Fabrication And Photoelectric Properties Of GaN/ZnO（Cu₂O） Nanowire Heterojunctions

Gallium nitride （GaN） is a direct band gap semiconductor material having a wide band gap （3.4eV）, known as the third generation of semiconductor materials with superior thermal stability, chemical andoptical properties, following the first generation of the Ge, Si semiconductor materials andsecond-generation of GaAs, InP compound semiconductor materials. Because of its high power at highfrequency microwave devices and components, especially blue, short-wave ultraviolet light and otheroptoelectronic devices with attractive prospects, preparing GaN nanomaterials has aroused great interestand attention, has become the global the frontier and hot of nanotechnology field. Zinc oxide （ZnO） withbroad application prospects is a versatile group II-VI oxide semiconductor material with a direct band gapwide bandgap （3.37eV） and exciton binding energy of60meV at room temperature which has a highlyefficient exciton emission in semiconductor lasers, solar cells and light-emitting diodes and other areas. Inthis paper, based on the GaN and ZnO nanomaterials for applications in light-emitting diodes wesuccessfully prepared GaN-based and ZnO-based nanowire heterostructures, and their opticalcharacteristics have been investigated. The main work is as follows:1. n-GaN/p-Cu2O heterojunctions have been successfully prepared using a simple method ofphysical vapor deposition （PVD）: Si （111）, diamond （111） and Cu2O （111） were used as three kinds ofsubstrates for depositing GaN nanowire arrays epitaxially via PVD techniques. The morphology, structureand chemical composition of the samples were characterized and analyzed by scanning electron microscopy,high-resolution transmission electron microscopy, selected area electron diffraction and energy dispersivespectroscopy. The experimental results show that these nanowires with wurtzite structure almost areperpendicular to the bottom surface, because of the （₁100）-plane GaN nanowires and （111） planes of Cu2Ohas a good degree of lattice matching. In addition, UV luminescence spectroscopy （UVPL） show that theemission intensity of GaN/Cu2O heterojunction is stronger than previously reported GaN/Si andGaN/Diamond, showing GaN/Cu2O heterojunction excellent luminescent properties. These results indicatethat: GaN/Cu2O heterojunction preparation has potential applications in the production of electrical partsultraviolet aspects.2. Single n-ZnO/p-GaN nanowire heterostructures have been prepared successfully on the silicon（010） using a chemical vapor deposition （CVD） process. Based on CVD technique the Si substrate, ananowire arrays were grown firstly, and then n-ZnO nanowires continuely were depositd on the top ofp-AlGaN. High-resolution transmission electron microscopy and selected area electron diffraction showedthat n-ZnO nanowires grown well on the top surface of the p-AlGaN nanowires and both of them weretested with wurtzite structures. First, I-V curves of single heterostructure nanowire were tested via Au/Tielectrode and the results show that the rectifier characteristics in nanowire heterostructure is similar to thatof diode, and both Au/Ti/n-ZnO and Au/Ti/p-AlGaN showed good ohmic characteristics. Secondly, on theroom-temperature ultraviolet electroluminescent tests of single heterojunction nanowires was found that asthe current increases, its emission intensity increases first and then decreases, when current is4μA the luminous intensity is strongest of all. Finally, the carrier recombination luminescence mechanism isexplained using the n-ZnO/p-GaN LED’s PN junction band model and possibility of above phenomenonwas discussed. The study based on a single nanowire heterostructures offer the possibility of newapplications for the area of nanoscale light-emitting devices and light sources.