InAs quantum dot and wetting layer formation in GaAs and AlAs analyzed by cross-sectional scanning tunneling microscopy

Cross-sectional scanning-tunneling microscopy (X-STM) has been used to study the formation of self-assembled InAs quantum dots (QDs) and wetting layers on AlAs (100) and GaAs (100) surfaces. On AlAs we find a larger QD density and smaller QD size than for QDs grown on GaAs under the same growth conditions (500°C substrate temperature and 1.9 ML indium deposition). We have determined the indium composition of the QDs by fitting it to the measured outward relaxation of the cleaved surface using a three-dimensional finite element calculation based on elasticity theory. The QDs grown on GaAs show both a normal and a lateral gradient in the indium distribution whereas the QDs grown on AlAs show only a normal gradient. No significant differences in the segregated In-profiles for the wetting layers on GaAs and AlAs are observed. We suggest that the segregation of the wetting layer is mainly strain-driven, whereas the formation of the QDs is also determined by growth-kinetics.