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15 March 2016 Diffusion impact on thermal stability in self-assembled bilayer InAs/GaAs quantum dots (QDs)
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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°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°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°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°C 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.
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B. Tongbram, Navneet Sehara, Jashan Singhal, Debabrata Das, D. Prasad Panda, and S. Chakrabarti "Diffusion impact on thermal stability in self-assembled bilayer InAs/GaAs quantum dots (QDs)", Proc. SPIE 9758, Quantum Dots and Nanostructures: Growth, Characterization, and Modeling XIII, 97580T (15 March 2016);

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