Siyuan Wu, Zhe Huang, Baishan Chen, Xiao Liu, Yunzhu Ma, Yufeng Huang, Siwei Tang, Chaoping Liang, Wensheng Liu
National Key Laboratory of Science and Technology on High-strength Structural Materials, Central South University, Changsha city, Hunan province 410083, China
## Abstract
CdZnTe (CZT) has attracted much attention in nuclear detection field attribute to its high detection efficiency, high energy resolution and room-temperature operation. In this work, the CdZnTe samples were prepared by Vertical gradient method. High-resolution transmission electron microscopy (HRTEM) was used to investigate the nanoscale defects in CZT crystals. It is found that the twins are symmetric about the {111} plane, and the dislocations and stacking faults locate around the twin boundary. Te precipitations with hexagonal crystal structure is coherent with the CZT matrix. Te precipitated phases have three shapes of hexagon, polygon and irregularity, which determined by the interface energy between precipitations and matrix. The ordered phase with acicular shapes was found along [011] zone axis. The two variants of the ordered phase is corresponding to 1/2 {111} and 1/3 {111} ultrasound lattice, respectively. Besides the small angle grain boundaries with semi-coherent interface are observed. It is important to explore the behavior of nanoscale defects in the growth of CZT crystals in order to enlighten a path to regulate the nanoscale defects. The stability of the temperature interface is crucial to the preparation of high quality CZT crystals.
## Introduction
Radiation detection has been used in space exploration, biomedical imaging, high-energy physics research, radioactivity monitoring and homeland security inspection. [1] CdZnTe (CZT) show great advantages in strong ray blocking ability, high energy resolution, high signal-to-noise ratio and room-temperature operation. [2] Thus CZT has become the most promising material for room-temperature high-energy X-ray and γ-ray detector. [[3], [4], [5]]
High detection efficiency and energy resolution are the prerequisites for the application of detectors in environmental detection and medical imaging. [6] Room temperature nuclear radiation detector requires high quality CZT crystal to achieve high resistivity (>1010 Ω∙cm), high carrier mobility and long-life. [7,8] However, members of structural defects are formed in the crystal attribute to the easily deviated stoichiometric ratio, the large segregation coefficient of Zn and the unstable solid-liquid interface. [9,10] In addition, due to the low thermal conductivity and stacking fault energy, twins and faults are easily generated during the growth process. These defects will break the periodic crystal structure of CZT, lower the resistivity, and ultimately weaken the detection performance of the radiation detector. [[11], [12], [13]] Using the transient current technique, Jiangpeng Dong et al. found that twin crystals lessen the efficiency of charge collection and transport. [14] Boru Zhou discovered that the reduction of defect density could improve the resistivity of the crystal by thermally stimulated current spectra. [15]
At present, structure defects have been extensively studied in its growth mechanism, morphology evolution and theoretically calculation. [[16], [17], [18], [19]] Yadong Xu concludes that induced dislocation appear around the Te inclusion attribute to the stress release caused by the diverse thermal expansion coefficient of Te precipitation and CZT crystal. [20] Chao Xu established the growth model of inclusion defects during annealing based on atomic diffusion. [21] J.H. Greenberg summarized the P-T-X phase equilibrium data of CZT with different stoichiometric ratios through vapor pressure scanning. [9] However, investigation on structure defects is mainly confined to the analysis on the micron scale. There is few literature reported about the structure and mechanism of nanoscale defects. Thus, it is necessary to explore the investigation of the nanoscale defects further, and then provide a guidance for reduce defects density to improve the crystal quality.
In this work, we use the High-resolution transmission electron microscopy (HRTEM) to investigate the nanoscale defects in the CZT crystal grown by Vertical gradient method to reveal the structure and origin of the nanoscale defects.
CdZnTe Association (CdZnTe.com)
https://www.cdznte.com/thesis/identification-of-twin-and-nanoscale-te-precipitations-in-cdznte-crystals-grown-by-vertical-gradient-method-with-hrtem.html