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Preparation of GaN Nanowires and SiC Nanowires via CVD Method and Their Characterizations

Author: LiJiaLin
Tutor: TangYuanHong
School: Hunan University
Course: Materials Physics and Chemistry
Keywords: GaN Nanowires SiC nanowires CVD method Growth Mechanism Multi - gas-solid reaction Twin structure
CLC: TB383.1
Type: Master's thesis
Year: 2009
Downloads: 302
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Abstract

Two superior performance of the wide band gap semiconductor material, gallium nitride (GaN) and silicon carbide (SiC) materials have excellent physical and chemical properties, mechanical, and optical properties of both the bulk material in the application process, has begun to show a huge advantage. Due to the one-dimensional materials with size effect, the phenomenon of quantum confinement effect, surface effect, and behave in a special physical and chemical properties, GaN and SiC material already does not stop at the bulk material, one-dimensional GaN and SiC nanomaterials Preparation and Properties of researchers has become a hot research. In the course of the study of one-dimensional GaN and SiC nanomaterials to develop a method for the preparation of one-dimensional nanowires. However, in most of the preparation process, there are still metal catalyst, reaction conditions are harsh and complicated to operate, the required equipment and raw materials expensive. Accordingly, we try to use a high temperature tube furnace under the conditions do not add any metal catalyst, was prepared by a simple operation of one-dimensional GaN nanowires and SiC nanowires. The focus of the present study was a one-dimensional GaN nanowires and SiC nanowires were prepared by chemical vapor deposition (CVD) method and the multiple gas-solid reaction product of Comparative Experimental Study on the reaction temperature, gas flow, reactants, thereby summed up the best preparation conditions, combined with the characterization results, one-dimensional GaN nanowires and SiC nanowire growth mechanism, and which special likeness to analyze. One-dimensional GaN nanowires were prepared by CVD metal gallium (Ga) and ammonia (NH3) as raw material, the optimum reaction temperature of 900 ° C, and the ammonia gas flow constant can be collected on a silicon substrate to a large number of diameter of approximately 60 nm and lengths of up to several tens of microns of the nanowire, the nanowire surface is smooth, evenly distributed. When NH3 gas stream is unstable, it will generate a large number of coarse fibrous structure having a core-sheath structure of the oxide covered, in addition to this, the residual oxygen in a quartz tube will lead to insufficient binding of the N and Ga, thus affecting the gallium nitride nanowires production. According to the results of the above analysis, we propose autocatalytic gas - solid - liquid (VLS) growth mechanism to explain the growth mechanism of GaN nanowires. Silicon, graphite and silica (SiO2) powder as a raw material through multiple gas-solid (VS) reaction was successfully prepared a one-dimensional silicon carbide (SiC) nanowires. By X-ray diffraction (XRD) analysis showed that the resulting product is the cubic structure of the beta-SiC. Observation using a scanning electron microscope (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM), the one-dimensional SiC nanowires for 30 to 50 nm, up to tens or even hundreds of microns in length, along the [111] direction of growth of monocrystalline beta-SiC nanowires. According to the results of several comparative experiments using multiple gas-solid reaction mechanism, SiC nanowires growth process and growth mechanism. We try to change the preparation-SiC nanowires reaction temperature, the silicon source and carbon source, in order to get the best experimental conditions. SiO2, graphite and silicon as a raw material at 1200 ° C is the optimal reaction temperature; silicon is one of the essential source of silicon, and more conducive to the deposition of the nanowires; 1200 ° C or under, only the introduction of SiO2 as a reactant one, in order to generate the SiC nanowires, select high purity, uniform particle size of SiO2 powder, more helpful for preparing a fine nanowire; graphite instead of carbon nanotubes as a carbon source, either to obtain an excellent product, and can be greatly reduce the cost of experiments. Can be observed in the growth process of the SiC nanowires having a a periodic twinned structure of SiC nanowires defects that appear in the one-dimensional materials based on extensive studies, we have explained the reasons for the formation of the structure and forming process.

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