In situ measurements of the critical thickness for strain relaxation in AlGaN/GaN heterostructures

Using in situ wafer-curvature measurements of thin-film stress, we determine the critical thickness for strain relaxation in AlxGa1-xN/GaN heterostructures with 0.14less than or equal toxless than or equal to1. The surface morphology of selected films is examined by atomic force microscopy. Comparison of these measurements with critical-thickness models for brittle fracture and dislocation glide suggests that the onset of strain relaxation occurs by surface fracture for all compositions. Misfit-dislocations follow initial fracture, with slip-system selection occurring under the influence of composition-dependent changes in surface morphology. (C) 2004 American Institute of Physics.