Scanning tunneling microscopy study on stacking processes of InAs dots on GaAs (001)

Scanning tunneling microscopy (STM) has been used to investigate the stacking processes of InAs quantum dots (QDs) formed on GaAs (001) substrates on an atomic scale. STM imaging reveals that for a coverage of 1.5 ML InAs, InAs islanding in the 2nd layer of stacked QD arrays selectively takes place on top of mounds produced by growth of GaAs capping layers. For a coverage of 1.6 ML InAs, InAs islands are grown on the whole surfaces including the mounds. At this stage, InAs islands formed on top of the mounds become much bigger than islands grown on terraces. We will discuss the selectivity of nucleation sites for the 2nd QDs in stacked QD arrays in terms of surface roughness produced by growth of GaAs capping layers as well as enhancement of adatom migration induced by surface strain fields.