Diffusion impact on thermal stability in self-assembled bilayer InAs/GaAs quantum dots (QDs)

The thermal stability of InAs/GaAs bilayer quantum dots structure has been investigated by photoluminescence (PL) measurements. The fabricated structure on thermal annealing PL shows no shift in peaks upto 650 degrees C indicating a robustness till a certain temperature making it a suitable candidate for vertical cavity surface emitting lasers (VCSELs) and feedback lasers where ideally a fixed wavelength is required. Integrated Photoluminescence gave a high activation energy in the range of 200 meV for the ground state PL peak for all the coupled structures. Above 650 degrees C there is a blue-shift in the PL peak. And at a very high temperature the dots start to diffuse into InAs wetting layer hence decreasing the quality of the crystal. The stability in the PL for temperatures below 650 degrees C can be accounted by strain energy as it works against the interdiffusion of QD and the seed layer till a certain temperature hence it compensates for the temperature effect but after 650 degrees Cw diffusion term becomes too strong and we observe a blue-shift in the peak. This can be justified theoretically by modifications in the Arrhenius diffusion equation. Due to this interdiffusion of In/Ga atom the dominance of the peak and the intensity of PL peak also changes as the QD composition changes [1-2]. Coupling the dots also leads to high activation energy which in-turn generates a stronger carrier confinement. But as the temperature increases, activation energy decreases weakening the carrier confinement potential because of interdiffusion between dot and seed layer.