Misfitstrain and growth characteristics of InAs/GaAs quantum dots Grown by molecular beam epitaxy

Self-assembled InAs/GaAs quantum dots (QDs) were grown by molecular-beam epitaxy and their structure and strain characteristics were studied by using transmission electron microscopy (TEM). TEM investigations were performed by conventional bright field TEM, high-resolution electron microscopy (HREM), annular dark field (ADF) and high angle annular dark field(HAADF)-STEM techniques. In addition, strain analysis was performed on an atomic-length scale by measuring the space of lattices in HREM. Compressive strain was induced to uncapped QDs from GaAs substrate and the strain increased more than 3.5 % after GaAs cap layer growth. On the other hand, tensile strain by capped QDs was induced to GaAs up to 10 nm over the QDs, i.e. 15 nm over the wetting layer. It was also confirmed that the tensile strain extension resulted in aligned QD growth with 15 nm thick spacers