Electron Microscopy Characterization of a Graded AlN/GaN Multilayer Grown by Plasma-Assisted MBE

Abstract

Misfit relaxation and related defects in AlN/GaN epitaxial heterostructures were studied using an MBE-grown AlN/GaN multilayer with graded AlN thicknesses starting from 3 up to 100 nm. Transmission electron microscopy techniques were employed. Principally elastic behaviour was observed below 6 nm AlN thickness, with some roughness and undulations due to local destabilization of the growth front. Above 6 nm, there is introduction of misfit and a-type threading dislocations. The threading dislocations were frequently found to adopt inclined zig-zag line directions across the heterostructure, thus contributing to the relief of alternating compressive-tensile elastic strain.