Strain Relaxation in an AlGaN/GaN Quantum Well System

Summary

AlGaN/GaN quantum well stacks have been grown in a series with 10.5nm Al_0.5Ga_0.5N barriers and 1.5nm, 2.5nm and 3.5nm GaN wells. These samples have been studied by weak beam dark field (WBDF) TEM. Threading dislocations form ‘staircases’ in the stack, generating a short misfit segment at the lower interface of each well. By imaging dislocations at different tilts and opposite values of the deviation parameter s, it is established that the misfit segments are pure edge type and relieve strain in the GaN layers. Two mechanisms are proposed for the formation of these ‘staircase’ structures by climb.