Growth, Characterization and Evaluation of CdZnTeSe Single Crystals for Room Temperature Radiation Detectors

In this research work Cd0.9Zn0.1Te0.03Se0.97 (CZTS) single crystals were grown using in-house zone refined 7N (99.99999%) purity elements through vertical Bridgman (VBM) method and vertical gradient freeze (VGF) method. The morphological, compositional, and structural characteristics were then performed on the grown CZTS crystals. The x-ray diffraction (XRD) analysis on the grown crystals showed sharp diffraction peaks indicating a highly crystalline nature, with a lattice constant of ~6.45 Å. The elemental and stoichiometric ratio of the grown CZTS crystals were examined by using energy-dispersive x-ray analysis (EDX), which confirmed the formation of the quaternary compound in its desired stoichiometry. Scanning electron microscopy (SEM) on the surface of the processed (etched and polished) crystals displayed a smooth surface with no noticeable defects or cracks. The oxidation states of the precursor elements were analyzed using x-ray photoelectric spectroscopy (XPS), which was found to be relevant to the states found in the precursor compounds such as Cd0.9Zn0.1Te (CZT) and CdTe. Current-voltage characterizations were performed on the fabricated devices with 11 × 11 × 3 mm3 dimension wafer cut out from the grown ingots. The leakage current was low for crystals grown using the vertical Bridgman method (VBM) as well as for the vertical gradient freeze method (VGF). The bulk resistivity was in the range of 109 to 1010 Ω-cm and the log J – log V plots revealed a trap space charge limited current (SCLC) mechanism at moderate bias. Alpha spectroscopy using 241Am (americium radio isotope as a radiation source) was carried out to calculate the charge transport properties in the fabricated devices. The mobility-lifetime product was found to be ~1.5×10-3 cm2/V while the drift mobility was calculated to be ~710 cm2/V-s. The observed electron-transport properties were in good agreement with the reported values for the best CZTS crystals. The single pass Bridgman technique and the vertical gradient technique, used to grow the crystals can help reduce the crystal growth duration and the production cost related to large volume growth of CZTS semiconductor crystal boules, without diminishing any of the charge transport and radiation detection properties found in CZTS crystals

A CdZnTeSe Gamma Spectrometer Trained by Deep Convolutional Neural Network for Radioisotope Identification

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

High Performance Pd/4H-SiC Epitaxial Schottky Barrier Radiation Detectors for Harsh Environment Applications

Although many refractory metals have been investigated as the choice of contact metal in 4H-SiC devices, palladium (Pd) as a Schottky barrier contact for 4H-SiC radiation detectors for harsh environment applications has not been investigated adequately. Pd is a refractory metal with high material weight-to-thickness ratio and a work function as high as nickel, one of the conventional metal contacts for high performing 4H-SiC Schottky barrier detectors (SBDs). In this article, Pd/4H-SiC epitaxial SBDs have been demonstrated for the first time as a superior self-biased (0 V applied bias) radiation detector when compared to benchmark Ni/4H-SiC SBDs. The Pd/4H-SiC SBD radiation detectors showed a very high energy resolution of 1.9% and 0.49% under self- and optimized bias, respectively, for 5486 keV alpha particles. The SBDs demonstrated a built-in voltage (Vbi) of 2.03 V and a hole diffusion length (Ld) of 30.8 µm. Such high Vbi and Ld led to an excellent charge collection efficiency of 76% in the self-biased mode. Capacitance mode deep level transient spectroscopy (DLTS) results revealed that the “lifetime-killer” Z1/2 trap centers were present in the 4H-SiC epilayer. Another deep level trap was located at 1.09 eV below the conduction band minimum and resembles the EH5 trap with a concentration of 1.98 × 1011 cm−3 and capture cross-section 1.7 × 10−17 cm−2; however, the detector performance was found to be limited by charge trapping in the Z1/2 center. The results presented in this article revealed the unexplored potential of a wide bandgap semiconductor, SiC, as high-efficiency self-biased radiation detectors. Such high performance self-biased radiation detectors are poised to address the longstanding problem of designing self-powered sensor devices for harsh environment applications e.g., advanced nuclear reactors and deep space missions

