The Study Of MOCVD Growth Of GaN Materials Based On Magnetron Sputterred AlN

Recntly, the research of Gallium nitrid(Ga N) on Silicon(Si) has been widespread concerned. As a substrate, Si not only has good thermal conductivity and low cost, but also be compatible with conventional CMOS processes. Though the technology of the nuclear layer makes it possible for Ga N obtaining a high crystalline quality on a large lattice mismatch substrate. The nucleation layer growned by MOCVD still has a dependence on subtratre, resulting in a larger number of lattice mismatching, limiting the application field of Ga N. And magnetron sputtering is a thin-film technique that has very weak dependence on the substrate.If the epitaxial grows on Al N of the magnetron sputtering has a low defect density and a good surface morphology, one can growed Ga N epitaxial material on any kind of high-temperature materials. Before this article, there is little study of this technology by MOCVD regrowth. Therefore, the main purpose of this paper is to study the growth of Ga N on the sputtered Al N that based on sapphire substrates. The main work in this paper are as follows:(1) In order to remove O impurities at the interface of magnetron sputtered Al N, we use the method of removed impurities by MOCVD. By comparing different nitrogen time and ammonia nitrogen flow, we found that the removal of O impurities nitriding process needs to go through a longer period of time, and ammonia gas flow must be at a very high level to ensure that the chemical reaction has been to restore. Short nitridation time or low flow rate of ammonia can lead to insufficient nitride. High nitriding temperature can achieve good results and improve the crystal quality of Ga N by preferential etching of dislocations. But the high temperature damages the surface and more O impurities are adsorbed at the interface. It leads to the result of detteriorate the electrical characteristics.(2) In order to obtain a high crystalline quality and surface morphology of the Ga N material, different Ga N layer structures are studied. After insert a Ga N layer of low Ⅴ-Ⅲ ration,the lateral growth be enhanced. As a result, the screw dislocation density material bit greatly decreased from 2.81×108 cm-2 to 2.30×107 cm-2. By increass the thickness of Ga N layer, the screw dislocation density decreases from 2.81×108 cm-2 to 6.11×107cm-2, edge dislocation density decreases from 6.16×108 cm-2 to2.93×108 cm-2, and the surface of the root mean square roughness(RMS) reached 0.149 nm. By measuring Raman spectroscopy, we found that with the increase of Ga N thickness, the stress state of the material has entered a steady state.(3) In order to obtain Ga N materials with high resistance, we inserts a thin layer of Al N growed by MOCVD between the layer of Al N growed by magnetron sputtering and Ga N epitaxial layer to relax the mutation of two different materials and growth patterns. By changing the Ⅴ-Ⅲ ration of Al N, we obtains a Ga N material with high resistance reached 105Ω/□ and the crystalline quality of the material is also improved.(4) In order to study the growth mode of Al N, we design an experiment with diffferent thickness of Al N. By the measurements of XRD, AFM and others, we found that the growth of Al N epitaxial layer is not the traditional way that nucleates first and then merges.The growth mode is 2D coherent growth.In summary, with the study of Ga N materials based on magnetron sputterred Al N,we obtained high resistance materials with high crystalline quality and good surface morphology. The lowest Screw dislocation density is 1.01×107 cm-2, edge dislocation density is 2.93×108 cm-2, the minimum of surface RMS is 0.149 nm, Max-Min is 1.873 nm and the sheet resistance> 105Ω/□.