Two-Step Formation of Gallium Droplets with High Controllability of Size and Density

We demonstrate the two-step formation of Ga droplets, which Consists Of the first formation at a high temperature followed by the second formation at a low temperature The droplets provide the Ga-richest surface, on which the second droplets start to nucleate almost immediately after deposition. This facilitates precise control of the amount second droplets, leading to the reproducible formation of small Ga droplets with low density. These Ga droplets are crystallized into GaAs quantum dots by irradiating As flux, which allows spectroscopy without sample fabrication.