Raman spectroscopy was used to analyse strain in films which had been grown onto sapphire substrates by means of NH3-source molecular beam epitaxy. In some cases, films which were grown on c-face sapphire substrates exhibited high tensile biaxial strains as well as the expected compressive biaxial strain. This anomalous behaviour could be explained in terms of an interstitial H-dependent lattice dilation. The H concentration in the films was measured by means of nuclear reaction analysis. With increasing H incorporation, the residual compressive biaxial strain first relaxed further, and then turned into a tensile strain when the H content exceeded a critical concentration. The H incorporation during growth was growth-rate dependent, and was supposed to be strain-driven. It was suggested that strain-induced interstitial incorporation was another means by which strain relaxation during hetero-epitaxy could occur, in addition to the well-known mechanisms of dislocation formation and growth-front roughening.

Hydrogen-Dependent Lattice Dilation in GaN J.P.Zhang, X.L.Wang, D.Z.Sun, M.Y.Kong: Semiconductor Science and Technology, 2000, 15[6], 619-21