Mapping of multiple-quantum-well layers and structure of V defects in InGaN/GaN diodes

Abstract

Cathodoluminescence mapping reveals threading defects, frequently formed by the lattice misfit between GaN and sapphire substrate, as a dark contrast connected with changes in the energy state. Multiple quantum wells, 2.5 nm In0.25Ga0.75N and 13.9 nm GaN layers, are resolved in the secondary electron image as well as in the backscattered electron image. The backscattered electron image, providing compositional mapping without surface effects such as cleaved steps, reveals the presence of V defects and confirms the thin six-walled structure of the V defect with InGaN/GaN {1011̄} layers. These scanning electron microscopy observations can be performed after very simple specimen preparation, namely just cleaving the sapphire substrate with the epilayers.