Zhu Shifu

Electrical and γ-ray energy spectrum response properties of PbI2 crystal grown by physical vapor transport

Lead iodide single crystal was grown by physical vapor transport method. Two radiation detectors with different configurations were fabricated from the as-grown crystal. The electrical and γ-ray response properties at room temperature of the both detectors were investigated. It is found that the dark resistivity of the detectors are respectively 3 × 1010 Ω·cm for bias electric field parallel to crystal c-axis (E//c) and 2 × 108 Ω·cm for perpendicular to crystal c-axis (E⊥c). The energy spectrum response measurement shows that both detectors were sensitive to 241Am 59.5 keV γ-rays, and achieved a good energy resolution of 16.8% for the E ⊥ c-axis configuration detector with a full width at half maximum of 9.996 keV.

First-principles calculations of the elastic, electronic and optical properties of AgGaS2

Density functional theory calculations using ultrasoft pseudopotentials and the generalized gradient approximation were performed to investigate the elastic, electronic and optical properties of AgGaS2 crystals with chalcopyrite structure. The optimized structure parameters are in good agreement with the experimental data. The mechanical stability of AgGaS2 is confirmed by calculations of the elastic constants. The band structure and density of states were calculated and it is shown that the crystal is a semiconductor with a direct energy band gap of about 1.005 eV for AgGaS2. Calculations of the optical properties, namely the dielectric function, refractive index, extinction coefficient, absorption coefficient, optical reflectivity and electron energy loss spectrum, were performed for the energy range 0–25 eV. The results indicate that AgGaS2 is a promising mid-IR crystal material.

Theoretical studies of the g factors and hyperfine structure constants for Ni+ in AgGaS2 and AgGaSe2 crystals

In this paper, the high-order perturbation formulas based on the two spin-orbit coupling parameter model for the EPR g factors g(parallel to), g(perpendicular to) and hyperfine structure constants A(parallel to), A(perpendicular to) of 3d(9) ion in tetragonal tetrahedral crystals are established by a molecular orbital approach. In these formulas, the contributions to EPR parameters from both the spin-orbit coupling parameter of central 3d9 ion and that of ligands are included. By use of these formulas, the EPR parameters Delta g(parallel to)(= g(s) - g(parallel to)), Delta g(perpendicular to)( = g(s) - g(perpendicular to)), A(parallel to) and A(perpendicular to) for Ni+ in AgGaS2 and AgGaSe2 crystals are calculated. The calculated results show good agreement with the observed values. The importance of the contribution from the spin-orbit coupling of ligands to various EPR parameters is discussed

XPS Analysis and Determination of Surface Damage Layer of CdGeAs2 Single Crystal

Abstract An integral CdGeAs 2 (CGA) single crystal with the size of Φ15 mm×45 mm was obtained by the modified Bridgman method. For the reasonable application of the CGA crystal, different polishing techniques have been employed in this work. The as-grown ingot was cut and wafers with (101) plane were mechanically polished by means of metallographic abrasive papers. Then the surface element composition and valences of (101) plane on the CGA crystal were analyzed by the X-ray photoelectron spectroscopy (XPS). Finally, the wafers were chemically polished by a bromine-methanol corrosive solution. The samples chemically polished for different time were studied by X-ray diffraction (XRD) and optical microscopy. It is found that after etching by bromine-methanol solution for 50 s at room temperature, the CdGeAs 2 wafer has no scratch marks, and possesses a narrow full width at half maximum (FWHM). Meanwhile, the thickness of the surface damage layer of CdGeAs 2 wafer was also calculated.

Single Crystal Si Layers on Glass Fabricated by Hydrophilic Fusion Bonding and Smart-Cut Technology

A single crystal Si thin film on a glass substrate has been obtained successfully by hydrophilic fusion bonding and the smart-cut technology. Tensile strength testing shows that the bonded interface has strong adhesion and the bonding strength is about 8.7 MPa. Crystallinity and microstructure of the samples have been characterized by transmission electron microscopy (TEM). Electrical properties have also been investigated by Hall measurements and four-point probe. The mobility of the transferred Si layer on glass is about 122 cm2/V.s. The results show that the single-crystal silicon layer transferred onto glass by direct bonding keeps good quality for the applications of integrated circuits, transducers, and flat panel display.

Differential Thermal Analysis and Crystal Growth of CdSiP2

Thermal properties of CdSiP2 polycrystalline were studied by differential thermal analysis (DTA) technique with a quartz capillary column. It is found that the melting point and crystallization temperature of CdSiP2 are 1139 and 1126 °C, respectively, and the supercooling degree of CdSiP2 melt is evaluated to be 13 °C. According to the results of DTA, the structure of a furnace and the temperature profile of the crystal growth for CdSiP2 were optimized. A crack-free CdSiP2 crystal with 15 mm in diameter and 40 mm in length was grown by the modified vertical Bridgman (VB) method. The X-ray diffractionmeter (XRD), X-ray energy dispersive microanalysis (EDX) and infrared spectrophotometer (IR) were employed to characterize the properties of as-grown crystal. A new cleavage face of (112) was identified in XRD spectrum. The results of EDX indicate that the crystal is of good stoichiometry. The infrared transmission is up to 55% in the infrared region from 7000 to 1500 cm−1. All the characterization results show that the obtained crystal is integrated in structure and good in optical quality which can be used in devices fabrication.

Growth and Characterizations of ZnGeP2 Crystal by a Vertical Bridgman Method

Abstract ZnGeP 2 (ZGP) single crystal with size of 24 mm in diameter and 70 mm in length was grown by a modified vertical Bridgman (VB) method in a three-zone furnace. The crystal was annealed in ZnGeP 2 powder at 600 °C for 500 h. X-ray diffraction (XRD), X-ray fluorescence (XRF) and Fourier transform infrared spectrophotometry (FTIR) were employed to characterize its properties. A ZGP optical parametric oscillator (ZGP-OPO) device was fabricated from the annealed sample. Laser experiment was carried out on the device. Tunable mid-infrared laser in the range of 3∼5 μm was realized on the ZGP-OPO pumped by 2.1 μm, 7 kHz laser. All the results indicate that our grown crystal is in good quality and can be used for nonlinear optical applications.

Substitutional sites of Co2+ ions in CuGa1−xAlxSe2:Co2+ crystals

The substitutional sites of Co2+ ions in Co2+-doped CuG(1-x)Al(x)Se(2) (including CuGaSe2 where x = 0 and CuAlSe2 where x = 1) semiconductors are studied by analyzing the composition x dependence of optical spectral parameters reported in the previous literature for these materials. From the studies, we suggest that Co2+ occupy I-group cation site rather than III-group cation site. The suggestion is discussed