The Preparation And First-principle Study Of AlN Coating GaN Nanowire Composite Structure

Gallium nitride(GaN)is a direct band gap semiconducting material that has excellent performance,such as wide band gap,small work function,high thermal conductivity,stable physical and chemical properties,and higher melting point(1500 ?),which makes it a typical cathode material for field emission in the III-V family.Aluminum nitride(AlN)is similar to GaN,which is also a kind of direct wide band gap semiconductor materials in the III-V family.The band gap of AIN is larger than GaN,the work function of AIN is smaller than GaN,and it has good compatibility with semiconductor interface.In addition,the structures of AlN and GaN are wurtzite,they have similar lattice matching and thermal expansion coefficient,these make it become the preferred material for coating GaN.So,this article studied and prepared AIN coating GaN nanowire composite structure from theory and experiment.Theoretically,density functional theory(DFT)was performed to analyze the electronic structures(including energy band,density of states and local charge distribution)and work functions of AIN coating GaN nanowire composite structures.The results showed that AIN coating GaN nanowire composite structures were very stable;The band gaps of AIN coating GaN nanowire composite structures were still direct band gap compared with GaN,and they were greater than the band gap of GaN;A large amount of local charge was introduced into the bottom of the conduction band because of AIN,the high local charge increased the electron density of the conduction band,thereby,the density of the electron emission was increased;In addition,the work functions of AIN coating GaN nanowire composite structure had been reduced because of AIN.So,the field emission properties of the AIN coating GaN nanowire composite structure could be improved.Experimently,we have synthesized and characterized successfully AIN coating GaN nanowire composite structures via the chemical vapor deposition(CVD)on Pt-coated Si(111)substrates based on the vapor-liquid-solid(V-L-S)and vapor-solid(V-S)growth mechanisms,respectively.Firstly,we studied the effect of temperature on the AIN coating GaN nanowire composite structures,the results showed that the optimal temperature for preparing AIN coating GaN nanowire composite structures was 750 ?.Secondly,we studied the effect of density of GaN nanowires on the AIN coating GaN nanowire composite structures,the results showed that dense and sparse density of GaN nanowire were bad for preparing AIN coating GaN nanowire composite structures.Finally,the morphology and the crystal structure of AIN coating GaN nanowire composite structures were characterized by scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),and X-ray diffraction(XRD):EDS showed that the atomic percentage content of GaN nanowire core and AIN shell were 65%and 35%;XRD showed that the structures of GaN core and AIN shell were hexagonal.