ABSTRACT
The optoelectronic properties of quantum dot (QD) devices are influenced essentially by the size, shape, crystal morphology, chemical composition and strain of the QDs. During the capping process the strain, of necessity, changes because of the different atomic sizes of the species in the QD and the capping layer. The capping process also changes the QD shape and composition. In the present study, single layer InAs/GaAs (001) QD structures with different GaAs capping layer thicknesses have been fabricated by MBE growth. The different techniques of transmission electron microscopy (TEM), including diffraction-contrast and high-resolution lattice imaging (HRTEM) as well as analytical electron microscopy (AEM), have been used to characterise both the microstructure and microchemistry down to the atomic scale. The atomic scale details obtained by HRTEM are combined with the results of field-emission gun scanning transmission electron microscopy (FEG-STEM) to provide information on the structure and composition change of the QDs during their encapsulation by GaAs.
