Residual Strain Variations in MBE-Grown InN Thin Films

Abstract

The different nature of the residual strain in InN thin films, grown on GaN/Al2O3 templates, is investigated. Wurtzite InN grows epitaxially on GaN with a well-defined orientation relationship, having threading dislocations as the dominant structural defect. Electron microscopy, Raman and X-ray absorption fine structure experiments reveal that the epilayers are subject to biaxial residual strain, either compressive or tensile. The origin of compressive strain is due to the InN/GaN structural mismatch and thermal strains imposed from sapphire, whereas tensile strain is predominately attributed to InN island coalescence during the initial growth stages.