Synthesis And Characterization Of GaN Nanostructures By Chemical Vapor Deposition

GaN, a direct-band-gap III–V semiconductor with large energy gap )3.4 eV atroom temperature) has stimulated growing interest due to its superior properties inthermal conductivity, electron transport, and light emission. GaN-based materialshave potential applications in optoelectronic devices because of their attractivephysical properties.One-dimensional GaN nanostructure has potential applications inthe fields of full-color panel displays and nanometer electronic devices with highelectron migration rate. However, growth of GaN nanostructures with high crystallinequality is the pre-condition for the fabrication of GaN-based components.Until recently, GaN nanostructures usually be fabricated on sapphire substrates.However, sapphire itself is very expensive, insulated and hard to incise, low thermalconductivity as well as difficult techniques and high cost for devices. So, it isdisadvantageous to fabricate high power electronics devices. But the Si substrates canmake up sapphire’s shortcoming. Therefore, the investigation of GaN epitaxy onsilicon is of extreme practical importance. Although the direct epitaxial growth ofhexagonal GaN materials on Si substrates is very difficult owing to the large latticemismatch and the thermal expansion coefficient, Si is very attractive because of itsconsiderable advantages: high quality, relatively low cost, doping capability,availability of large and high-quality wafers, thermal and electrical conductivity, andpotential integration on Si technology. It has become a strong competitor for sapphire.There are many methods which have been reported on the fabrication of GaNnanostructures to date, such as Metal-organic Chemical Vapor DePosition )MOCVD),Molecular Beam Epitaxy )MBE), Hydride Vapor Phase Epitaxy )HVPE), and so on.Among them, MOCVD is most commonly used. In this paper, i.e., through theaddition of the inert additives )CaF₂) in a low melting-point metal, Ga, the large-scale1D GaN nanowires with high crystalline quality were successfully fabricated onSi)111) substrates coated with NiCl₂as catalyst by chemical vapor deposition )CVD)method. The microstructure, composition, morphology and photoluminescence )PL) light emitting properties of the GaN nanowires were analysed in detail.The result indicated that, the use of inert additives )CaF₂) was effective to reducethe temperature during the acting. And under different conditions, there are differentmorphologies and qualities of GaN nanostrctures grown on the substrates. Under thebest condition of process parameters, the GaN nanowires are mainly wurtzitestructures, and having the size of 20-50 nm in diameter and several tens of microns inlength with some nano-droplets on their tips, which reveals that the growthmechanism of GaN nanowires agrees with vapor-liquid-solid )VLS) process.Monoclinicβ-Ga₂O₃with a wide band gap of 4.9 eV is capable to be applied as atransparent conducting oxide material in the next generation optoelectronic devices,and recently,β-Ga₂O₃has become a promising candidate for new optoelectronicnanodevices tunable from ultraviolet to red light, because conventional transparentconductive oxides are constricted to the visible wavelength region, therefore,considerable efforts have been directed towards the synthesis ofβ-Ga₂O₃nanomaterials by various techniques such as arc discharge of GaN powders, physicalevaporation, laser ablation, metal organic chemical vapor deposition )MOCVD), andball milled method. However, these methods need complicated equipments, highdemand for experimental conditions like high vacuum, or induct heteroatoms. In thispaper, we have introduced a novel, simple, and convenient chemical vapordeposition )CVD) method to synthesize theβ-Ga₂O₃nanorod clumps, which werefabricated on Si )111) substrates coated with NiCl2as catalyst. A simple method, but asplendid result, that is which we want to point out specially. The microstructure,composition, morphology and photoluminescence )PL) light emitting property of theβ-Ga₂O₃nanorod clumps were also analyzed in detail.The compositions, microstructures, morphologies and light emitting properties ofnanostructures grown on the substrates were characterized by X-raydiffraction )XRD), FT-IR spectrophotometer )FTIR), scanning electronmicroscope )SEM), high-resolution transmission electron microscope )HRTEM),Raman spectroscopy and photoluminescence )PL).