MORPHOLOGICAL TRANSITION OF INAS ISLANDS ON GAAS(001) UPON DEPOSITIONOF A GAAS CAPPING LAYER

The interaction between a GaAs cap and InAs islands grown on vicinal G aAs(001) has been studied by transmission electron microscopy and atom ic force microscopy. Samples were prepared by molecular beam epitaxy a t 480 degrees C. Upon GaAs cap deposition, it was found that the previ ously grown InAs islands undergo a novel type of morphological transit ion, i.e., a transition from disk-shaped to ring-shaped islands. InAs becomes depleted or entirely absent in the central area of what had be en a disk-shaped InAs island. The GaAs cap was also shown to be virtua lly absent within the same central region, resulting in the formation of crater-like surface depressions.