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Cd(1-x)Zn(x)Te (CZT) crystals are the leading semiconductors for radiation detection, but their application is limited by the high cost of detector-grade materials. High crystal costs primarily result from property nonuniformity that causes low manufacturing yield. Although tremendous efforts have been made in the past to reduce Te inclusions/precipitates in CZT, this has not resulted in an anticipated improvement in material property uniformity. Moreover, it is recognized that in addition to Te particles, dislocation cells can also cause electric field perturbations and the associated property nonuniformities. Further improvement of the material, therefore, requires that dislocations in CZT crystals be understood and controlled. Here, we use a recently developed CZT bond order potential to perform representative molecular dynamics simulations to study configurations, energies, and mobilities of 29 different types of possible dislocations in CdTe (i.e., x = 1) crystals. An efficient method to derive activation free energies and activation volumes of thermally activated dislocation motion will be explored. Our focus gives insight into understanding important dislocations in the material and gives guidance toward experimental efforts for improving dislocation network structures in CZT crystals.

Single crystals of [Cd.sub.0.8][Zn.sub.0.2]Te grown at the Institute of Solid State Physics, Chernogolovka, Russia, by the high-pressure vertical Bridgman method (HPVB) were mapped using X-ray fluorescence (XRF), X-ray diffraction (XRD), photoluminescence (PL), and leakage current measurements. Most of the Russian samples which we refer to as p-type CZT were more uniform in Zn composition than U.S. commercially produced material. The Russian material had a poorer crystallinity and, in the best case, could only count nuclear radiation. Differences in the material properties between Russian (p-type) and U.S. (n-type) material will be described. Index Terms - CdZnTe, high-pressure Bridgman.

CdTe and CdTe-based Cd1-xZnxTe (CZT) alloys are important semiconductor compounds that are used in a variety of technologies including solar cells, radiation detectors, and medical imaging devices. Performance of such systems, however, is limited due to the propensity of nano- and micro-scale defects that form during crystal growth and manufacturing processes. Molecular dynamics simulations offer an effective approach to study the formation and interaction of atomic scale defects in these crystals, and provide insight on how to minimize their concentrations. The success of such a modeling effort relies on the accuracy and transferability of the underlying interatomic potential used in simulations. Such a potential must not only predict a correct trend of structures and energies of a variety of elemental and compound lattices, defects, and surfaces but also capture correct melting behavior and should be capable of simulating crystalline growth during vapor deposition as these processes sample a variety of local configurations. In this paper, we perform a detailed evaluation of the performance of two literature potentials for CdTe, one having the Stillinger-Weber form and the other possessing the Tersoff form. We examine simulations of structures and the corresponding energies of a variety of elemental and compound lattices, defects, and surfaces compared to those obtained from ab initio calculations and experiments. We also perform melting temperature calculations and vapor deposition simulations. Our calculations show that the Stillinger-Weber parameterization produces the correct lowest energy structure. This potential, however, is not sufficiently transferrable for defect studies. Origins of the problems of these potentials are discussed and insights leading to the development of a more transferrable potential suitable for molecular dynamics simulations of defects in CdTe crystals are provided. [ABSTRACT FROM AUTHOR]

Based upon a many-body La–Br interatomic potential, molecular dynamics simulations have been performed to study mechanical properties of the UCl3 phase, LaBr3 crystal. Both plastic deformation and fracture mechanisms were explored. For plastic deformation, dislocation line energy, core structure, slip mechanism, and mobility were all examined. For fracture mechanism, tensile tests were conducted under different loading directions. We found that the <0001> prism dislocations have the lowest line energies (∼5 eV/Å, compared to >8 eV/Å for the <1120> basal dislocations). The <0001> edge dislocation is mobile and its mobility increases with temperature. The <0001> screw dislocation is mobile at 0 K temperature and it becomes immobile as temperature is increased. The <1120> edge and screw dislocations are always immobile at any temperatures. The mobile dislocations do not dissociate into partials and they always move in a perfect unit. The immobile dislocations, however, always exhibit nonplanar dissociated core structures. Interestingly, the slip plane of the <0001> edge dislocation differs from the cleavage plane by an one-atomic plane distance, whereas the slip of the <0001> screw dislocation is associated with alternative out-of-plane exchange of Br atoms. The critical shear stress for the onset of <0001> slip was found to be around 1 GPa for the edge dislocation at 300 K, and around 1.5 GPa for both edge and screw dislocations at 0 K. Tensile loading simulations indicated that the theoretical strength of the material is critically determined by the {1100} cleavage. The lowest theoretical strength and fracture strain occur when the loading direction is normal to the cleavage plane and the highest theoretical strength and fracture strain occur when the loading direction is parallel to the cleavage plane. [ABSTRACT FROM AUTHOR]