Comparative study of different properties of GaN films grown on(0001) sapphire using high and low temperature AlN interlayers

Comparative study of high and low temperature AlNinterlayers and their roles in the properties of GaN epilayersprepared by means of metal organic chemical vapour deposition on(0001) plane sapphire substrates is carried out by high resolutionx-ray diffraction, photoluminescence and Raman spectroscopy. It isfound that the crystalline quality of GaN epilayers is improvedsignificantly by using the high temperature AlN interlayers, whichprevent the threading dislocations from extending, especially forthe edge type dislocation. The analysis results based onphotoluminescence and Raman measurements demonstrate that thereexist more compressive stress in GaN epilayers with high temperatureAlN interlayers. The band edge emission energy increases from3.423~eV to 3.438~eV and the frequency of Raman shift of $E_{2}$(TO) moves from 571.3~cm$^{ - 1}$ to 572.9~cm$^{ - 1}$ when thetemperature of AlN interlayers increases from 700~$^{circ}$C to1050~$^{circ}$C. It is believed that the temperature of AlNinterlayers effectively determines the size, the density and thecoalescence rate of the islands, and the high temperature AlNinterlayers provide large size and low density islands for GaNepilayer growth and the threading dislocations are bent andinteractive easily. Due to the threading dislocation reduction inGaN epilayers with high temperature AlN interlayers, the approachesof strain relaxation reduce drastically, and thus the compressivestress in GaN epilayers with high temperature AlN interlayers ishigh compared with that in GaN epilayers with low temperature AlNinterlayers.