Correlation between overgrowth morphology and optical properties of single self-assembled InP quantum dots

We have studied the early stages of GaInP overgrowth on InP quantum dots (QD’s) experimentally and theoretically. A direct correlation between the surface morphology and the optical properties of individual InP QD’s is made using scanning tunneling microscopy (STM) and scanning tunneling luminescence. The geometric structure of the islands is further investigated using cross-sectional transmission electron microscopy (TEM). The overgrowth occurs in three stages; initially the InP QD’s act as seeding points for the overgrowth, where the GaInP grows laterally from the side facets of the QD. The growth occurs preferentially in the [110] direction and elongated GaInP/InP islands are formed. As the overgrowth continues the islands increase laterally in size and GaInP also starts to grow between the islands, but not covering the top of the InP QD’s. The growth of GaInP on top of the QD’s commences once the islands have begun to coalesce. Using a model based on the STM and TEM results the electronic structures of the QD’s have been calculated by eight-band $\mathbf{k}\cdot \mathbf{p}$ theory. The calculations are in good agreement with the experimental results. Our findings unravel the details of the strain induced energy shift of the QD luminescence previously reported [Pistol et al., Appl. Phys. Lett. 67, 1438 (1995)].