Jie Wanqi

Correlation between the IR transmission spectra and the CdZnTe qualities

Tens of Cd0.9Zn0.1Te wafers from three ingots grown by the vertical Bridgman method (VBM) are characterized by infrared (IR) transmission. Four types of distinct IR transmission spectra are found for these wafers. Each of them corresponds to one kind of wafers with specified qualities. At the same time, approximate mathematical relations exist between the wafer dislocation density and their IR transmissions at the wavenumber 4000 cm-1, as well as between the resistivity and the IR transmissions at the wavenumber 500 cm-1. The reasons of the above results are attempted to be given.

Atomic mobilities and diffusivities in Al alloys

Knowledge of diffusivity is a prerequisite for understanding many scientific and technological disciplines. In this paper, firstly major experimental methods, which are employed to provide various diffusivity data, are briefly described. Secondly, the fundamentals of various computational methods, including first-principles method, embedded atomic method/molecular dynamic simulation, semi-empirical approaches, and phenomenological DICTRA technique, are demonstrated. Diffusion models recently developed for order/disorder transitions and stoichiometric compounds are also briefly depicted. Thirdly, a newly established diffusivity database for liquid, fcc_A1, L12, bcc_A2, bcc_B2, and intermetallic phases in the multicomponent Al alloys is presented via a few case studies in binary, ternary and quaternary systems. And the integration of various computational techniques and experimental methods is highlighted. The reliability of this diffusivity database is validated by comparing the calculated and measured concentration profiles, diffusion paths, and Kirkendall shifts in various binary, ternary and quaternary diffusion couples. Next, the established diffusivity databases along with thermodynamic and other thermo-physical properties are utilized to simulate the microstructural evolution for Al alloys during solidification, interdiffusion and precipitation. A special discussion is presented on the phase-field simulation of interdiffusion microstructures in a series of Ni-Al diffusion couples composed of γ, γ′, and β phases under the effects of both coherent strain and external compressive force. Future orientations in the establishment of next generation of diffusivity database are finally addressed.

Effect of Al powder content on SHS Al-Ti grain refiner

Self-propagating high-temperature synthesis (SHS) was used for the preparation of Al–Ti grain refiner. Al/Ti mole ratio in initial powder mixture was varied from 0:1 to 4.5:1 for controlling adiabatic temperature, which was found to have effect on the morphology and composition of synthesised Al3Ti particles. The increase in Al powder content resulted in the adiabatic temperature rise and change of titanium aluminide morphology from needle-like to blocky.

Point defects in CdTe

Abstract A point defect model for CdTe is presented based on a selection of potentially electrically active point defects which includes V Cd , Cd i , V Te , Te i and Te Cd . The reaction energies and entropies of the defects were established. The effect of changing the Fermi energy with Cd partial pressure and temperature are then discussed in detail. The defect concentrations are given as functions of Cd partial pressure and the minimum attainable deviation in stoichiometry is derived. Through the analysis and the calculations, a specific detailed recipe for post-growth annealing is suggested.

Surface passivation and electrical properties of p-CdZnTe crystal

The electrical properties of Au/p-CdZnTe contacts with different surface treatments, especially passivation treatment, are investigated in this paper. After the passivation, a TeO2 oxide layer with a thickness of 3.1 nm on the CdZnTe surface was identified by XPS analysis. Meanwhile, photoluminescence (PL) spectra confirmed that the passivation treatment minimized the surface trap state density and decreased the deep-level defects related to recombination of Cd vacancies. Current–voltage and capacitance–voltage characteristics were measured. It was shown that the passivation treatment could increase the barrier height of the Au/p-CdZnTe contact and decrease the leakage current.

Atomic and Electronic Structures of Cd0.96Zn0.04Te(110) Surface

X-Ray diffraction is used to analyse the lattice structure of Cd0.96Zn0.04Te (CZT), and the lattice constant is measured to be 0.647 nm. The atomic structure of the clean CZT(110) surface obtained by Ar+ etching in vacuum is observed by low-energy electron diffraction, where no surface reconstruction is discovered. Angle-resolved photoemission spectroscopy was used to characterize the surface state of the clean CZT (110) surface, by which we find a 1.5-eV-wide surface band with the peak at 0.9 eV below the Fermi energy containing about 6.9×1014 electrons/cm2, approximately one electron per surface atom.

Reduction of Te-rich phases in Cd1−xZnxTe (x = 0.04) crystals

Cd1?xZnxTe crystals are annealed in Cd/Zn vapours to eliminate Te-rich phases. During the saturated Zn partial pressure annealing and the high-temperature annealing under low PZn, large Te-rich phases gather at the slice surface through thermo-migration. This process increased the stress in the bulk crystals and caused the formation of defects such as twins, stacking faults, and dislocations. The IR transmission is greatly improved by annealing the slices under saturated PZn and then removing a layer from the surface of the slices with a thickness of about 50?m. For Cd1?xZnxTe slices annealed at low temperature and low Zn partial pressure, the reduction of the Te-rich phases greatly depends on the diffusion of the atomic defects.

Modelling Ekman flow during the ACRT process with marked particles

Abstract The numerical method SOLA-VOF has been applied to the calculation of convection during the ACRT process. The Ekman flow is tracked with marked particles. The movement of the fluid adjacent to the crucible base induced by Ekman flow is shown clearly. The effects of crucible acceleration, maximum rotation rate and crucible diameter on the Ekman flow was studied. The numerical results are compared with those from siumlation experiments.

Synthesis of ZnS whiskers and their photoluminescence properties

ZnS whiskers were successfully synthesized by the chemical vapor deposition method with the assistance of CuS micro-spheres. The composition, morphology and structure of the samples were characterized by X-ray diffraction, X-ray energy dispersive spectroscopy, scanning electron microscopy, and the temperature-dependent photoluminescence (PL) spectrum over a temperature range from 10 to 250 K was studied. The results show that the as-synthesized ZnS whiskers have an average length of 0.3 mm and diameter of 2.5 μm with a cubic zinc-blende structure. There exist three emission bands in the blue, green and yellow regions, and the emission mechanism is discussed. As the temperature increases, the temperature-dependent PL spectrum shows anomalous behavior, where distinct inverted V-shaped characters of blue and green emission integrated intensity and an inconspicuous S-shape of blue emission peak energy are observed. The transition mechanism is discussed.

Formation of hot-top segregation in steel ingot and effect of steel compositions

Convection and composition variations in the liquid zone during solidification of H2O-NH4C1 solution, which has the same model of convection as that of steel ingot, are studied. It is shown that a weak convection region forms near the ingot top in the liquid zone at a certain stage of solidification and then develops downward gradually, and the negative segregation is detected in the weak convection region. This interesting phenomenon reveals the formation process of hot-top segregation in steel ingots. The parameterdpL/dfL, an important factor affecting the formation of hot-top segregation, is established as a function of the steel composition. When dpL/dfL is decreased by changing the steel composition, hot-top segregation will be impeded.