Brittle-ductile relaxation kinetics of strained AlGaN/GaN heterostructures

We have directly measured the stress evolution during metal-organic chemica l vapor deposition of AlGaN/GaN heterostructures on sapphire. In situ stres s measurements were correlated with ex situ microstructural analysis to det ermine directly a critical thickness for cracking and the subsequent relaxa tion kinetics of tensile-strained AlxGa1-xN grown on GaN. Cracks appear to initiate the formation of misfit dislocations at the AlGaN/GaN interface, w hich account for the majority of the strain relaxation. (C) 2000 American I nstitute of Physics. [S0003-6951(00)01212-2].