The Controllable Dope And Surface Functionality Of Gallium Nitride Nanowires

Gallium nitride (GaN) has received a great deal of attention in the past decades because of its advantageous properties such as wide band-gap, high melting point, excellent thermal conductivity, large electron velocity, and chemical inertness. GaN can be operated at higher temperatures than conventional Si-based semiconductors and sensors. To date, the miniaturization of devices and the bottom-up synthetic technology have led to an increasing research interest in the fabrication of semiconductor nanostructures with various morphologies and diverse functions. Compared with their bulk counterparts, one-dimensional (1D) nanostructures may exhibit peculiar and unique properties because of their smaller size and large surface-to-volume ratio, as well as confined quantum effects.The presence of large amounts of nitrogen vacancies in gallium nitride material results in N-type GaN semiconductor. The doped gallium nitride by Molecular beam epitaxy and Metal-organic Chemical Vapor Deposition has been reported. But the equipment is expensive and the method process is complex. The horizontal tube furnace method has the advantage of simple process, easy operation and low cost. The radius of Zn atoms is very close to Ga’s, and the Zn doping will not cause deformation of the crystal structure of gallium nitride. GaN nanowires are used for the light emitting device. Wurtzite GaN nanostructures exhibit high piezoelectric properties and high spatial separation of charge carriers. These important characteristics open up the possibility of using GaN nanowires as building blocks for detector. In this thesis, we use the horizontal tube furnace to synthetic GaN nanowires under different experimental conditions. We choose zinc as a dopant for GaN nanowires and control the quantity of zinc by tuning the growth temperature. Anodic stripping voltammetry (ASV) is an effective approach in monitoring heavymetal ions in the environment. GaN nanowires serve as the working electrode to study the relationship between current intensity and silver ions concentration.(1) The morphology of wurtzite GaN nanostructures can be controlled by changing the NH3flow rate during thermal reaction of Ga2O3and NH3. Scanning electron microscopy and transmission electron microscopy revealed both thin smooth and thick corrugated nanowires. The ratio of Ga and N play an important role in the morphology of GaN nanowire.(2) One-dimensional GaN nanorods with corrugated morphology have been synthesized on graphite substrate without the assistance of any metal catalyst through a feasible thermal evaporation process. The GaN nanorods are well-crystallized and exhibit a preferential orientation along the [0001] direction with Ga3+-terminated (1011) and N3--terminated (1011) as side facets, finally leading to the corrugated morphology surface. The stabilization of the electrostatic surface energy of{1011} polar surface in a wurtzite-type hexagonal structure plays a key role in the formation of GaN nanorods with corrugated morphology.(3) Zn-doped GaN nanowires were synthesized in a co-deposition CVD process and the effects of Zn doping on the morphology and microstructure of GaN nanowires were studied in details. The quality of Zn in GaN nanowires can be controlled by changing the temperature of ZnO zone during thermal reaction of Ga2O3and NH3.(4) The GaN nanowires and films serve as an environmental friendly alternative electrode material for ASV trace metal analysis. Low detection limits of200ppb and10ppb have been achieved in the model analyte systems containing Ag+for nanowires and films, respectively. There is a good linear relationship between current and silver ion concentration.