Photoreflectance study on InAs quantum well and quantum dots with quasi-monolayers

Room temperature photoreflectance (PR) was used to quantitatively investigate the change of band structure due to the strong confinement effects in the GaAs/InAs/GaAs hetero-structure with different InAs thickness of 1.2, 1.5 and 2.5 monolayer (ML). A series of transitions between electrons and holes in quantum well and quantum dots with quasi-ML are observed from the ML-dependent PR spectra, especially, the InAs QDs related PR peaks for 2.5 ML. Tho peaks from the InAs wetting laver, WL1 and WL2, are from the splitting of the degenerate valence hand of heavy hole (HH) and light hole (LH) due to the moderately high confinement. The variation in the splitting of HH and LH in the valence band with NIL is mainly caused by different confinement. Additionally, the data from ML-dependent PR measurement indicate that the transition from 2-dimension to 0-dimension of InAs related structure is observed optically.