaya, Markus Meyer, Davide Mezza, Aldo Mozzanica, Sophie Redford, Marie Ruat, Christian Ruder, Bernd Schmitt, Dhanya Thattil, Gemma Tinti, Oleg Tolbanov, Anton Tyazhev, Seraphin Vetter, Andrei Zarubin and Jiaguo Zhang Show full author list Hide full author list

Sensors 2021, 21(4), 1550; https://0-doi-org.brum.beds.ac.uk/10.3390/s21041550 - 23 Feb 2021

Cited by 16 | Viewed by 3259

Abstract

Chromium compensated GaAs or GaAs:Cr sensors provided by the Tomsk State University (Russia) were characterized using the low noise, charge integrating readout chip JUNGFRAU with a pixel pitch of 75 × 75 µm² regarding its application as an X-ray detector at synchrotrons sources or FELs. Sensor properties such as dark current, resistivity, noise performance, spectral resolution capability and charge transport properties were measured and compared with results from a previous batch of GaAs:Cr sensors which were produced from wafers obtained from a different supplier. The properties of the sample from the later batch of sensors from 2017 show a resistivity of 1.69 × 10⁹ Ω/cm, which is 47% higher compared to the previous batch from 2016. Moreover, its noise performance is 14% lower with a value of (101.65 ± 0.04) e⁻ ENC and the resolution of a monochromatic 60 keV photo peak is significantly improved by 38% to a FWHM of 4.3%. Likely, this is due to improvements in charge collection, lower noise, and more homogeneous effective pixel size. In a previous work, a hole lifetime of 1.4 ns for GaAs:Cr sensors was determined for the sensors of the 2016 sensor batch, explaining the so-called “crater effect” which describes the occurrence of negative signals in the pixels around a pixel with a photon hit due to the missing hole contribution to the overall signal causing an incomplete signal induction. In this publication, the “crater effect” is further elaborated by measuring GaAs:Cr sensors using the sensors from 2017. The hole lifetime of these sensors was 2.5 ns. A focused photon beam was used to illuminate well defined positions along the pixels in order to corroborate the findings from the previous work and to further characterize the consequences of the “crater effect” on the detector operation. Full article

(This article belongs to the Special Issue Room Temperature Semiconductor Detectors: Development and Applications)

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19 pages, 1504 KiB

Open AccessArticle

The Spectral X-ray Imaging Data Acquisition (SpeXIDAQ) Framework

by Frederic Van Assche, Sander Vanheule, Luc Van Hoorebeke and Matthieu N. Boone

Sensors 2021, 21(2), 563; https://0-doi-org.brum.beds.ac.uk/10.3390/s21020563 - 14 Jan 2021

Cited by 11 | Viewed by 2435

Abstract

Photon counting X-ray imagers have found their way into the mainstream scientific community in recent years, and have become important components in many scientific setups. These camera systems are in active development, with output data rates increasing significantly with every new generation of devices. A different class of PCD (Photon Counting Detector) devices has become generally available, where camera data output is no longer a matrix of photon counts but instead direct measurements of the deposited charge per pixel in every frame, which requires significant off-camera processing. This type of PCD, called a hyperspectral X-ray camera due to its fully spectroscopic output, yet again increases the demands put on the acquisition and processing backend. Not only are bandwidth requirements increased, but the need to do extensive data processing is also introduced with these hyperspectral PCD devices. To cope with these new developments the Spectral X-ray Imaging Data Acquisition framework (SpeXIDAQ) has been developed. All aspects of the imaging pipeline are handled by the SpeXIDAQ framework: from detector control and frame grabbing, to processing, storage and live visualisation during experiments. Full article

(This article belongs to the Special Issue Room Temperature Semiconductor Detectors: Development and Applications)

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11 pages, 3149 KiB

Open AccessArticle

Characteristics of a Hybrid Detector Combined with a Perovskite Active Layer for Indirect X-ray Detection

by Hailiang Liu, Jehoon Lee and Jungwon Kang

Sensors 2020, 20(23), 6872; https://0-doi-org.brum.beds.ac.uk/10.3390/s20236872 - 01 Dec 2020

