Influence of semiconductor cap layer on the impurity-free vacancy disordering of the In0.2Ga0.8As/GaAs multiquantum-well structure by dielectric capping layers

The feasibility of normal GaAs, low-temperature-grown GaAs (LT-GaAs) and low-temperature-grown InGaAs (LT-InGaAs) as the capping layers for impurity-free vacancy disordering (IFVD) of the In0.2Ga0.8As/GaAs multiquantum-well (MQW) structure has been studied. The normal GaAs, LT-GaAs and LT-InGaAs layers were tested as the outermost capping layer and the intermediate cap layer underneath the SiO2 or Si3N4 capping layer. The degree of quantum-well intermixing (QWI) induced by rapid thermal annealing was estimated by the shift of the photoluminescence (PL) peak energy. It was found that the IFVD of the In0.2Ga0.8As/GaAs MQW structure using LT-GaAs (LT-InGaAs) as the outermost capping layer was much smaller (larger) than that using a SiO2 (Si3N4) capping layer. It was also observed that the insertion of the normal GaAs, LT-GaAs and LT-InGaAs cap layers below the SiO2 or Si3N4 capping layer reduces the degree of QWI and the PL intensity after the QWI. A plausible explanation for the influence of normal GaAs, LT-GaAs and LT-InGaAs cap layers for the QWI of the InGaAs/GaAs structure is also discussed.