Control and elimination of cracking of AlGaN using low-temperature AlGaN interlayers

Abstract

We demonstrate that the insertion of low-temperature AlGaN interlayers is effective in reducing mismatch-induced tensile stress and suppressing the formation of cracks during growth of high-temperature AlGaN directly upon GaN epilayers. Stress evolution and relaxation is monitored using an in situ optical stress sensor. The combination of in situ and ex situ characterization techniques enables us to determine the degree of pseudomorphism in the interlayers. It is observed that the elastic tensile mismatch between AlGaN and GaN is mediated by the relaxation of interlayers; the use of interlayers offers tunability in the in-plane lattice parameters.