Cited by 7 | Viewed by 2544

Abstract

In this study, we investigated the characteristics of an organic-inorganic hybrid indirect-type X-ray detector with a CH₃NH₃PbI₃ (MAPbI₃) perovskite active layer. A layer with a thickness of 192 nm annealed at 100 °C showed higher absorption, higher crystallinity, and lower surface roughness than did perovskite layers made under different conditions. In the indirect X-ray detector, a scintillator coupled with the detector to convert X-ray photons to visible photons, and the converted photons were absorbed by the active layer to generate charge carriers. The detector with the optimized MAPbI₃ (192 nm thick and 100 °C annealing condition) active layer was coupled with a CsI(Tl) scintillator which consisted of 400 μm thick CsI and 0.5 mm thick Al, and achieved the highest sensitivity, i.e., 2.84 mA/Gy·cm². In addition, the highest short-circuit current density (J_SC), i.e., 18.78 mA/cm², and the highest mobility, i.e., 2.83 × 10⁻⁴ cm²/V·s, were obtained from the same detector without the CsI(Tl) scintillator. Full article

(This article belongs to the Special Issue Room Temperature Semiconductor Detectors: Development and Applications)

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13 pages, 4232 KiB

Open AccessArticle

A Study on an Organic Semiconductor-Based Indirect X-ray Detector with Cd-Free QDs for Sensitivity Improvement

by Jehoon Lee, Hailiang Liu and Jungwon Kang

Sensors 2020, 20(22), 6562; https://0-doi-org.brum.beds.ac.uk/10.3390/s20226562 - 17 Nov 2020

Cited by 5 | Viewed by 2472

Abstract

In this paper, we studied the optimized conditions for adding inorganic quantum dots (QD) to the P3HT:PC₇₀BM organic active layer to increase the sensitivity of the indirect X-ray detector. Commonly used QDs are composed of hazardous substances with environmental problems, so indium phosphide (InP) QDs were selected as the electron acceptor in this experiment. Among the three different sizes of InP QDs (4, 8, and 12 nm in diameter), the detector with 4 nm InP QDs showed the highest sensitivity, of 2.01 mA/Gy·cm². To further improve the sensitivity, the QDs were fixed to 4 nm in diameter and then the amount of QDs added to the organic active layer was changed from 0 to 5 mg. The highest sensitivity, of 2.26 mA/Gy·cm², was obtained from the detector with a P3HT:PC₇₀BM:InP QDs (1 mg) active layer. In addition, the highest mobility, of 1.69 × 10⁻⁵ cm²/V·s, was obtained from the same detector. Compared to the detector with the pristine P3HT:PC₇₀BM active layer, the detector with a P3HT:PC₇₀BM:InP QDs (1 mg) active layer had sensitivity that was 61.87% higher. The cut-off frequency of the P3HT:PC₇₀BM detector was 21.54 kHz, and that of the P3HT:PC₇₀BM:InP QDs (1 mg) detector was 26.33 kHz, which was improved by 22.24%. Full article

(This article belongs to the Special Issue Room Temperature Semiconductor Detectors: Development and Applications)

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24 pages, 4082 KiB

Open AccessArticle

CdTe Based Energy Resolving, X-ray Photon Counting Detector Performance Assessment: The Effects of Charge Sharing Correction Algorithm Choice

by Oliver L. P. Pickford Scienti, Jeffrey C. Bamber and Dimitra G. Darambara

Sensors 2020, 20(21), 6093; https://0-doi-org.brum.beds.ac.uk/10.3390/s20216093 - 27 Oct 2020

Cited by 4 | Viewed by 2814

Abstract

Most modern energy resolving, photon counting detectors employ small (sub 1 mm) pixels for high spatial resolution and low per pixel count rate requirements. These small pixels can suffer from a range of charge sharing effects (CSEs) that degrade both spectral analysis and imaging metrics. A range of charge sharing correction algorithms (CSCAs) have been proposed and validated by different groups to reduce CSEs, however their performance is often compared solely to the same system when no such corrections are made. In this paper, a combination of Monte Carlo and finite element methods are used to compare six different CSCAs with the case where no CSCA is employed, with respect to four different metrics: absolute detection efficiency, photopeak detection efficiency, relative coincidence counts, and binned spectral efficiency. The performance of the various CSCAs is explored when running on systems with pixel pitches ranging from 100 µm to 600µm, in 50 µm increments, and fluxes from 10⁶ to 10⁸ photons mm⁻² s⁻¹ are considered. Novel mechanistic explanations for the difference in performance of the various CSCAs are proposed and supported. This work represents a subset of a larger project in which pixel pitch, thickness, flux, and CSCA are all varied systematically. Full article

