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Quaternary Cd0.9Zn0.1Te1– y Se y (CZTS) single crystals, a novel room-temperature nuclear radiation detector semiconductor material, have been grown using a modified vertical Bridgman method (VBM) and a traveling heater method (THM). The percentage concentration of selenium in the VBM-grown crystal was 3% and that in the THM-grown crystal was 2%. While the THM Frisch collar detector ( $4.4\times 4.4\times10.7$ mm $^{3}$ ) produced a highly resolved pulse height spectra (PHS) with a resolution of ~1.06% for 662-keV gamma rays without any correction, the VBM-grown detector ( $10\times 10\times 2$ mm $^{3}$ ) offered a high-energy resolution of ~2% after the application of a digital bi-parametric correction. The high-resolution performance of these detectors has been attributed to the addition of Se in the Cd0.9Zn0.1Te (CZT) matrix. Ab-initio calculations based on density functional theory (DFT) also confirmed that the addition of Se in the CZT matrix helps to reduce the formation of TeCd and the TeZn antisites. The VBM-grown crystals were characterized using powder X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS). While the XRD results revealed sharp diffraction peaks confirming the crystalline nature of the grown crystal, the EDS results confirmed the targeted stoichiometry of the elemental composition. The bulk resistivity of the grown crystal was calculated to be $\sim 3\times 10^{10}\,\,\Omega$ -cm from the current–voltage characteristics recorded at room temperature in a planar configuration, ensuring that the grown CZTS crystals have low dark current as required for detector-grade crystals.

Semiconductor nuclear radiation detectors made from tertiary and quaternary compounds of cadmium telluride (CdTe) can operate at room temperature without cryogenic cooling. One of such materials that have become of great interest is cadmium zinc telluride selenide (CdZnTeSe). Compared to other CdTe-based materials, such as cadmium zinc telluride (CdZnTe), CdZnTeSe can be grown with much less Te inclusions and sub-grain boundary networks. Chemical etching is often used to smoothen wafer surfaces during detector fabrication. This paper presents the characterization of CdZnTeSe that is chemically etched using bromine methanol solution. Infrared imaging shows that the wafer has no sub-grain boundary networks that often limit detector performance. The current-voltage (I-V) characterization experiment gave a resistivity of 4.6 × 1010 Ω-cm for the sample. The I-V curve was linear in the ±10 to ±50 volts range. An energy resolution of 7.2% was recorded at 100 V for the 59.6-keV gamma line of 241Am.

The electrical and spectrometric characteristics of the Cr/cadmium telluride (CdTe)/Pt structure with a metal–semiconductor type rectifying contact, used in X/ $\gamma $ -ray detectors, are investigated. For the detectors fabrication, chlorine-doped CdTe crystals with a resistivity of (3–6) $\times 10^{{9}}\,\,\Omega $ cm at 293 K were used. 137Cs spectra and their modification by applied voltage change were obtained. The reverse bias voltage corresponding to the best energy resolution of the Cr/CdTe/Pt structure is experimentally determined. The concentration of impurities N in the crystal, which determines the thickness of the space-charge region, is estimated. An energy resolution deterioration of the Cr/CdTe/Pt structure with increasing voltage is explained due to the Gunn effect.

Cadmium zinc telluride selenide (CdZnTeSe) is a new semiconductor material for gamma-ray detection and spectroscopy applications at room temperature. It has very high crystal quality compared to similar materials such as cadmium telluride and cadmium zinc telluride. The consistency of peak position in radiation detection devices is important to practical applications. In this paper, we have characterized a CdZnTeSe planar detector for bias voltages in the range of -20 V to -200 V and amplifier shaping time of 2, 3 and 6 μs. The peak position of the 59.6-keV gamma line of 241Am becomes more stable as the absolute value of the applied voltage increases. The best energy resolution of 8.5% was obtained for the 59.6-keV gamma peak at -160 V bias voltage and 3-μs shaping time. The energy resolution was relatively stable in the -120 V to -200 V range for a 6-μs shaping time. Future work will be focused on the study of the peak position and energy resolution over time.

