Preparation,Field Emission Properties And First-principles Calculation Of Al Doped,Al/N Co-doped SiC Nanowires

SiC nanowires are representative third generation semiconductor materials.In addition to the high melting point,high hardness,good thermal stability,mechanical properties and excellent high temperature properties of SiC,SiC nanowires can also be used in extreme environments such as high temperature,high frequency,high power and radiation resistance.Due to these excellent properties,SiC nanowires also occupy irreplaceable positions in the field of field emission cathode materials.However,the field emission properties of intrinsic SiC nanowires can not meet the needs of their use as field emission cathode materials.Therefore,in order to improve the field emission performance of SiC nanowires,the study on Al doping and Al/N co-doping in SiC nanowires were carried out to obtain Al-doped SiC nanowires and Al/N co-doped SiC nanowires with excellent field emission properties,which will make the SiC nanowires being able to meet the field emission requirements for cathode materials.The mechanism of increased field emission performance by Al or Al/N co-doping is systematically and deeply studied by first principle calculation.The main contents of the study are as follows:（1）In situ Al doped SiC nanowires were prepared using PCS as Si source and C source,Si powder as auxiliary Si source,aluminum nitrate as Al source and nickel nitrate as catalyst by one step CVD method.The effects of reaction temperature,ratio of raw materials and heat prevention time on the morphology and field emission properties of in situ Al-doped SiC nanowires were studied.SEM and TEM and other method were employed to characterize the product.The results show that the optimum preparation parameters of Al-doped SiC nanowires are as follows:reaction temperature1400℃,heat prevention time 60min,mass ratio of raw material 1:0.03.The distribution of nanowires is uniform and the diameter of nanowires is also uniform.The material exhibits excellent field emission performance,and its turn-on field and threshold field are 0.9V·μm^-1and 3.1 V·μm^-1,respectively.（2）Al/N co-doped SiC nanowires were prepared,using NH₃ gas as nitrogen source.The effects of nitriding temperature and nitriding time on the field emission properties of the prepared Al/N co-doped SiC nanowires were studied.The optimum preparation parameters of Al/N co-doped SiC nanowires are as follows:nitriding temperature 900℃,nitriding time 180min.The products were characterized by SEM XPS,and it was confirmed that the morphology of the products did not change obviously after N doping,and the N atom replaced the C atom into the SiC lattice.Compared with Al-doped SiC nanowires before nitriding,the field emission properties of nitrided products were further improved with a turn on field of 0.4 V·μm^-1 and threshold field of 1.9 V·μm^-1,respectively.（3）In situ Al/N co-doped SiC nanowires were prepared via one step CVD method using PCS as Si source and C source,Si powder as auxiliary Si source,aluminum nitrate as Al source,melamine as N source and nickel nitrate as catalyst.The effects of reaction temperature,ratio of raw materials and heat prevention time on the morphology and field emission properties of Al/N co-doped SiC nanowires were studied.SEM and XPS were employed to characterization product.The results show that the optimum preparation parameters of Al-doped SiC nanowires are as follows:ratio of raw materials（PCS:melamine）1:2;reaction temperature 1350℃;heat preservation time 90min.The product exhibits good field emission performance,and its turn-on field and threshold field are 0.7 V·μm^-1and 3.2 V·μm^-1,respectively.（4）The band gap and density of states of Al and Al/N co-doped SiC were studied by first-principle calculation.The influence of Al and Al/N doping on the band gap of SiC was summarized.This paper analyzes the internal causes of the field emission properties of SiC enhanced by Al/N co-doping,and probes into the mechanism of the enhancement of field emission properties of SiC by Al/N co-doping.