Time evolution of self-assembled GaAs quantum rings grown by droplet epitaxy

The correlation between the formation mechanism and the optical emission of GaAs quantum rings (QRs) is studied for the first time. The GaAs QRs were fabricated by the droplet epitaxy technique on Al0.3Ga0.7As surface using molecular beam epitaxy (MBE). Time evolution of these GaAs QRs with different arsenisation time is presented. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to observe the structural and geometrical changes during the formation of the GaAs QRs. Microstructural changes of the GaAs QRs were clearly seen in photoluminescence (PL) but barely observable in traditional surface spectroscopy techniques of SEM and AFM. This provides a new pathway to observe the microstructural changes of GaAs QRs growth. PL measurement showed that the emission peaks from the QRs changes from a single sharp peak to two sharp peaks at different stages of formation of the GaAs QRs. The splitting of PL peaks is a result of bimodal distribution of GaAs QRs formed during the droplet epitaxy process.

► Symmetrical GaAs quantum rings were grown by droplet expitaxy in a low As flux environment.
► The correlation between surface morphology and optical emission were examined with SEM, AFM and PL.
► The splitting of PL peaks indicates bimodal distribution of GaAs quantum rings.
► Smaller GaAs quantum rings forms later than larger GaAs quantum rings due to crystallisation saturation condition.
► PL provides a new way to understand GaAs quantum rings formation.