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

摘要

Using in situ wafer-curvature measurements of thin-film stress, we determine the critical thickness for strain relaxation in Al_(x)Ga_(1-x)N/GaN heterostructures with 0.14≤x≤1. 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.