Investigation Of Synthesizing Of GaN Films And One-dimensional Nanostructures With Pd Buffer Layer

Nano-materials and nano-technology is a new subject rising rapidly in the late 1980s and the research object is with the material or structure whose sizes ranging from 1 to 100nm. Scientists predict that the nano science and technology will absolutely be dominant in all scientific fields in the 21st century, nanomaterial is the foundation of the application of nanotechnology, nanomaterials have received steadily groing interests as a rusult of not only their particular and facscinating properties,but also their potential application in many fields. As the typical representative of the third generation of semiconductor materials, GaN has attracted more and more researchers because of their excellent properties and application value.GaN is an excellentⅢ-Ⅴwide-band gap semiconductor material, whse energy gap is 3.4eV at room temperature.with high luminescent efficiency, high thermal conductance efficiency, and can endure high temperature, radiation, and acid and alkali, high intensity and high rigidity. Because light emission from infrared light to ultraviolet light and the full color panel display of red, yellow, and blue light can be actualized, GaN has been considered as an ideal material for the fabrication of blue/green light emitting diodes (LDS), laser diodes (LDS) and high power integrated. After 1990, the realization of some pivotally technieal methods and the development of materials growth and devices technics made GaN to be the research focus of the world. So far, GaN materials have been synthesized by many different techniques such as carbon nanotube rate-limiting reaction,chemical vapor deposition,arc discharge method,metal-catalyzed growth.In this paper, one-dimensional GaN nanostructures are synthesized by ammoniating the Ga2O3/Pd films on Si substrates and Sapphire substrates by radio frequency magnetron sputtering system. The structure, composition, morphology, optical properties of the as-prepared nanostructures are studied thoroughly. The growth mechanism of GaN nanostructures is explored. The properties of the buffer layer and its effect on GaN nanostructures are also studied. All the results are as follows:1. Synthesis of one-dimensional GaN nanostructures through magnetron sputtering and ammonification methodMetal Pd is used as the buffer layer; Pd films are deposited on Si substrates and Sapphire substrates by radio frequency magnetron sputtering system. Then thick Ga2O3 films (about 500nm) are sputtered on Pd layer by JCK-500A magnetron sputtering system. The results reveal that different anneal temperature and different ammoniating time of Ga2O3/Pd films and different thickness of Pd layer have a great influence on the synthesis of GaN nanostructures. The synthesized nanostructures are of hexagonal wurtzite single-crystal GaN, showing their morphologies as long and straight nanowires, bambooleaves nanorods, and nano-clusters nanostructures.2. Analysis of the morphology, structure, composition and optical properties of the GaN nanostructuresThe surface morphology, lattice structure were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED). The spacestructure and composition of the products are analyzed by X-ray diffraction (XRD), energy diffuse X-ray spectrometer (EDX) and X-ray photoelectron spectroscopy (XPS). In addition, The infrared absorption and scattering characteristics are analyzed by fourier transform infrared spectroscopy (FTIR) and laman spectrophotometer (Laman), and the room temperature photoluminescence (PL) spectrum of the products was measured with fluorescence spectrophotometer.3. Exploration of the growth mechanism for GaN nanostructuresAlthough the melting point (1554℃) of bulk metal Pd is higher than the reaction temperature we used, the melting point of nanoparticles is lower than the corresponding bulk materials. The metal droplet with nano size has already formed and distributed on the surface of substrates at the ammoniation temperature, Which produce a lot of defects far more than before and their energy changed the energy distribution of the substrate surface. The broken keys of defects adsorp free gaseous Ga atoms and N atoms and form Ga-Pd-N structures. Adsorption and broken key emerging continue, adsorption is ongoing. At the same time, NH3 decomposes step by step to NH2, NH, H2 and N at high ammoniating temperature. Ga2O3 particles are reduced to gaseous Ga2O by H2 and then GaN molecules are synthesized through the reaction of Ga2O and ammonia. Ga2O and NH3 gases evaporate and travel to the substrate, where the catalytic reaction takes place. The formed GaN molecules deposited on the substrate and agglomerate into GaN crystalline nuclei. When all microcrystallines grow along the same direction, it will form different GaN nanostructrues, Such as nanowires, nanotubes,and nano particles. Nanodroplets are found at the tips of many nanostructures; the growth process follows probably VLS mechanism. We also deposited the Ga2O3 film directly onto Si substrates with the same condition, but no nanostructures were formed. Consequently, we believe that Pd probably acts as the nucleation sites for GaN embryos and plays the role of catalyst in the reaction, as nanostructures tend not to grow without it.