Size and site controlled Ga nanodots on GaAs seeded by focused ion beams

We present an approach for the generation of uniform metallic nanodots which, in contrast to conventional bottom up or top down processes, is based on a subtractive self-organization process relying on material decomposition induced by focused ion beam exposure. Nearly pure gallium dots were fabricated on GaAs (100) using a 50 keV Ga focused ion beam at normal incidence and a subsequent rapid thermal annealing. A dose of 2.5×1016 ions/cm2 can be considered as a threshold dose for the development of dots on GaAs (100). The diameters of these dots range from 120 to 850 nm with an aspect ratio of about 0.4 and a dot density of up to 7.23×107/cm2. Two-dimensional ordered arrays of embedded as well as freestanding Ga dots were fabricated by a site control technique relying on pre-patterned holes and an irradiation mediated migration and agglomeration.