Study Of Enhancement Of Field Emission Properties Of GaN Nanowires

Gallium nitride(GaN)is a wide band gap(3.4 e V)semiconducting material that has excellent performance,such as optical properties,electrical properties,good thermal stability and mechanical properties.So that GaN has wide range of applications in optoelectronic and microelectronic devices.GaN semiconductor material,which has small electron affinity(2.7-3.3e V),physical and chemical stablity,and higher melting point(1500oC),is a promising cathode material for field emission.GaN NWs have excellent performance of field emission properties as a kind of one-dimensional nano-materials which has high aspect ratio,applying widely in emission devices.The field emission properties of GaN NWs not only related to ratio of length to diameter of the outside,but also related to morphology and doping factors.This research summarized the enhancement of field emission properties of GaN NWs from two aspects such as morphology and doping atoms,the main content shows as follows:1.Special morphologies of GaN NWs have been synthesized.The FE enhancement factor of GaN NWs is improved,which enhance the field emission properties of GaN NWs.Tower-like GaN NWs,grown on Pt/Si(111)substrate,have been synthesized using CVD method.The tower-like GaN NWs possess hexagonal-shaped cross-sections.Crystal structure of tower-like GaN nanowires is hexagonal wurtzite structure.Tower-like GaN NW's preferential growth direction is along[0001]direction.Tower-like GaN NWs have a low turn-on field of 4.39 V/?m and larger FE enhancement factor of 2087.Pencil-like GaN NWs have been synthesized on Pt/Si(111)substrate via CVD method.The diameter of pencil-like GaN NWs decreases gradually from?600 nm to?200 nm along the wire axis,and the length of pencil-like GaN NWs extend to ten micrometers.Crystal structure of pencil-like GaN NWs is hexagonal wurtzite structure.Pencil-like GaN NWs have a low turn-on field of 3.5 V/?m and high field emission current stability.The turn-on field of tower-like GaN NWs and pencil-like GaN NWs are lower than ordinary GaN NWs,showing that the field emission properties have been enhanced because of special morphologies.Three-dimensional branch GaN NWs have been synthesized on Pt/Si(111)substrate in two steps by CVD method.The first step is the preparation of one-dimensional GaN NWs on Si substrate,and the second step is continue to grow branched structure of GaN NWs after sputtering Pt film on the first step preparation of one-dimensional GaN NWs.Three-dimensional branch GaN NWs are wurtzite hexagonal structure.The diameter of middle GaN NWs is about 200 nm.The diameter of branch GaN NWs is about 70 nm,and the length of branch GaN NWs is about 500 nm.Three-dimensional branch GaN NWs has six branch structures,and an angle of branch structures is about 60�.Three-dimensional branch GaN NWs has a low turn-on field of 2.35 V/?m.The FE enhancement factor is about 2938,and the maximum current density is 1787?A/cm~2.The FE enhancement factor and the maximum current density of three-dimensional branch GaN NWs are far greater than ordinary GaN NWs,and the turn-on field of three-dimensional branch GaN NWs is much lower than ordinary GaN NWs,showing that the field emission properties of three-dimensional branch GaN NWs has an excellent performance compared with ordinary GaN NWs.2.Se-doped GaN NWs have been synthesized.The work function of GaN NWs is reduced,which enhance the field emission properties of GaN NWs.The electronic structures and work functions of Se-doped GaN NWs have been investigated using density functional theory(DFT).There are three kinds of doping model(doping concentrations are 2.08%,4.17%and 6.25%)and pure model.The calculation results show that,compared with the pure GaN NWs,the Se-doped GaN NWs'Fermi level is upshift than pure GaN NWs,and the donor states near Fermi level are mainly formed through the hybridization between Se 4p and N 2p states.The work functions of three kinds of Se-doped GaN NWs are small than pure GaN NWs,so we can reduce the work function to enhance the field emission properties of GaN NWs by doping Se atoms.Se-doped GaN NWs with different concentrations(1.61%,4.02%,5.98%)have been synthesized on Pt/Si(111)substrates by CVD method.The turn on field of three kinds of Se-doped GaN NWs are lower than pure GaN NWs,and field emission properties of Se-doped GaN NWs are better than pure GaN NWs,showing same results with theoretical research.