Self-organization of gallium metal droplets on a gallium arsenide surface

Sputtering by focused ion beam is utilized for patterning of a GaAs(001) surface. The morphological evolution of a flat surface is studied as a function of ion beam energy, incidence, current, sputter time, and dwell time. Two-dimensional arrays of self-organized Ga droplets are observed. The ordering of Ga nanodroplets occurs at off-normal incidence for low-energy sputtering with controlled density and size of the droplets. In addition, surface nanostructuring by subsequent sputtering is demonstrated as an effective technique for creating more complex periodic patterns characterized by three-dimensional droplet ordering. The morphological evolution of the surface is explained with Sigmund theory for curvature-dependent sputtering [1], Bradley-Harper model for surface instability [2], and a model for propagation of tall steep slopes based on the dynamics of shock wave propagation [3]. The theoretical model for droplet ordering is based on preferential sputtering and shadowing effects [4]. The pre-patterned GaAs substrates will serve as templates for epitaxial growth of ordered crystalline structures utilizing local droplet etching (LDE) technique [5]. Optical and electric transport characterization of the epitaxial nanostructures will shed light on their application in fabricating new optoelectronic devices.