Asymmetrical $In0.1Ga0.9As/Al0.3Ga0.7As$ quantum rings and their optical properties

$In0.1Ga0.9As/Al0.3Ga0.7As$ quantum rings were fabricated by droplet epitaxy technique using molecular beam epitaxy (MBE). 7.5 ML $In0.1Ga0.9As$ droplets are deposited on $Al0.3Ga0.7As$ epitaxial layer at 350°C and 250°C. After that, they were crystallized under As₄ pressure of 8×10⁻⁶ torr at 250°C. The surface morphology of quantum rings is studied by atomic force microscopy. It is found that quantum rings are not symmetrical due to anisotropic behavior of In and Ga atom migration during crystallization process. The quantum ring density of the sample deposition at 350°C and 250°C are 1×10⁹ cm⁻² and 2.6×10⁹ cm⁻², respectively. Consequently, the asymmetric quantum rings with deposition at 350°C give two photoluminescence (PL) peaks at 1.27 and 1.38 eV at 20K. However, the PL peak of quantum rings with deposition at 350°C is merged with GaAs peak due to the poor size distribution.