Papers by Author: Ai Min Wu

Abstract: P-type microcrystalline silicon films prepared by electron cyclotron resonance（ECR）PECVD are studied here. Silane diluted with Ar (SiH4/Ar=1/19) is used as a source gas and diborane (B2H6) diluted with H2 (100ppm) as doping gases. The effect of flow rate of doping gas on the microstructures and electrical properties of the films were investigated. Raman spectroscopy and X-ray diffraction were used to determine the film structure; AFM was employed to characterize the film surface topography; Hall measurements were carried out on the doped films to determine the carrier type, carrier concentration, and Hall mobility. The optical quality was measure by transmission spectrum.

Abstract: ZnO:Al thin films were deposited on glass substrates by r. f. magnetron sputtering. The crystal structures were characterized using X-ray diffraction. The electrical property and the light transmission of the ZnO:Al thin films were investigates utilizing Hall system and UV/Vis/NIR spectrophotometer. The results show that the ZnO:Al thin films prepared with the sputtering power of 100W, working pressure of 0.3Pa and substrate temperature of 250°C have the resistivity as low as 3.1×10-3Ω⋅cm and transmittance over 90% in visible region. From the GIXRD patterns, higher electrical conductivity is related to the higher ratio of I2 (103)/I(002), which is a new reasonable structure parameter to estimate the electrical property of ZnO:Al thin films.

Abstract: The silicon nitride films have been deposited by Electron Cyclotron Resonance-plasma enhanced chemical vapor deposition (ECR-PECVD) method at low temperature, and the pure nitrogen is introduced into the ECR chamber as the plasma gas, the silane(Ar diluted, Ar:SiH4=19:1) is used as precursor gas. The optimum deposition parameters of SiN films for photovoltaic application as an efficient antireflection coating(ARC) have been investigated. The actual composition of the films will be varied with the deposition conditions, such as gas flow rate ratio(N2/SiH4), substrate temperature, and microwave power. The effect of deposition parameters on the optical performance of SiN films was determined by Ellipsometry. The Si-N and N-H stretching characteristic peaks of SiN films have been observed by FTIR spectroscopy. Results shown that uniform silicon nitride films with low hydrogen content can be deposited at high deposition rate(10.7nm/min), and the refractive index increased with the increasing of substrate temperature and microwave power. The film shows good optical properties (refractive index is 2.0 or so) and satisfied surface quality (average roughness is 1.45nm) when the deposition parameter is 350oC and microwave power is 650W.

Abstract: Nitridation of Corning 7101 glass substrate and the following GaN deposition were carried out in a self-developed electron cyclotron resonance plasma enhanced metalorganic chemical vapor deposition (ECR-PEMOCVD) system equipped with in-situ reflection high-energy electron diffraction (RHEED) monitoring. RHEED pattern and X-Ray diffraction (XRD) spectrum showed that the nitridation can effectively improve the C-axis orientation of as-prepared GaN film. Atomic force microscope (AFM) analysis indicated that the average grain size increased significantly with 5 min of nitriding, but degraded as nitriding time increased. The optimum nitriding time was achieved as 5 min. The effect of nitridation on the GaN film deposition and its formation mechanism were discussed.

Abstract: High current pulsed electron beam (HCPEB) is a fairly new technique for surface modifications, including hardening, alloying and formation of metastable phases. The present contribution gives some new insights on the microstructure modifications encountered at the top surface of HCPEB treated metals. In particular, the potential of the technique for structure modifications associated with the use of the pulsed electron beam under “heating” and “melting” conditions are highlighted.

Abstract: AlN thin films have been deposited on p-(100) Si and glass substrates by pulsed bias arc ion plating at different negative substrate biases. The crystal orientation, deposition rate and mechanical property of the films were investigated by X-ray diffraction, nanoindenter and UV-VIS spectrophotometer. The results reveal that pulsed bias has a large influence on film preferred orientation, deposition rate and mechanical property. A preferred (110) orientation is observed in the film deposited at a bias of -50V. With the increase of the bias, film deposition rate decreases first sharply then wildly; Film hardness and elastic modulus first increase, then decrease and finally increases. Higher value of film harness obtained at the bias of -50V and -500V relates to the (110) preferred orientation and grain refinement respectively.

Abstract: Due to the special heating mode of High Current Pulsed Electron Beam (HCPEB) irradiation, intense stresses such as thermoelastic stress, quasi-static stress, and shock wave stress can be generated by a dynamic thermal field. A dynamic thermo-stress is the origins of these stresses. The simulations for non-melting and melting modes are respectively compared with related phenomena such as bending, surface plastic deformation, and residual stress (non-melting mode, quasi-static stress-related), crater formation, depth distribution of microhardness, fragmentation of pearlites (melting mode, shock-stress wave-related).

Abstract: The DMS GaMnN film with certain concentration of Mn and good crystal qualities has been successfully grown on the substrate of sapphire (α-Al2O3) by ECR-PEMOCVD. The graphs of RHEED presented a clear spot-like lattice and the surface was not very glossy, which showed that the GaMnN film was single crystalline and its growth model was three -dimensional island. XRD analysis showed that the film was hexagonal structure with c -Axis oriented and the crystallinity was very well. The AFM test result showed that the GaMnN films were composed of many submicron grains with the same orientation. SQUID(superconducting quantum interference device) measurement showed an apparent ferromagnetic hysteresis at room temperature, and the Curie temperature of the film was about 400k.

Abstract: In this work, we investigated the deposition of the AlN thin films on silicon (100) substrates by mid-frequency pulsed magnetron sputtering of a metal Al target in an Ar-N2 gas mixture at room temperature. The films were characterized by various means for the composition, the crystal structure, the surface morphology, and the hardness and Young’s modulus. AFM surface RMS (root mean square) roughness analysis revealed that the surface morphology has relation with the nitrogen flow rate in the Ar–N2 gas mixture. The highest surface smoothness was observed at the nitrogen flow rate of 30-50%. The phenomenon was interpreted by the action of the vapor-solid interface on the film growth, as well as the nonequilibrium processes occurred in the film growth.

Abstract: High current pulsed electron beam (HCPEB) is now becoming a promising energetic source for the surface treatment of materials. When the concentrated electron flux transferring its energy into a very thin surface layer within a short pulse time, superfast processes such as heating, melting, evaporation and consequent solidification, as well as dynamic stress field induced by an abrupt thermal distribution in the interactive zone impart surface layer with improved physicochemical and mechanical properties. The present paper reports mainly our experimental research work on this new-style technique. Investigations performed with a variety of constructional materials (aluminum, carbon and mold steel, magnesium alloys) have shown that the most pronounced changes of composition, microstructure and properties occur in the near-surface layers, while the thickness of the modified layer with improved mechanical properties (several hundreds of micrometers) is significantly greater than that of the heat-affected zone due to the propagation of stress wave. The surfaces treated with either simply several pulses of bombardment or complex techniques, such as rapid alloying by HCPEB can exhibit improved mechanical and physicochemical properties to some extent.