Wide bandgap semiconductor materials capable of detecting X-rays and gamma-rays at room temperature without cryogenic cooling have great advantages that include portability and wide-area deployment in nuclear and radiological threat defense. Additional major applications include medical imaging, spectroscopy, and astrophysics. Most current room-temperature ionizing radiation detector devices are fabricated from cadmium telluride (CdTe) and cadmium zinc telluride (CdZnTe). Cadmium zinc telluride selenide (CdZnTeSe or CZTS) can be grown with high crystal yield compared to CdTe and CdZnTe. Thus, CZTS has the advantage of lowering the cost of room-temperature nuclear detectors. Thick CdTe-based detectors are prone to the trapping of charge carriers, thus limiting energy resolution and efficiency. A Frisch-Grid configuration helps to solve this problem. This research is focused on optimizing the Frisch-grid configuration for a CZTS detector. The CZTS was grown by traveling heater method. Infrared images of the CZTS matrix largely showed the absence of tellurium inclusions. The resistivity of the CZTS obtained from a current-voltage plot is of the order of 1010 Ω.cm. The charge-transport characterized by measuring the electron mobility-lifetime product is 4.7 × 10-3 cm2/V. Detector resolution was measured for various Frisch-ring widths. For a 4.8 × 4.9 × 9.7 mm3 detector, the best Frisch-ring widths were found to be 3-4 mm. A detector resolution of 1.35% full-width-at-half-maximum was obtained for the 3-mm width at -2300 V bias voltage for the 662-keV gamma peak of 137Cs. A resolution of 1.36% was obtained for the 4-mm width at -1800 V applied bias.

The design and technology of photodiodes manufacturing with a potential barrier as Schottky contact based on a substrate of radiation-resistant n-Hg3In2Te6 single crystal are presented. The photosensitivity of the photodetector covers the wavelength range λ≈0.6-1.6 μm at the maximum current monochromatic sensitivity Sλ≈1.15 A/wt for the λmax≈1.55 μm. To study the effect of contact material on the effect of the absorbed dose of ionizing radiation, two types of photodetectors Ni/n-Hg3In2Te6/In and Cr/n-Hg3In2Te6/Cr were fabricated. A study of the effect of absorbed doses of ionizing radiation Dγ1≈105 , Dγ2≈106 і Dγ3≈107 Gray on the main parameters of photodetectors: Sλ, λmax, dark currents at forward and reverse bias, open circuit voltage, short circuit current. Photodiodes, based on mercury-indium telluride (HgInTe), showed high resistance to ionizing radiation. The best resistance to ionizing radiation was shown by Cr/HgInTe/Cr photodiodes, which slightly changed their basic parameters at the absorbed dose of Dγ3≈107 Gray. Ni/HgInTe/In photodetectors lost their function after exposure to an absorbed dose of Dγ3≈107 Gray. In Ni/HgInTe/In photodetectors the absorbed dose of Dγ3≈107 Gray practically destroyed the indium contact. 30-50 % of nickel front contact was also destroyed. For comparison, similar studies were performed with photodetectors based on cadmium telluride Cr/CdTe/In, prepared by the authors and silicon too. As silicon-based photodetectors the industrial photodiodes were used.

We report the implementation of a deep convolutional neural network to train a high-resolution room-temperature CdZnTeSe based gamma ray spectrometer for accurate and precise determination of gamma ray energies for radioisotope identification. The prototype learned spectrometer consists of a NI PCI 5122 fast digitizer connected to a pre-amplifier to recognize spectral features in a sequence of data. We used simulated preamplifier pulses that resemble actual data for various gamma photon energies to train a CNN on the equivalent of 90 seconds worth of data and validated it on 10 seconds worth of simulated data.

