Effects of the thickness of dielectric capping layer and the distance of quantum wells from the sample surface on the intermixing of In0.2Ga0.8As/GaAs multiple quantum well structures by impurity-free vacancy disordering

We investigated the effects of the thickness of SiO2 and Si3N4 capping layer and the distance of quantum wells from the sample surface on the intermixing of In0.2Ga0.8As/GaAs multiple quantum well (MQW) structures by impurity-free vacancy disordering. It was found that the thin SiO2 capping layer of 25 nm suppressed the QW intermixing (QWI) due to the saturation of out-diffused Ga atoms and the reduction of porosity induced into the capping layer. The QWI remained constant for the samples capped with SiO2 thickness above 50 nm. The degradation of Si3N4 films was observed after rapid thermal annealing for the MWQ samples capped with thick Si3N4 of above 300 nm. From the investigation of QW structural parameters on the QWI, the magnitude of blueshift increases with decreasing distance of QWs from the sample surface.