Investigation of the effect of larger monolayer coverage in the active layer of bilayer InAs/GaAs quantum-dot structure and effects of post-growth annealing

Morphological and optical properties of MBE-grown single and bilayer InAs/GaAs quantum-dot heterostructure with comparatively larger monolayer coverage (similar to 3.3 ML) are investigated. As compared to the similar single-layer quantum-dot (SQD) structure, the bilayer quantum-dot (BQD) structure showed a more uniform spatial distribution and increased size homogeneity of the dots. It also exhibited longer wavelength photoluminescence (PL) emission at room temperature, with the peak at a wavelength (1.34 mu m) in the infrared communication window. The shift seen in the low temperature PL emission peak, even after annealing the BQD samples at temperatures up to 700A degrees C, is negligible. However, the BQD samples showed an activation energy lower than that of the SQD sample, attributed to the In/Ga interdiffusion with the thin (8.5 nm thick) GaAs spacer layer during the growth process. Despite that, the higher thermal stability demonstrated by the BQD structure, along with a lower linewidth, makes the bilayer quantum dots a desirable proposition for efficient lasing devices requiring strict tolerances on operating wavelength