The quest for cost-effective, high-performing radiation detector materials operable at ambient temperature has continued for more than three decades. One key to lower the overall detector cost of production is a high degree of compositional homogeneity. Spatial homogeneity of the charge-transport properties of the detector material is also essential for increasing the yield and active volume of high-performance detectors. Despite its commercial success as a room-temperature radiation detection material, CdZnTe (or CZT) suffers from a lack of compositional homogeneity on both micro- and macroscale and the presence of spatial inhomogeneity in the material’s charge-transport properties. The underlying reasons for the spatial inhomogeneity in the charge-transport properties of CZT are the presence of high concentrations of sub-grain boundary (dislocation walls) networks and secondary phases (Te-rich inclusions) on a microscale and the segregation of zinc during growth on a macroscale. This book chapter focuses on the presence of performance-limiting defects in CZT that hinder the yield and cost of high-quality detectors and have restricted widespread deployment for a variety of potential applications, particularly for uses of large-volume detectors where the demands on material perfection are significantly greater. In the recent past, the addition of selenium in CZT matrix was found to be very effective in a drastic reduction of Te-rich secondary phases and dislocation networks, while demonstrating little or no Se segregation during ingot growth. This chapter provides an overview of recent developments on the quaternary CdZnTeSe material as a potential next-generation detector material operable at room temperature.

We report on the results from testing CdZnTe (CZT) position-sensitive virtual Frisch-grid (VFG) detectors and a prototype of a 16x16 detector array proposed for a high-energy gamma ray imaging space telescope. Previously, we evaluated the spectroscopic performance of these detectors. Here, we present results from our detector performance studies with an emphasis on position resolution. We employed digital waveform capturing and analog ASIC based approaches to read out the signals from the detectors and evaluate their spectral- and spatial-resolution. The VFG arrays allow for the flexibility to scale-up the dimensions of the detectors for the desired efficiency, while the position information allows for correcting the detectors’ response non-uniformities caused by crystal defects and device geometry, thereby reducing the instrument cost and making them more feasible for emerging applications in gamma-ray astronomy, nonproliferation, portal screening and nuclear safeguards, where large

Radiation detectors, especially for X- and gamma-rays, are being developed rapidly that utilize the advantages of semiconductor detectors operating at room temperature. CdTe and CdZnTe based detectors have successfully dominated the commercial market. Both the materials, however, face limitations due to the presence of high concentrations of intrinsic defects such as Te inclusions and sub-grain boundaries. In the recent years, we have observed that the addition of selenium circumvents many issues pertaining to CdTe/CdZnTe. As a result, the new quaternary material Cd1−xZnxTe1−ySey (CZTS) is emerging as a next-generation room temperature radiation detector material with the potential to supersede CdZnTe, competing in both cost and detector performance. In this presentation we will discuss the path toward optimization of the composition of the quaternary compound for the best detector performance.

Ga2O3 has recently emerged as an attractive ultrawide bandgap material for a wide range of extreme-condition sensing applications. Besides its excellent performance as a semiconductor radiation detector material, Ga2O3 also exhibits great potential as a scintillator. Its scintillation performance can be tuned through appropriate growth control and well-designed doping. In this presentation, we will report on the temperature-dependent scintillation performance of Ga2O3 with a focus on its high scintillation yield and fast decay time. These characterization results will be correlated to Ga2O3’s intrinsic properties and material processing conditions.

The effect of selenium in CdZnTe was investigated by characterizing the Cd0.9Zn0.1Te0.98Se0.02 crystal. The bandgap of Cd0.9Zn0.1Te0.98Se0.02 is smaller than Cd0.9Zn0.1Te. In addition, its value in ingot follows the zinc-segregation tendency than that of selenium. There was a recognizable difference in the amounts of compensating dopants, the distribution of Te inclusions, and the performance of the detector. The amounts of indium doping for the compensation were reduced by the addition of selenium, which provided the highest partial pressure in the melts. Thus, the generation of Cd vacancies, which is a native defect in CdZnTe, was prevented. In addition, the size of Te inclusions varied from the tip, middle, and heel of the CdZnTeSe ingot. The addition of selenium may change the thermal conductivity of CdZnTeSe melts, which is responsible for reducing the bulging of the retrograde solidus line near stoichiometry. The planar CdZnTeSe detector showed a 59.5-keV gamma peak for Am-241 with an 11% of energy resolution.

