Comparative study of high and low temperature AlN interlayers and their roles in the properties of GaN epilayers prepared by means of metal organic chemical vapour deposition on (00•1) plane sapphire substrates was carried out by high resolution X-ray diffraction, photoluminescence and Raman spectroscopy. It was found that the crystalline quality of GaN epilayers was improved significantly by using the high temperature AlN interlayers, which prevent the threading dislocations from extending, especially for the edge type dislocation. The analysis results based on photoluminescence and Raman measurements demonstrated that there exists more compressive stress in GaN epilayers with high temperature AlN interlayers. The band edge emission energy increases from 3.423 to 3.438eV and the frequency of the Raman shift of E2(TO) moves from 571.3 to 572.9/cm when the temperature of AlN interlayers increases from 700C to 1050C. It was believed that the temperature of AlN interlayers effectively determines the size, the density and the coalescence rate of the islands, and the high temperature AlN interlayers provided large size and low density islands for GaN epilayer growth and the threading dislocations were bent and interactive easily. Due to the threading dislocation reduction in GaN epilayers with high temperature AlN interlayers, the strain relaxation reduced drastically, and thus the compressive stress in GaN epilayers with high temperature AlN interlayers was high compared with that in GaN epilayers with low temperature AlN interlayers.

Comparative Study of Different Properties of GaN Films Grown on (0001) Sapphire Using High and Low Temperature AlN Interlayers. J.S.Xue, Y.Hao, J.C.Zhang, J.Y.Ni: Chinese Physics B, 2010, 19[5], 057203