Cadmium Zinc Telluride Single Crystals Research Articles

Effect of a traveling magnetic field on cadmium zinc telluride growth by the traveling heater method

The growth of high-quality cadmium zinc telluride (CZT) crystals using the traveling heater method (THM) is strongly influenced by the morphology of growth interface. Here, we investigate the effect of a traveling magnetic field (TMF) on the growth of CZT single crystals by the THM using the multi-physics numerical simulation method. When no magnetic field is applied, the concave morphology of the growth interface caused by the gravity-driven natural convection is confirmed using a multi-component mass transfer model based on the Maxwell-Stefan equations. In contrast, the application of an upward TMF accelerates the flow near the crucible wall and hence the lateral flow along the growth interface, finally leading to a relatively flat growth interface. Conversely, the increase of a downward TMF intensity significantly weakens natural convection in the central melt region; particularly, when the magnetic induction strength is increased to 300 mT at a frequency of 50 Hz, the desired convex-shaped growth interface can be achieved with the appearance of strong vortices at the dissolution interface. Therefore, we conclude that both the upward and downward TMF can improve the growth interface and thereby facilitates the growth of high-quality single crystals.

Tailoring the defects and resistivity in CdZnTe single crystal via one-step annealing with CdTe compound

Defects deteriorate the optical and electronic properties of the cadmium zinc telluride (CZT) single crystal. However, the growth of defects, such as vacancies and precipitation, could not be avoided in the industrial-grade preparation of CZT single crystal. Therefore, it is crucial to explore ways to eliminate defects after growth. This paper employs one-step heat treatment with the CdTe compound as an annealing atmosphere source. After annealing, some large-size Te inclusions are eliminated in CZT crystal, but nano Te precipitates still exist. At the same time, the crystal surface becomes rougher, caused by the thermal migration of Te droplets, dislocation proliferation, and aggregation. Increasing annealing time, dislocations migrate, decompose, and interact with each other to form dislocation walls, stacking faults or terminating at the surface, reducing dislocation etch pit density. In addition, a large number of ordered phases are still found in the crystal. Single annealing with CdTe significantly improved the crystal's optical and electrical properties. After 180 h annealing, the infrared (IR) transmittance of the as-grown wafer increased from 40% to 65%, and resistivity increased from 2.2 × 109 Ω cm to 1.7 × 1011 Ω cm. Compared to reducing the Te precipitation phase, these increasements were mainly dominated by replacing point defects, like Cd vacancies.

Formation and characterization of a CuPt-A type ordered structure in cadmium zinc telluride single crystals

The CuPt-A type ordered CdZnTe phases have first been characterized comprehensively in CdZnTe single crystals. The possible crystal structure and formation mechanism of such ordered phase have been proposed based on the TEM results.

High-performance visible light photodetectors based on inorganic CZT and InCZT single crystals

Herein, the optoelectrical investigation of cadmium zinc telluride (CZT) and indium (In) doped CZT (InCZT) single crystals-based photodetectors have been demonstrated. The grown crystals were configured into photodetector devices and recorded the current-voltage (I-V) and current-time (I-t) characteristics under different illumination intensities. It has been observed that the photocurrent generation mechanism in both photodetector devices is dominantly driven by a photogating effect. The CZT photodetector exhibits stable and reversible device performances to 632 nm light, including a promotable responsivity of 0.38 AW−1, a high photoswitch ratio of 152, specific detectivity of 6.30 × 1011 Jones, and fast switching time (rise time of 210 ms and decay time of 150 ms). When doped with In, the responsivity of device increases to 0.50 AW−1, photoswitch ratio decrease to 10, specific detectivity decrease to 1.80 × 1011 Jones, rise time decrease to 140 ms and decay time increase to 200 ms. Moreover, these devices show a very high external quantum efficiency of 200% for CZT and 250% for InCZT. These results demonstrate that the CZT based crystals have great potential for visible light photodetector applications.