(This article belongs to the Special Issue Room Temperature Semiconductor Detectors: Development and Applications)

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20 pages, 8276 KiB

Open AccessArticle

Characterization of the Uniformity of High-Flux CdZnTe Material

by Matthew Charles Veale, Paul Booker, Simon Cross, Matthew David Hart, Lydia Jowitt, John Lipp, Andreas Schneider, Paul Seller, Rhian Mair Wheater, Matthew David Wilson, Conny Christoffer Tobias Hansson, Krzysztof Iniewski, Pramodha Marthandam and Georgios Prekas

Sensors 2020, 20(10), 2747; https://0-doi-org.brum.beds.ac.uk/10.3390/s20102747 - 12 May 2020

Cited by 37 | Viewed by 3988

Abstract

Since the late 2000s, the availability of high-quality cadmium zinc telluride (CdZnTe) has greatly increased. The excellent spectroscopic performance of this material has enabled the development of detectors with volumes exceeding 1 cm³ for use in the detection of nuclear materials. CdZnTe is also of great interest to the photon science community for applications in X-ray imaging cameras at synchrotron light sources and free electron lasers. Historically, spatial variations in the crystal properties and temporal instabilities under high-intensity irradiation has limited the use of CdZnTe detectors in these applications. Recently, Redlen Technologies have developed high-flux-capable CdZnTe material (HF-CdZnTe), which promises improved spatial and temporal stability. In this paper, the results of the characterization of 10 HF-CdZnTe detectors with dimensions of 20.35 mm × 20.45 mm × 2.00 mm are presented. Each sensor has 80 × 80 pixels on a 250-μm pitch and were flip-chip-bonded to the STFC HEXITEC ASIC. These devices show excellent spectroscopic performance at room temperature, with an average Full Width at Half Maximum (FWHM) of 0.83 keV measured at 59.54 keV. The effect of tellurium inclusions in these devices was found to be negligible; however, some detectors did show significant concentrations of scratches and dislocation walls. An investigation of the detector stability over 12 h of continuous operation showed negligible changes in performance. Full article

(This article belongs to the Special Issue Room Temperature Semiconductor Detectors: Development and Applications)

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9 pages, 1811 KiB

Open AccessArticle

A Prototype VP-PET Imaging System Based on Highly Pixelated CdZnTe Detectors

by Yongzhi Yin, Yingguo Li, Tianguan Wang, Chuan Huang, Zhenqian Ye and Gongping Li

Sensors 2020, 20(5), 1294; https://0-doi-org.brum.beds.ac.uk/10.3390/s20051294 - 27 Feb 2020

Cited by 2 | Viewed by 2557

Abstract

We investigated a prototype virtual-pinhole positron emission tomography (PET) system for small-animal imaging applications. The PET detector modules were made up of 1.3 mm lutetium-yttrium oxyorthosilicate (LYSO) arrays, and the insert detectors consisted of 0.6 mm pixelated cadmium zinc telluride (CdZnTe). To validate the imaging experiment, we did a Monte Carlo simulation for the virtual-pinhole PET (VP-PET) system in the Geant4 Application for Emission Tomography (GATE). For a point source of ²²Na with a 0.5 mm diameter, the filtered back-projection algorithm-reconstructed PET image showed a resolution of 0.7 mm full-width-at-half-maximum. The system sensitivity was 0.46 cps/kBq at the center of the field view of the PET system with a source activity of 0.925 MBq and an energy window of 350 to 650 keV. A rod source phantom and a Derenzo phantom with ¹⁸F were also simulated to investigate the PET imaging ability. GATE simulation indicated that sources with 0.5 mm diameter could be clearly detected using 0.6 mm pixelated CdZnTe detectors as insert devices in a VP-PET system. Full article

(This article belongs to the Special Issue Room Temperature Semiconductor Detectors: Development and Applications)

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Review

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20 pages, 6367 KiB

Open AccessReview

CdTe X/γ-ray Detectors with Different Contact Materials

by Volodymyr Gnatyuk, Olena Maslyanchuk, Mykhailo Solovan, Viktor Brus and Toru Aoki

