Xu Jiayue

Electrical and Optical Properties of Bulk ZnO Single Crystal Grown by Flux Bridgman Method

Zinc oxide (ZnO) single crystals are grown by the modified vertical Bridgman method using a PbF2 flux. The maximum size of the as-grown ZnO crystal is about 25 mm×5 mm. The transmittance of the as-grown ZnO crystal is more than 70% in the range of 600–800 nm and the optical band gap is estimated to be 3.21 eV. The photoluminescence spectrum indicates that the as-grown ZnO crystal has a very low concentration of native defects and is much closed to its stoichiometry. The electrical measurement exhibits that the ZnO crystal has low electrical resistivity of 0.02394 Ωcm−1 and a high carrier concentration of 2.10×1018 cm−3.

Growth, Mechanical and Thermal Properties of Bi4Si3O12 Single Crystals

Bi4Si3O12 (BSO) is an excellent scintillation crystal, and is becoming the desirable candidate for dual-readout calorimeters in high-energy physics. In this work, high quality BSO crystals are successfully grown by the modified Bridgman method. For the first time, its mechanical and thermal properties are investigated and compared with those of the famous scintillation crystal Bi4Ge3O12 (BGO). The Vickers hardness and fracture toughness of BSO crystal are higher than those of BGO crystal. Its specific heat, thermal diffusivity and thermal conductivity are measured to be 0.319 Jg−1K−1, 1.54 mm2s−1 and 3.29 Wm−1K−1 at 298 K, respectively. The average thermal expansion coefficient is calculated to be 7.07 × 10−6K−1 from 300 to 1173 K. Compared with BGO crystal, BSO crystal possesses larger specific heat, thermal conductivity and smaller thermal expansion. These results indicate that BSO crystals possess better mechanical and thermal properties, which will benefit its practical applications.

Mechanical Property Evaluation of GaAs Crystal for Solar Cells

The mechanical properties of Si-doped (111) GaAs crystal for solar cells are investigated by means of a microindentation technique. Vickers microhardness Hv exhibits a nonlinear relationship with the applied load. In the range of 0.1–1 kg, Hv is decreased from 5.59 GPa to 5.03 GPa. Such a phenomenon is explained on the basis of indenter penetration. The Hv value can effectively be presumed by Kicks law, and Meyers index n is calculated to be 1.90. For the fracture toughness Kc of the GaAs crystal, it also displays nonlinear behavior related to the applied load, which is caused by energy dissipation during the development process of cracks on the wafer.