Segregation-driven formation of bismuth quantum dots in parabolic GaAsBi/AlGaAs quantum structures

This work is focused to investigation of bismuth quantum dots formation mechanism using segregation process via two types of annealing of gallium arsenide bismide quantum well structures with aluminium gallium arsenide parabolic barriers: in-situ annealing in a molecular beam epitaxy reactor immediately after growth and ex-situ in a rapid thermal annealing oven. Both processes were performed in the range of temperatures of 600-750 °C and adjusting annealing time from 0 to 180 s. The structures were characterized using high resolution transmission electron microscopy, temperature and time dependent photoluminescence measurements, cathodoluminescence, Raman spectroscopy, and dimensional analysis. Transmission electron microscopy images demonstrated that in-situ annealing in a reactor at temperatures up to 750 °C for 0–150 s results in the formation of randomly oriented Bi quantum dots with a dominant size of about 10–15 nm, exhibiting cathodoluminescence at 0.9 eV at 10 K. The investigation using ex-situ rapid thermal annealing showed a trend that with increase of annealing temperature the intensity of quantum well related emission reduces, peak is redshifted and broadens, while the quantum dot related emission increases in intensity, suggesting the diffusion of bismuth atoms from the bismide lattice leading to formation of pure bismuth quantum dots.