We present a study of deep levels in CdZnTeSe radiation-detection materials. The approach relies on electrical methods that combine time and temperature evolution of the electric field and electric current after switching on the bias voltage. We also applied two optical methods to study the deep levels. The first method utilizes the temperature and temporal analysis of the electric-field evolution after switching off an additional light illuminating the sample at a wavelength of 940 nm. The second method involved measuring of the electric-field spectral dependence during near infrared illumination. We compare the results with those obtained with high-quality CdZnTe detector-grade material. We conclude that the introduction of Se into the lattice leads to a shift of the second ionization level of the Cd vacancy towards the conduction band, as predicted recently by first-principles calculations based on screened hybrid functionals., 7 pages, 5 figures

Defects both microscale and nanoscale are play an important role in CdZnTe (CZT) device performance. Typical micro-scale defects such as Te inclusions were removed via a two-step annealing process, and their concentration was analyzed via IR transmission microscopy. In addition, transmission electron microscopy (TEM) measurement was employed to investigate the evolution of nano-scale defects after the annealing process. Dislocation and stacking faults were commonly observed defects in as-grown and annealed CZT. The line shape defects, which are possibly related to the stress field around dislocations, disappeared during the in-situ the annealing at 200–220 ° C. A Frisch-grid CZT detector made via the two-step annealing process exhibited improved energy resolution and low backscattering counts in Cs-137 gamma spectra.

We grew Cd1-xMnxTe crystals with a nominal composition of 5% Mn and 95% Cd using the vertical Bridgman technique. We were able to grow crystals from as-received starting material that were free of secondary phases, such as Te inclusions with a size > 1-µm diameter, without adding compensating Cd to the initial charge. The Te precipitations (size

Cadmium zinc telluride (CdZnTe) semiconductor has applications in the detection of X-rays and gamma-rays at room temperature without having to use a cooling system. Chemical etching and chemo-mechanical polishing are processes used to smoothen CdZnTe wafer during detector device fabrication. These processes reduce surface damages left after polishing the wafers. In this paper, we compare the effects of etching and chemo-mechanical polishing on CdZnTe nuclear detectors, using a solution of hydrogen bromide in hydrogen peroxide and ethylene glycol mixture. X-ray photoelectron spectroscopy (XPS) was used to monitor TeO2 on the wafer surfaces. Current-voltage and detector-response measurements were made to study the electrical properties and energy resolution. XPS results showed that the chemical etching process resulted in the formation of more TeO2 on the detector surfaces compared to chemo-mechanical polishing. The electrical resistivity of the detector is of the order of 1010 Ω-cm. The chemo-mechanical polishing process increased the leakage current more that chemical etching. For freshly treated surfaces, the etching process is more detrimental to the energy resolution compared to chemo-mechanically polishing.

