Atomic-scale strain field and In atom distribution in multiple quantum wells InGaN/GaN

Abstract

We present an atomic-scale structural and compositional analysis of ultrathin layers in multiple quantum well InGaN/GaN, by high-angle annular dark field (HAADF) scanning transmission electron microscopy (STEM). A high-quality HAADF STEM image processed by two-dimensional smoothing and deconvolution provides precise atomic-column positions and clear contrast, thereby allowing us to map the strain field and In atom distribution in successive GaN and InGaN layers. We conclude from these maps that there is a local fluctuation of In atoms in the InGaN layers and the In-rich regions, considered as quantum dots, cause large expansion only along the [0001] direction.