Quantitative transmission electron microscopic investigations were made of the relaxation of wurtzite-type GaN which had been grown, by plasma-induced molecular beam epitaxy, onto Al2O3(00•1). Terminating {11•0}-substrate fringes at the interfaces were monitored, and the efficiency of the relaxation was measured. The in-plane orientation between GaN and substrate revealed a lattice misfit of -13.9%. Therefore, the critical thickness for dislocation formation was reached as soon as the first monolayer of GaN was grown. An expected interfacial relaxation process was sought by means of high-resolution transmission electron microscopy. This revealed misfit dislocations which were confined to the interface region. The results revealed the effectiveness of the observed relaxation process. A relaxation of -11.8% and a residual strain of -2.1% were measured, and it appeared that only the latter caused a dislocation density of some 1010/cm2 in the GaN epilayer.

Quantitative transmission electron microscopic investigation of relaxation by misfit dislocations S.Kaiser, H.Preis, W.Gebhardt, O.Ambacher, H.Angerer, M.Stutzmann, A.Rosenauer, D.Gerthsen: Japanese Journal of Applied Physics - 1, 1998, 37[1], 84-9