Structure and composition profile of InAs/GaAs quantum dots capped by an InGaAs and InAlAs combination layer.

Cross-sectional transmission electron microscopy (X-TEM) and scan-TEM are performed to study how the structural properties of InAs/GaAs quantum dots (QDs) are affected when capped by an InGaAs and InAlAs combination layer (CBL), which currently is one of the most promising active regions for a 1.3 microm QD laser. GaAs capping causes leveling of the QDs, which is suppressed by the introduction of an InGaAs and InAlAs CBL. Scan-TEM results show that the CBL significantly suppresses In segregation and In-Ga intermixing during the capping process. Therefore, the height and In concentration in the buried QDs remain larger than that of GaAs capped QDs, leading to the enhanced optical properties of InAs QDs.