We have studied the morphology evolution of holed nanostructures formed by aluminum droplet epitaxy on a
GaAs surface. Unique outer rings with concentric inner holed rings were observed. Further, an empirical
equation to describe the size distribution of the outer rings in the holed nanostructures has been established.
The contour line generated by the equation provides physical insights into quantum ring formation by droplets
of group Ⅲ materials on Ⅲ–Ⅴ substrates.