Study On Optical And Electrical Performance Of Doping Regulated GaN Nanowires

Gallium nitride(Ga N)is a semiconductor material with direct wide bandgap.It is considered as a typical example of the third generation semiconductor due to the excellent properties,such as high electron mobility,good heat resistance,excellent corrosion resistance and excellent radiation resistance.Ga N nanowires possess the advantages of small size effect and quantum effect.By doping elements in Ga N nanowires,the field effect transistors,LED luminescent materials,sensing materials and high-frequency electronic devices are widely used.This article studyed the catalytic growth and the growth without any catalytic preparation of Mg doping Ga N nanowires,which were fabricated by microwave plasma chemical vapor deposition(MPCVD)system.The ammonia-free preparation process was selected and regulated the parameters of growth process to explore the transformation law of morphology and structure.Furthermore,the nucleation and photoelectric properties of nanowires were studyed.The main research progresses are as follows:1.Mg doped Ga N nanowires were grown on Si(100)substrates by a MPCVD system.Precursor powders were composed of carbon powder,Ga₂O₃ powder and Mg O powder.The substrates were sputtered Au film as catalyst and the crucible was selected as graphite which had remarkable thermal conductivity and reducibility.Mg doping Ga N nanowires with square cross section morphology and a diameter ranging from 300to 400 nm.Through regulating the Mg O investment proportion of precursor powders,the cross section morphology of nanowires could control from triangle into quadrilateral.The growth temperature mainly effects on the diameters of nanowires.With the growth temperature increased,the diameters of nanowires showed a trend of increasing initially and decreasing afterwards.The optimal atmosphere for nanowires growth should be maintained with N₂ flow rate of 13 sccm and pressure of 10 Torr.Prolonged reaction time will lead to a side wall thickening of the nanowires.A model of nanowires nucleation and growth from vapor-liquid-solid(VLS)process to vapor-solid(VS)process was proposed.2.On the basis of the above experiments,Mg doped Ga N nanowires with uniform morphology and large area growth were prepared on the graphite substrate without catalyst.The nanowires had preferable crystallinity when the growth temperature was maintained at 900?and the microwave power was 400 W.The nucleation process of nanowires was less than 10min.Increasing N₂ flow rate could improve the diameters and lengths of the nanowires.Controlling the microwave power could adjust the morphology and density of the nanowires.The mechanism of controlling the nucleation growth of Ga N nanowires based on non-catalytic Mg doping was further studied.Mg doping reduced the nucleation energy of Ga N nanowires and increased the number of nucleation in per unit area.Mg doping increases the size of Ga N nucleation and maintained a spherical crown morphology which resulted in increasing of nanowires diameters.3.The field emission performance of Mg doped Ga N nanowires prepared by Au catalysis was analyzed.The results shown that Mg doped could improve the field emission performance of Ga N nanowires,which decreased the turn-on volage as low as 5.4 V/?m and kept high current density.The field emission performance of Mg doped Ga N nanowires grown without catalyst could also reach 5.6 V/?m,but most of them performed worse than Au catalyzed nanowires in field emission performance.Mg doping leads to the occurrence of doping levels in Ga N and promoted the red shift of the luminous peak in the PL spectrum from 360 nm to 380 nm.More deep levels were generated during the doping process.