Temporal pulsed x-ray response of CdZnTe: In detector**Project supported by the National Natural Science Foundation of China (Grant Nos. 51702271 and U1631116), the Young and Middle-aged Teachers Education and Scientific Research Foundation of Fujian Province, China (Grant No. JAT170407), the High Level Talent Project of Xiamen University of Technology, China (Grant No.YKJ16016R), and the Fund of the State Key Laboratory

The temporal response of cadmium-zinc-telluride (CZT) crystals is evaluated at room temperature by using an ultrafast-pulsed x-ray source. The dynamics of carrier relaxation in a CZT single crystal is modeled at a microscopic level based on a multi-trapping effect. The effects of the irradiation flux and bias voltage on the amplitude and full width at half maximum (FWHM) of the transient currents are investigated. It is demonstrated that the temporal response process is affected by defect level occupation fraction. A fast photon current can be achieved under intense pulsed x-ray irradiation to be up to 2.78 × 109 photons mm−2·s−1. Meanwhile, it is found that high bias voltage could enhance carrier detrapping by suppressing the capture of structure defects and thus improve the temporal response of CZT detectors.

Selective etching reveals the migration and evolution of dislocations in annealed Cd1-xZnxTe

We report our investigation of the influence of annealing on the behavior of dislocations in CdTe and cadmium zinc telluride (CZT) crystals. The results are discussed taking into account the tellurium diffusion from inclusions. The effect of thermal treatment on the defect structure of CZT was studied by selective etching. Bissoli’s etchant was used for revealing dislocation loops, inclusions and other defects as the most effective for (111)-oriented CZT surface. The results of selective etching were evaluated by IR microscopy and AFM for a series of systematically annealed CdTe and CZT single crystals. We studied the infrequent effect of the inclusions tracking near star-like dislocation-specific locations after post-growth annealing.

VGF bulk growth, crystalline perfection and mechanical studies of CdZnTe single crystal: A detector grade materials

Bulk size (∼80 mm long and 20 mm dia.) with high quality single crystal of Cadmium Zinc Telluride (CZT) has been successfully grown by Vertical Gradient Freeze (VGF) method using five zone furnace. The powder X-ray diffraction analysis confirms the phase of CZT crystal and growth direction was found to be (111). The grown crystal was cut and polished into different pieces and crystalline perfection was studied by high-resolution X-ray diffraction (HRXRD) by employing a multicrystal X-ray diffractometer. The HRXRD study shows that the crystalline perfection of the grown crystals is quite good. The mechanical properties were carried out on the (111) face of different portions (2–1, 2-2-, 6–2, 6–4) of CZT single crystal at room temperature in the load ranging from 0.1 to 5.0 N. The load independent hardness values for 2–1, 2-2, 6–2 and 6–4 are found to be 0.62, 0.65, 0.61 and 0.55 GPa, respectively. In addition, the observed crack profile of indentation mark has been recorded and various other parameters such as dependence of crack length, fracture toughness, brittle index number, yield strength were also calculated and discussed.

Electrical conduction behavior and hopping rates estimate of cadmium zinc telluride single crystal

CdZnTe (CZT) single crystal was grown by a modified vertical Bridgman method. It was used to study the electrical conduction behavior of CZT crystal by impedance spectroscopy in the temperature range over 303–573K. The imaginary part vs real part of complex impedance plots was considered to be a semicircle indicating only bulk contributions. The value of activation energy derived from the peak of the imaginary part of electrical impedance was found to be 0.08±0.005eV, which was assigned to relate the migration and hopping of ionized Cd vacancies and Te antisites. The discrepancy between activation energy of dc electrical conductivity (0.35±0.03eV) and the activation energy (0.20±0.04eV) of hopping rates was attributed to the high ion hopping rates and low attempt frequencies. The mechanism of electrical conduction was mainly ascribed to a short range migration or hopping of charge carriers including ionized Cd vacancies and Te antisites in the CZT crystal system.

Mechanical characteristics of nanocrystalline layers containing nanotwins induced by nanogrinding of soft-brittle CdZnTe single crystals

Nanocrystalline layers containing nanotwins induced under nanogrinding of soft-brittle cadmium zinc telluride single crystals exhibit higher hardness, ductility and fracture resistance, as well as a lower friction coefficient. This is different from the damaged layer of hard-brittle silicon semiconductors and usually nanocrystalline metals. The formation mechanism of nanotwins is interpreted by the undeformed chip thickness induced grinding energy. Compressive stress is formed in the nanocrsytalline layer containing nanotwins, whereas tensile stress is generated in that without nanotwins.

