Growth of crack-free AlGaN film on high-temperature thin AlN interlayer

We report on successful fabrication of crack-free thick AlGaN layers by introducing a thin AlN interlayer at the high temperature of 1000-1100°C on a high quality GaN epitaxial layer. The Al_0.52Ga_0.48N films grown with the optimized AlN interlayer exhibited mirror-like surface morphology and were free of cracks up to the thickness of 3μm. X-ray analyses and cathodoluminescence spectra showed excellent structural and optical quality of the AlGaN materials. Si-doped n-type AlGaN films were also grown on the high-temperature AlN interlayer, and excellent n-type conductivity was achieved up to Al_0.38Ga_0.62N with the electron concentration of 2.0 × 10¹⁸cm^-3 and the mobility of 79 cm²/V s. Furthermore, from monochromatic cathodoluminescence images, we proposed that initial cracking of the AlN interlayer reduces the residual stress, thus preventing cracking in the AlGaN layer by generating misfit dislocations at AlGaN/AlN interface.