Ellipsoidal InAs quantum dots observed by cross-sectional scanning tunneling microscopy

We report a detailed analysis of the shape, size, and composition of self-assembled InAs quantum dots based on cross-sectional scanning tunneling microscopy (X-STM) experiments. X-STM measurements on 13 individual quantum dots reveal an ellipsoidal dot shape with an average height of 8 nm and a diameter of 26 nm. Analysis of the outward relaxation and lattice constant profiles shows that the dots consist of an InGaAs alloy with a profound gradient in the indium concentration in both horizontal and vertical directions. These results are important to obtain a deeper understanding of the relationship between the structural and electronic properties of semiconductor quantum dots.