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

We demonstrate that the insertion of low-temperature AlGaN interlayers is e ffective in reducing mismatch-induced tensile stress and suppressing the fo rmation of cracks during growth of high-temperature AlGaN directly upon GaN epilayers. Stress evolution and relaxation is monitored using an in situ o ptical stress sensor. The combination of in situ and ex situ characterizati on techniques enables us to determine the degree of pseudomorphism in the i nterlayers. It is observed that the elastic tensile mismatch between AlGaN and GaN is mediated by the relaxation of interlayers; the use of interlayer s offers tunability in the in-plane lattice parameters. (C) 2001 American I nstitute of Physics.