Quaternary Semiconductor Cd1−xZnxTe1−ySey for High-Resolution, Room-Temperature Gamma-Ray Detection

The application of Cd0.9Zn0.1Te (CZT) single crystals, the primary choice for high-resolution, room-temperature compact gamma-ray detectors in the field of medical imaging and homeland security for the past three decades, is limited by the high cost of production and maintenance due to low detector grade crystal growth yield. The recent advent of its quaternary successor, Cd0.9Zn0.1Te1−ySey (CZTS), has exhibited remarkable crystal growth yield above 90% compared to that of ~33% for CZT. The inclusion of Se in appropriate stoichiometry in the CZT matrix is responsible for reducing the concentration of sub-grain boundary (SGB) networks which greatly enhances the compositional homogeneity and growth yield. SGB networks also host defect centers responsible for charge trapping, hence their reduced concentration ensures minimized charge trapping. Indeed, CZTS single crystals have shown remarkable improvement in electron charge transport properties and energy resolution over CZT detectors. However, our studies have found that the overall charge transport in CZTS is still limited by the hole trapping. In this article, we systematically review the advances in the CZTS growth techniques, its performance as room-temperature radiation detector, and the role of defects and their passivation studies needed to improve the performance of CZTS detectors further

Strategies of Nanomaterial Application for Enhanced Wound Curing: An Overview

The biological process of healing of wounds deals with the regeneration of cells and is of utmost importance mainly because of the morphological and functional attributes of the tissue. One of the modern approaches is to use novel nanomaterial based wound dressings and other therapeutic treatments that have higher efficiency and specificity. Researchers all around the world have established the competence of various organic, inorganic or polymer-based and biogenically synthesized nanomaterials as a weapon for wound curing. Various matrices carrying nanoparticles like hydrogels, hydrocolloids are used in nano based drug delivery system. The biocompatibility, antimicrobial efficacy and sustained rate of drug delivery are the three main features that are considered for designing a nano drug for effective wound healing. The modification of the nanosized liposome using propylene glycol increases cell-permeation and retention in skin layer. Curcumin loaded liposomes show high anti-inflammatory effect, carbon nanodots (CNDs) and graphene oxide based nanosheets have also shown an immense importance in possessing high surface area. They also show potency in promoting fibroblast growth factors and collagen deposition for speedy recovery of wound. Moreover, the chronic wounds, that could not be cured by common antibiotics, can be addressed by nano based drugs not only for their easy penetration to deeper layer of tissues but also for their efficiency in killing some biofilm associated bacterial strains. Hence, nowadays nano based dressing materials are widely used for rapid recovery of wounds of various types

Synthesis of CdZnTeSe Single Crystals for Room Temperature Radiation Detector Fabrication: Mitigation of Hole Trapping Effects Using a Convolutional Neural Network

We report the growth of Cd0.9Zn0.1Te0.97Se0.03 (CZTS) wide bandgap semiconductor single crystals for room temperature gamma-ray detection using a modified vertical Bridgman method. Charge transport properties measured in the radiation detectors, fabricated from the grown CZTS crystals, indicated signs of hole trapping. Hole traps inhibit high-resolution radiation detection especially for energetic gamma rays. In this article, we describe a deep convolutional neural network (CNN) that has demonstrated remarkable efficiency in identifying the energy of a gamma photon detected by a CZTS detector. The CNN has been trained using simulated data that resemble output pulses from actual CZTS detectors when exposed to 662-keV gamma photons. The device properties required for the simulation have been derived from radiation detection measurements on a real Cd0.9Zn0.1Te0.97Se0.03 detector fabricated in our laboratory. The CNN has been trained with detector pulses arising through photoelectric (PE) and Compton scattering (CS) separately. The percentage error in predicting the detected energies, within an extremely small duration of 0.28 ms, was found to be lower than 0.1% for gamma energies above 50 keV and for training datasets containing PE and CS events separately. The CNN was also validated for a mixed PE and CS dataset to obtain a prediction error of 1%. The effect of detector resolution on the efficiency of the CNN was also explored