Shape and surface morphology changes during the initial stages of encapsulation of InAs/GaAs quantum dots

Abstract

The change in shape and surface morphology of InAs/GaAs(0 0 1) quantum dots (QDs) during their initial encapsulation by GaAs has been studied using reflection high energy electron diffraction (RHEED) and scanning tunnelling microscopy (STM). The shape of the QDs changes significantly during the earliest stages of overgrowth. In situ RHEED measurements show a significant chevron angle change after deposition of only 2 ML of GaAs, before losing all crystallographic structure as more GaAs is deposited. STM results indicate significant surface mass transport, the height of the QDs decreases faster than the rate at which the GaAs capping layer is deposited and the QDs effectively “collapse” during the earliest stages of encapsulation. The area of the partially capped QDs increases significantly with increasing GaAs deposition and there is an anistropic increase in shape with significant elongation along the [ 1 ̄ 1 0] azimuth.