  Shape transformations of partially capped self-assembled InAs quantum dots
grown on InP are studied. Atomic force microscopy images show large anisotropic
redistribution of the island material after coverage by a 1 nm thick InP layer.
The anisotropic material redistribution occurs within a few minutes and leads
to a change from lens-like to elongated ring-like islands. The shape
transformation is not accompanied by dot material compositional change. The
formation of InAs/InP quantum rings disagrees with a previous model of
InAs/GaAs ring formation that assumes that the driving force for the dot to
ring transformation is the difference in surface diffusion velocity of indium
and gallium atoms.
