Fig. 3
From: Fabrication and Optical Properties of Strain-free Self-assembled Mesoscopic GaAs Structures
a Two top view schematic outlines of the initial hole-mound structure of GaAs surface (left diagram) and after covering with a 20-nm Al0.33Ga0.67As layer (right). The third diagram is the top view of the MGS covered with a 20-nm top Al0.33Ga0.67As layer and 5-nm GaAs, indicating two possible regions where the optical emissions occur. The dotted lines show the position where the structure was cut for HAADF-STEM analysis. b Illustration of the cross-section view of the structure. c HAADF-STEM image (false color scale to enhance contrast) of a sample with 5-nm GaAs in the [110] direction. We can identify the Al0.33Ga0.67As barriers by their different material contrast as well as the mesoscopic structure by the increasing thickness of the GaAs layer between the AlGaAs barriers. d HAADF-STEM cross-section image of a sample with 5-nm GaAs in the [1–10] direction. The cut is not exactly in the middle as indicated in (a). We can observe the initial hole and its mound structure