Dielectric properties and relaxation behavior of the indium doped cadmium zinc telluride single crystal

Low frequency dielectric dispersion behavior of the indium doped cadmium zinc telluride single crystal has been investigated. The temperature dependent of dielectric loss shows a broadening peak at high temperatures, which is attributed to thermally activated relaxation process. The large dielectric permittivity can be attributed to the influence of the dc conductivity and the predominance of the dc conduction in low frequency region overshadows the true behavior of the imaginary part of dielectric permittivity. The contribution of dc conduction and ac conduction has also been studied. A polaron theory indicates that the dielectric relaxation of the indium doped cadmium zinc telluride crystal at high temperature is associated with the hopping localized cadmium vacancies and telluride antisites defects. The hopping energy increases from 1.204 eV at 499 K to 1.267 eV at 534 K monotonically, which is close to the thermal activation energy 1.541 eV and dc conductivity activation energy 1.239 eV.

New deformation mechanism of soft-brittle CdZnTe single crystals under nanogrinding

The deformation of cadmium zinc telluride (CZT) soft-brittle single crystals under nanogrinding was investigated using high-resolution transmission electron microscopy. In the damage layer of the ground CZT single crystals, only dislocations and nanocrystals with sizes ranging from 5 to 20 nm were observed. This result is different from those reported on the deformation of other semiconductor materials under high pressure, such as silicon and gallium arsenide, where both amorphous phases and crystallite defects were formed. © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Growth of Bi doped cadmium zinc telluride single crystals by Bridgman oscillation method and its structural, optical, and electrical analyses

The II-VI compound semiconductor cadmium zinc telluride (CZT) is very useful for room temperature radiation detection applications. In the present research, we have successfully grown Bi doped CZT single crystals with two different zinc concentrations (8 and 14 at. %) by the Bridgman oscillation method, in which one experiment has been carried out with a platinum (Pt) tube as the ampoule support. Pt also acts as a cold finger and reduces the growth velocity and enhances crystalline perfection. The grown single crystals have been studied with different analysis methods. The stoichiometry was confirmed by energy dispersive by x-ray and inductively coupled plasma mass spectroscopy analyses and it was found there is no incorporation of impurities in the grown crystal. The presence of Cd and Te vacancies was determined by cathodoluminescence studies. Electrical properties were assessed by I-V analysis and indicated higher resistive value (8.53×108 Ω cm) for the crystal grown with higher zinc concentration (with Cd excess) compare to the other (3.71×105 Ω cm).

Characterization of large single-crystal gamma-ray detectors of cadmium zinc telluride

The need for large, room-temperature gamma-ray spectrometers to be fabricated from a single crystalline section of a cadmium zinc telluride (CZT) boule was recently met by progress in crystal growth of high-resistivity material. The characterization of such large crystals provides us with an opportunity to better understand the detector physics and apply characterization techniques, which were difficult to implement and analyze on smaller crystals. In this study, metal-semiconductor-metal, planar-CZT detectors were fabricated from large (approximately 9 × 9 × 6 mm3), CZT single crystals. We have investigated the relationship between the results of the electric-field mapping via Pockels effect, photoconductivity data, and detector performance. Changes in the surface recombination and device characteristics showing departure from symmetry are caused and revealed by variations in the surface preparation.

The effects of chemical etching on the charge collection efficiency of {111} oriented Cd/sub 0.9/Zn/sub 0.1/Te nuclear radiation detectors

We report the effects of different etchants on the mobility-lifetime product (/spl mu//spl tau/) of cadmium zinc telluride (CZT). The /spl mu//spl tau/ values were obtained via the Hecht relation. The effects of surface recombination were also investigated using photoconductivity measurements. Results were obtained for a {111} oriented CZT single crystal. We find that the surfaces behave differently after etching. Values for surface recombination rates for [111]A and [111]B surfaces can vary by up to two orders of magnitudes for the same etchant. This large variation in surface recombination rates affects the charge collection efficiency and detector performance. We report surface treatments that enhance the charge collection efficiency for [111]A and [111]B surfaces. Data describing the detector response for Am/sup 241/ spectra current-voltage relationship, and bulk /spl mu//spl tau/ values and surface recombination rates are shown for different etchants.