Wei Min Shi

Preparation and Characterization of ZnO Nanowire Arrays Grown on Different ZnO Seed Layers by Hydrothermal Method

Due to its suitable band gap, low cost, environmental friendliness, and high electron mobility, ZnO, naturally n-type semiconductor with a wide bandgap (Eg = 3.37 eV), is widely studied, as a window layer of heterojunction solar cells. In this study, the ZnO nanowire arrays were grown on the different ZnO seed layers by hydrothermal method. X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and UV-Vis spectra were used to characterize the ZnO nanowire arrays. The results indicate the seed layer can effect the size distribution, density, crystal structure and optical properties of the nanowire arrays.

Growth of ZnS Films and Application in Heterojunction

ZnS films were prepared by radio-frequency (RF) magnetron sputtering method. The effects of substrate temperature and annealing treatment on the properties of ZnS films were studied. The ZnS films were characterized by X-ray diffraction (XRD), UV-visible spectrophotometer, and electrical measurements. The results showed that the higher substrate temperature and post-deposition annealing treatment was helpful in improving the crystalline quality of the films, and the film had an n-type conductivity. N-type ZnS films were also deposited on p-type single-crystalline silicon (Si) substrates to fabricate ZnS/ Si heterojunction. The current-voltage (I-V) characteristic of the heterojunction was examined, which showed a rectifying behavior with turn-on voltage of about 2V.

Studies on the Structure and Properties of ZnSb Thin Films Deposited under Various Sputtering Conditions

In this paper ZnSb thin films were prepared by radio frequency magnetron sputteringfrom a stoichiometric Zn4Sb3 target followed by thermal annealing. The influence of sputteringconditions on microstructure, surface morphology, crystallinity and electrical transport propertieswere investigated. For the range of sputtering power of 50 W to 125 W and working pressure of 0.7Pa, it was found that the content of compound ZnSb phase in the films as well as film crystallinitycould be enhanced greatly by increasing the sputtering power, and this effect may be reinforced bydecreasing the working pressure to 0.2 Pa. At 0.7 Pa, A maximum value of 2.99 μW/cmK2 of powerfactor measured at room temperature was obtained at 100 W. The sample prepared at the samepower and lower pressure of 0.2 Pa has a room temperature power factor of 5.46 μW/cmK2 which isalmost doubled.

The Fabrication of Fe-Doped TiCoSb Thin Films by Magnetron Sputtering and Rapid Thermal Annealing

TiCoSb-based half-Heusler compounds, which are narrow band gap semiconductors with a high Seebeck coefficient, have been intensively studied in bulk form but rarely in thin films. In this article TiFexCo1-xSb (x=0, 0.17) thin films were synthesized on n-type single crystal Si (100) and MgO (100) substrates by DC magnetron sputtering followed by rapid thermal annealing. The X-ray diffraction patterns show that Fe doping does not affect the crystallization temperature of TiCoSb phase, but seem to induce the formation of binary phases like TiSb. Hall measurements reveal that the undoped TiCoSb thin films are n-type semiconducting, while TiFe0.2Co0.8Sb turns to p-type with half-order higher carrier concentration of 1.5×1021 cm-3. The vibrating sample magnetometer spectrum indicate that the TiCoSb thin film is non-magnetic and TiFexCo1-xSb (x=0.17) is weak magnetic.

Effect of Sputtering Conditions on the Microstructures of YNiBi Thin Film

Half-Heusler compound YNiBi thin films have been prepared by direct current (DC) magnetron sputtering from an YNiBi target. The film structure and surface morphology of YNiBi thin films were analyzed with X-ray diffraction (XRD) and atomic force microscopy (AFM). The electrical properties of the films were studied by Hall measurements. XRD patterns show that the films prepared at lower sputtering pressure and higher growth temperature exhibit minimum full width at half maximum (FWHM) and maximum diffraction peaks which belong to the same family of crystal planes. Results of AFM reveal that the surface of a variety of fabricated YNiBi films is smooth and keeps good adhesion to the substrate. The increasing of substrate temperature and slightly lowering of sputtering pressure are in favor of reducing the root mean square roughness during magnetron sputtering process. The film with high crystallinity has an electrical conductivity of 938 S/cm and carrier concentration of 2.15×1021 cm-3.

Preparation and Properties of ZnO@ZnS Nano-Array Core-Shell Structure with Different Concentration of TAA

ZnO@ZnS nano-array core-shell structure was synthesized through a solution method using a thioacetamide (TAA) solution in deionized water. The as-synthesized ZnO nano-array and TAA solution were employed to supply zinc and sulfur ions to form the ZnO@ZnS core-shell structures. The properties of the structure were characterized by X-ray diffraction (XRD), Raman spectrum, scanning electron microscopy (SEM) and UV-Vis spectra. The results indicate that ZnO nano-array was coated with ZnS particles. The concentration of TAA solution can affect the diameter, surface roughness and optical properties of the ZnO@ZnS nano-array core-shell structures.

Properties of Ohmic Contact of Au Electrode on Polycrystalline Mercuric Iodide

Polycrystalline mercuric iodide films are being developed as a new detector technology for digital X-ray imaging. The properties of the contact between electrode and film play an important role in the performance of the polycrystalline mercuric iodide detector. In this paper, the films were grown on the thin film transistor (TFT) substrates via hot-wall physical vapor deposition method. Au front contacts were deposited onto the HgI2 films by thermal evaporation under a vacuum of 10-4Pa. The HgI2 films were characterized by X-ray diffraction (XRD). The surface morphology of the films before and after the process of evaporating Au was compared by scan electron microscopes (SEM). And the I-V curve was measured after evaporating Au electrode. The results indicate that the polycrystalline mercuric iodide films we prepared have a very strong (001) growth-preference. Au was deposited on the grain surface forming excellent ohmic contact with polycrystalline α-HgI2 film which was also confirmed by the I-V characteristic of HgI2 film after the process of evaporating Au electrode.

Preparation and Properties of Cu2ZnSnS4 Nanoparticles by Solvothermal Method

Earth-abundant Cu2ZnSnS4(CZTS), a promising alternative photovoltaic material, was prepare by a mild solvothermal route and annealed. The as-prepared nanoparticles were obtained at 200°C and analyzed by X-ray diffraction(XRD). The crystallinity of CZTS particles was greatly improved by annealing in N2 gas shown in XRD. EDS results indicate the composition of the film and the variety of the ratio of the metal atoms and S atoms.

Aluminum-Induced Crystalization of Amorphous Silicon Films Deposited by Megnetron Sputtering

Aluminum–induced crystallization of sputtered a-Si under two-step annealing procedure on glass substrate is studied. A 200 nm thick a-Si film was deposited by magnetron sputtering on glass and a Al film of 150 nm was sputtered on top. The samples were annealed under two-step annealing procedure. Nucleation and growth of grains were followed by optical microscopy (OM), X-ray diffraction (XRD), Raman spectroscopy, and energy dispersive spectroscopy (EDS). Continuous (111) oriented poly-Si films were obtained with a Raman Peak at 520.8cm-1. The different annealing periods is discussed.

Solution-Based Metal Induced Crystallization of Amorphous Silicon Films

A viscous Nickel (Ni) solution was applied on amorphous Si films by spin coating and its effect on the crystallization of amorphous Si films was investigated with a two-step annealing process. The experimental results show that with the help of the two-step annealing, the crystallization of the film can take place at 500oC. At the same time, the crystalline fraction gets up to 79.4% after annealing at a high temperature of 520oC and the grain size of the polycrystalline Si films is approximately 200 nm.