It was noted that the impetus for dislocation motion in thin films was generally understood in terms of Peach-Koehler forces. However, in the case of III-nitride films grown onto step-free 4H-SiC mesas, it was instead the gradient of the strain energy arising from the mesa-edge that was implicated in driving misfit dislocations. Using the strain-profile as a function of the distance from the mesa-edge, and the line tension of the c-plane threading arms, calculations were made of the excess stress which drove the half-loop from the mesa-edge and into the mesa interior. The half-loop excess stress was compared with the excess stress driving the tilt of threading edge-dislocations, which was proposed to be one of the principal strain-relief mechanisms in III-nitride films. The excess stress which drove c-plane half-loops ranged from a few 1000MPa, at the mesa-edge, to a few 100MPa towards the mesa interior. The excess stress which drove the tilt of threading edge dislocations exceeded 20000MPa. However, the greater excess stress which drove dislocation tilt did not dominate the strain-relief of III-nitride films on step-free SiC mesas, due to the difficulty of nucleation of threading dislocations in the absence of interfacial steps.

Strain Relief and Dislocation Motion in III-Nitride Films Grown on Stepped and Step-Free 4H-SiC Mesas. M.E.Twigg, N.D.Bassim, M.A.Mastro, C.R.Eddy, R.L.Henry, J.C.Culbertson, R.T.Holm, P.Neudeck, J.A.Powell, A.J.Trunek: Journal of Applied Physics, 2007, 101[5], 053509 (6pp)