Sensors 2021, 21(10), 3518; https://0-doi-org.brum.beds.ac.uk/10.3390/s21103518 - 18 May 2021

Cited by 21 | Viewed by 3762

Abstract

Different contact materials and optimization of techniques of their depositions expand the possibilities to obtain high performance room temperature CdTe-based X/γ-ray detectors. The heterostructures with ohmic (MoO_x) and Schottky (MoO_x, TiO_x, TiN, and In) contacts, created by DC reactive magnetron sputtering and vacuum thermal evaporation, as well as In/CdTe/Au diodes with a p-n junction, formed by laser-induced doping, have been developed and investigated. Depending on the surface pre-treatment of semi-insulating p-CdTe crystals, the deposition of a MoO_x film formed either ohmic or Schottky contacts. Based on the calculations and I-V characteristics of the Mo-MoO_x/p-CdTe/MoO_x-Mo, In/p-CdTe/MoO_x-Mo, Ti-TiO_x/p-CdTe/MoO_x-Mo, and Ti-TiN/p-CdTe/MoO_x-Mo Schottky-diode detectors, the current transport processes were described in the models of the carrier generation–recombination within the space-charge region (SCR) at low bias, and space-charge limited current incorporating the Poole–Frenkel effect at higher voltages, respectively. The energies of generation–recombination centers, density of trapping centers, and effective carrier lifetimes were determined. Nanosecond laser irradiation of the In electrode, pre-deposited on the p-CdTe crystals, resulted in extending the voltage range, corresponding to the carrier generation–recombination in the SCR in the I-V characteristics of the In/CdTe/Au diodes. Such In/CdTe/Au p-n junction diode detectors demonstrated high energy resolutions (7%@59.5 keV, 4%@122 keV, and 1.6%@662 keV). Full article

(This article belongs to the Special Issue Room Temperature Semiconductor Detectors: Development and Applications)

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Other

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14 pages, 4896 KiB

Open AccessLetter

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

by Nicola Sarzi Amadè, Manuele Bettelli, Nicola Zambelli, Silvia Zanettini, Giacomo Benassi and Andrea Zappettini

Sensors 2020, 20(24), 7316; https://0-doi-org.brum.beds.ac.uk/10.3390/s20247316 - 19 Dec 2020

Cited by 3 | Viewed by 2512

Abstract

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 [...] Read more.

The analysis of

γ

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 (

^{241}

Am,

^{57}

Co,

^{137}

Cs and

^{133}

Ba) 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. Full article

(This article belongs to the Special Issue Room Temperature Semiconductor Detectors: Development and Applications)

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12 pages, 2845 KiB

Open AccessLetter

Influence of Surface and Bulk Defects on Contactless Resistivity Measurements of CdTe and Related Compounds

by Jan Franc, Roman Grill and Jakub Zázvorka

Sensors 2020, 20(15), 4347; https://0-doi-org.brum.beds.ac.uk/10.3390/s20154347 - 04 Aug 2020

Viewed by 2330

Abstract

We analyzed the influence of parameters of deep levels in the bulk and conditions on the surface on transient charge responses of semi-insulating samples (CdTe and GaAs). We studied the dependence on the applied bias step used for the experimental evaluation of resistivity in contactless measurement setups. We used simulations based on simultaneous solutions of 1D drift diffusion and Poisson’s equations as the main investigation tool. We found out that the resistivity can be reliably determined by the transient contactless method in materials with a large density of deep levels in the bulk (e.g., semi-insulating GaAs) when the response curve is described by a single exponential. In contrast, the materials with the low deep-level density, like semiconductor radiation detector materials (e.g., CdTe, CdZnTe, etc.), usually exhibit a complex response to applied bias, depending on the surface conditions. We show that a single exponential fit does not represent the true relaxation time and resistivity, in this case. A two-exponential fit can be used for a rough estimate of bulk material resistivity only in a limit of low-applied bias, when the response curve approaches a single-exponential shape. A decreasing of the bias leads to a substantially improved agreement between the evaluated and true relaxation time, which is also consistent with the approaching of the relaxation curve to the single-exponential shape. Full article

(This article belongs to the Special Issue Room Temperature Semiconductor Detectors: Development and Applications)

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