GaSb/GaAs quantum-ring-with-dot structures grown by droplet epitaxy

We have studied the growth of GaSb/GaAs nanostructures by droplet epitaxy with the variation of Ga deposition temperature which is one of the key parameters. With the use of low Sb flux, GaSb quantum rings (QRs) were formed as a result of the outward diffusion of Ga atoms from the droplets during crystallization. An increase of the deposition temperature results in the larger QR size and the lower QR density due to the longer diffusion length of Ga atoms, which gives rise to the larger initial droplets. Interestingly, some portion of QR lobe breaks up and transforms into a quantum dot (QD) so as to reduce the mismatch strain. A nanostructure containing both QR and QD is called a quantum-ring-with-dot structure (QRDS). As the deposition temperature increases, the nanostructure height distribution changes from unimodal to bimodal behaviors owing to the significant difference between QR and QD heights, whereas the nanostructure diameter still exhibits a unimodal distribution. The bimodal height distribution strongly affects the optical properties and the dynamic of thermal-excited carriers.