Microstructural and compositional analyses of GaN‐based nanostructures

Abstract

AbstractComposition and microstructure of GaN‐based island structures and distributed Bragg reflectors (DBRs) were investigated with transmission electron microscopy (TEM). We analysed free‐standing InGaN islands and islands capped with GaN. Growth of the islands performed by molecular beam epitaxy (MBE) and metal organic vapour phase epitaxy (MOVPE) resulted in different microstructures. The islands grown by MBE were plastically relaxed. Cap layer deposition resulted in a rapid dissolution of the islands already at early stages of cap layer growth. These findings are confirmed by grazing‐incidence X‐ray diffraction (GIXRD). In contrast, the islands grown by MOVPE relax only elastically.Strain state analysis (SSA) revealed that the indium concentration increases towards the tips of the islands. For an application as quantum dots, the islands must be embedded into DBRs. Structure and composition of AlyGa1–yN/GaN Bragg reflectors on top of an AlGaN buffer layer and InxAl1–xN/GaN Bragg reflectors on top of a GaN buffer layer were investigated. Specifically, structural defects such as threading dislocations (TDs) and inversion domains (IDs) were studied, and we investigated thicknesses, interfaces and interface roughnesses of the layers. As the peak reflectivities of the investigated DBRs do not reach the theoretical predictions, possible reasons are discussed.