The electron- and hole-transport properties in cadmium zinc telluride selenide (CZTS) crystals are studied using a laser-induced transient-current technique with pulsed and dc bias. The internal electric field profile and velocity of surface recombination are determined by Monte Carlo simulations of electron and hole transient currents combined with a numerical solution of the drift-diffusion equation coupled with Poisson's equation. Electron and hole drift mobilities of ${\ensuremath{\mu}}_{e}$ = 830 ${\mathrm{cm}}^{2}$/Vs and ${\ensuremath{\mu}}_{h}$ = 40 ${\mathrm{cm}}^{2}$/Vs, respectively, are determined. We also develop a simple technique for evaluating surface recombination directly from measured current waveforms without the need for numerical simulation. The good quality of the prepared detector at pulsed bias, with electron- and hole-mobility-lifetime products of $(\ensuremath{\mu}\ensuremath{\tau}{)}_{e}$ = 1.9 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}3}$ ${\mathrm{cm}}^{2}$/V and $(\ensuremath{\mu}\ensuremath{\tau}{)}_{h}$ = 1.4 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}4}$ ${\mathrm{cm}}^{2}$/V, respectively, are observed. The formation of a positive space charge, originating from hole injection combined with a recombination level, is found. We observe a significant position dependence of the lifetime of electrons and holes in dc bias due to hole injection. The experiment is successfully fitted by a simple model dominated by a single deep recombination level with an energy of ${E}_{t}={E}_{C}\ensuremath{-}0.73\phantom{\rule{0.2em}{0ex}}\mathrm{eV}$; concentration of 7.3 \ifmmode\times\else\texttimes\fi{} ${10}^{11}$ ${\mathrm{cm}}^{\ensuremath{-}3}$; and electron- and hole-capture cross sections of 3.5 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}14}\phantom{\rule{0.1em}{0ex}}{\mathrm{cm}}^{2}$ and 6.5 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}14}\phantom{\rule{0.2em}{0ex}}{\mathrm{cm}}^{2}$, respectively.

Both material quality and detector performance have been steadily improving over the past few years for the leading room temperature radiation detector material cadmium-zinc-telluride (CdZnTe). However, although tremendous progress being made, CdZnTe still suffers from high concentrations of performance-limiting defects, such as Te inclusions, networks of sub-grain boundaries and compositional inhomogeneity due to the higher segregation coefficient of Zn. Adding as low as 2% (atomic) Se into CdZnTe matrix was found to successfully mitigate many performance-limiting defects and provide improved compositional homogeneity. Here we report record-high performance of Virtual Frisch Grid (VFG) detector fabricated from as-grown Cd0.9Zn0.1Te0.98Se0.02 ingot grown by the Traveling Heater Method (THM). Benefiting from superior material quality, we achieved superb energy resolution of 0.77% at 662 keV (as-measured without charge-loss correction algorithms) registered at room temperature. The absence of residual thermal stress in the detector was revealed from white beam X-ray topographic images, which was also confirmed by Infra-Red (IR) transmission imaging under cross polarizers. Furthermore, neither sub-grain boundaries nor their networks were observed from the X-ray topographic image. However, large concentrations of extrinsic impurities were revealed in as-grown materials, suggesting a high likelihood for further reduction in the energy resolution after improved purification of the starting material.

We studied the spectral dependence of the Vickers microhardness HV0.025 of CdZnTe and CdZnTeSe samples upon illumination and found out that it increases over the entire applied spectral range of 1540–750 nm. We also found out that the photoconductivity and microhardness are correlated. We observed changes in the correlation diagram (change of slope and an abrupt change of HV0.025 at several wavelengths of the illuminating light). Based on measurements of the relative changes of the space charge upon illumination using the Pockels effect, we suggest that the observed spectral dependence of positive photoplastic effect in CdZnTe and CdZnTeSe can be explained by the trapping of photoinduced electrons and holes, which affects the motion of the partial dislocations. The underlying physical explanation relies on the assumption that reconstructed bonds break before dislocation glide.

In this paper, the transformations of the morphology and surface structure of CdTe crystals under the action of pulsed laser radiation and the properties of laser-optimized Schottky diode X/γ-ray detectors developed by Ni and NiO deposition onto commercially available (111) oriented CdTe:Cl wafers has been investigated. Using scanning electron and atomic force microscopy, it was shown that, depending on the energy density and laser pulse duration, the morphology, phase composition and distribution of the system of defects and inclusions in the surface areas of CdTe crystals can be optimized. The analysis of the effect of laser treatment on the electrical and spectrometric properties CdTe X/γ-ray detectors under study was also carried out.

