Abstract
The surface morphology and optical characteristic of InAs QDs with varied coverage were investigated. With the thickest coverage 2.6 ML in our experiment, two-group size distribution of QDs was observed. The coalescence of InAs QDs are responsible for the formation of these large-size InAs QDs. These large QDs existence results in the PL blue shift with increasing pumping power density. And the red shift of ground state transition with increasing coverage can be attributed to the increasing height of QDs. We have successfully deposited the high quality InAs/GaAs QD samples by the post-growth annealing. The AFM images show the annealing time of 60 seconds at 485 ℃ is proper to grow the QD samples with lower density. Nonetheless, longer annealing time may cause the In adatoms desorption and reduce the integrated PL intensity. Annealing temperature seems to be a more important parameter than annealing time when we attempt to control the QD density and get better quality. Higher temperature about 500 ℃ is helpful to reduce the QD density without producing an unexpected peak in PL spectrum. However, power-dependent and temperature-dependent micro-PL results indicate that the unexpected peak appear in the sample annealed at 515 ℃ should originate from the shallow defects or surface states in the interface between InAs QDs and GaAs barrier layer.