Capping of InAs quantum dots grown on (311)B InP studied by cross-sectional scanning tunneling microscopy

Cross-sectional scanning tunneling microscopy was used to study at the atomic scale the impact of the capping material on the structural properties of self-assembled InAs quantum dots (QDs) grown on a high index (311)B InP substrate. Important differences were found in the capping process when InP or lattice matched InGaAs(P) alloys are used. The QDs capped with InP have a smaller height due to As/P exchange induced decomposition. This effect is not present when InGaAs is used as the capping material. However, in this case a strong strain driven phase separation appears, creating In rich regions above the QDs and degrading the dot/capping layer interface. If the InAs dots are capped by the quaternary alloy InGaAsP the phase separation is much weaker as compared to capping with InGaAs and well defined interfaces are obtained. (c) 2006 American Institute Of Physics.