Cadmium zinc telluride selenide (CdZnTeSe or CZTS) has proven to have great potential in the development of low-cost devices for nuclear and radiological detection applications at room temperature without cryogenic cooling. Performance limiting defects related to Te inclusions and grain boundary networks have limited the yields of detector-grade wafers from as-grown ingots of CdTe and CZT crystals, thus leading to high costs. CZTS crystals have shown much less and sometimes the absence of performance limiting Te inclusions and grain boundary networks, thus giving it a clear advantage over CdTe and CZTS. In this paper, we present results for the characterization of CdZnTeSe planar and Frisch-grid detectors. The planer detectors were used to study the effects of chemical etching using bromine methanol (BM) solution. The leakage currents were observed to be higher for the BM -etched wafer at applied voltages above 150 V. The leakage currents were similar for lower voltages. The resistivity of the material was in the order of 1010 Ω-cm. For the planar detector, energy resolution of 6.6% FWHM was obtained for the 59.6-keV gamma line of Am-241. The Frisch-grid detector gave an energy resolution of 1.1 % FWHM for the 662-keV gamma line of Cs-137.

Cadmium zinc telluride (CdZnTe) and cadmium manganese telluride (CdMnTe) semiconductor nuclear detectors have the ability to operate at room temperature without cryogenic cooling. Thus, they can be fabricated into portable nuclear detection devices that can be used at seaports and border security, and at nuclear facilities to monitor radiation levels. In this paper, we present results from the use of X-ray photoelectron spectroscopy (XPS) to study the surface compositions of CdZnTe and CdMnTe wafers. Our results showed that Cd, Te and TeO 2 are the dominant species on these materials. Zn was also present on CdZnTe wafer, and Mn is present on the CdMnTe wafer. CdZnTe samples that were etched with high-energy ion beam did not show the presence of TeO 2 on their surfaces.

Peculiarities of morphology and electric properties of X-ray and γ-ray detectors developed by graphene deposition onto commercially available (111) oriented CdTe:Cl wafers has been investigated. Laser treatment of graphene contact using millisecond YAG-laser with an energy density of 0.1–4.5 J/cm2 has been carried out in order to modify and improve their structure and phase state.

Epitaxial layers and complex heterostructures on the base of the CdTe and Cd1-xMnxTe crystals were obtained by pulsed laser irradiation both in their transparency and absorption regions. Structural perfection of the laser-epitaxial layers, transition regions and distribution of the Te and Cd inclusions in the area of the laser action were studied. Analysis of the U-V and C-V characteristics of the obtained structures indicates a decrease in influence of surface states at the hetero-boundaries as a result of laser treatment in optimal mode, and also a reduction of reverse dark current and loss current. The spectral characteristics of the laser-epitaxial structures on the base of CdTe and Cd1-xMnxTe show, that they are promising materials for X- and gamma-radiation detectors.

Large-area arrays of position-sensitive virtual Frisch-grid CdZnTe (CZT) detectors with enhanced energy resolution and high efficiency have been proposed for spectroscopy and imaging of gamma-ray sources. Here, we present the design and test results of a linear array of such detectors optimized for use in handheld instruments. There are several application areas for such detectors including uranium enrichment measurements, storage monitoring, dosimetry and other nuclear safeguards related tasks. The array configuration provides a large area with minimum number of readout channels, which potentially allows the developers to avoid using ASIC-based readout electronics by substituting it with hybrid preamplifiers followed by digitizers. The array prototype consists of 6 5 × 7 × 25 mm3 CZT detectors side-oriented with respect to the source to achieve the maximum area. Each detector is furnished with 5 mm-wide charge-sensing pads placed near the anode. As an option, the pads can be grouped together to reduce the number of readout channels. The same can be done with the cathodes. The pads signals are converted into X–Y coordinates and combined with the cathode signals (for the Z coordinates) to give 3D positional information of each interaction point. This information is used to correct the response non-uniformity caused by material inhomogeneity, which allows the developers to use standard grade (unselected) CZT crystals, while retaining high spectroscopic performance.