The Puzzle of Exciton Localisation in GaN-Based Structures: TEM, AFM and 3D APFIM Hold the Key

Abstract

The InGaN/GaN quantum well system emits intense light even though the dislocation density is high. This is a puzzle since dislocations should quench the light emission. Photoluminescence (PL) experiments show that the excitons in the InGaN quantum well are localised on a nanometre scale, thus separating the carriers from most of the dislocations. Many papers report transmission electron microscopy (TEM) results showing that this localisation is caused by gross indium clustering in the InGaN quantum wells, but our TEM reveals no gross indium clustering. Three-dimensional atom probe field ion microscopy confirms that InGaN is a random alloy. Mechanisms are given for localisation on a nm scale. Confinement oil a broader length scale (50 - 100 nm) can also occur in some InGaN quantum wells.