Impurity free vacancy disordering of InAs/GaAs quantum dot and InAs/InGaAs dot-in-a-well structures

Abstract

Two types of InAs quantum dot (QD) structure, grown by molecular-beam epitaxy on GaAs (100) substrates, one with dot-in-a-In0.12Ga0.88As quantum well (QW) and another one with dots embedded in a GaAs matrix, were intermixed by impurity free vacancy disordering method using SiO2 dielectric capping and rapid thermal annealing (RTA). The material and optical qualities of these structures were examined and compared by transmission electron microscopy (TEM) and low-temperature 5 K photoluminescence (PL) measurements. For both structures, significant blueshift of the PL spectra with increasing RTA temperature is observed. A maximum blueshift of up to 325 nm is observed from the InAs/InGaAs structure at a RTA temperature of 900 °C. Deduced from the reduction in dot height/diameter aspect ratio by TEM study and the reduction in PL peak separation for ground and excited states, it appears that QDs in dot-in-a-GaAs structure dissolved in a faster rate with increasing RTA temperature, attributed to the higher strain-induced interdiffusion in the InAs/GaAs structure. As opposed to InAs/GaAs QDs, InAs/InGaAs dots-in-a-well retained their optical quality and structural sharpness even after transforming into a QW at high annealing temperature, thus making this structure better candidate for monolithic photonic integration. © 2006 Elsevier B.V. All rights reserved.