Reduction of threading dislocations in AlGaN layers grown on AlN/sapphire templates using high-temperature GaN interlayer

Crack-free AlGaN layers were grown on AlN/sapphire templates by low-pressure metalorganic chemical vapor deposition. Reduction of threading-dislocation (TD) density is achieved by inserting a high-temperature GaN interlayer between the AlGaN and AlN layers. Structural characterization reveals that such an interlayer can efficiently block the TDs propagating from the underlying AlN layer, and reduce the TD density in the subsequent AlGaN layer by one order of magnitude with an optimum thickness of 25 nm. It is also clarified that the decrease of edge TDs is the dominant contribution to this reduction.