Abstract
In this thesis, the optical properties and surface morphologies of the self-assembled InAs quantum dots (QDs) are investigated. First, the InAs QDs grown on GaAsSb buffer layers with different Sb compositions are investigated. The enhanced InAs dot densities are obtained with increasing Sb composition. However, when the Sb composition exceeds 14 %, severe QD coalsence is observed. Second, the influence of GaAsSb strain-relaxed layers (SRLs) on the InAs QDs is investigated. Due to the strain-reducing effect, the enhanced photoluminescence (PL) intensity is demonstrated for the sample with the SRL. Also observed are the surface morphologies of InAs QDs with GaAs and GaAsSb partial capping layers. The results suggest that the GaAsSb partial capping layers are useful for maintaining the actual InAs QD surface morphology. Finally, the photoluminescence excitation (PLE) spectrums and spectral responses of InAs/GaAs QD infrared photodetectors with different InAs coverage are investigated. Increasing energy separation between heavy-hole state (HH) and light-hole state (LH) in the wetting layer (WL) region is observed in the QD PLE spectrums with increasing InAs coverage. The results suggest that most of the strain resulted from the InAs/GaAs lattice mismatch is accumulated in the WL instead of the QD region. Also observed are the similar energy separations of energy levels responsible for the intra-band absorption in the PLE spectrums of the QDIPs such that similar detection wavelengths are observed for the devices.