Fabrication of Ga-templates Using a Focused Ion Beam
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Fabrication of Ga-templates Using a Focused Ion Beam Hao Wang, Greg C. Hartman, Joshua Williams, Jennifer L. Gray Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, PA 15261, USA ABSTRACT There are many factors that have the potential to limit significant advances in device technology. These include the ability to arrange materials at shrinking dimensions and the ability to successfully integrate new materials with better properties or new functionalities. To overcome these limitations, the development of advanced processing methods that can organize various combinations of materials at nano-scale dimensions with the necessary quality and reliability is required. We have explored using a gallium focused ion beam (FIB) as a method of integrating highly mismatched materials with silicon by creating template patterns directly on Si with nanoscale resolution. These templates are potentially useful as a means of locally controlling topography at nanoscale dimensions or as a means of locally implanting Ga at specific surface sites. We have annealed these templates in vacuum to study the effects of ion dosage on local Ga concentration and topography. We have also investigated the feasibility of creating Ga nanodots using this method that could eventually be converted to GaN through a nitridation process. Atomic force microscopy and electron microscopy characterization of the resulting structures are shown for a variety of patterning and processing conditions. INTRODUCTION Direct band gap semiconductors such as gallium nitride (GaN) are attractive for many semiconductor optical device applications. The band gap of GaN specifically is 3.4 eV at 300 °K [1],and it is widely used in electrically pumped ultraviolet–blue light-emitting diodes, lasers, photo detectors, and potentially for single photon sources [2-4]. There has been considerable effort devoted to synthesizing two dimensional structures (thin films) and one-dimensional structures (nanowires and nanorods) [5-9] via several routes including template-induced growth [10] or laser-evaporation [11]. However, zero-dimension structures are of interest for quantum dot device applications due to their discrete energy spectrum and more importantly, because they exhibit genuine few-carrier effects. There has been a significant amount of research carried out in synthesizing quantum dots in general; however demonstrating growth of gallium nitride quantum dots directly on silicon, the most technologically important substrate, is a challenge. The primary objective of this study is to grow gallium nanodot templates, to be used as a source of gallium for the eventual conversion to GaN, on a silicon substrate using a focused ion beam direct patterning method. Such a method can be applied to controllably form gallium nanodots of specific sizes at a particular position on the substrate to create new device structures. Since an un-doped silicon substrate itself contains no trace of gallium, the technique discussed here employs
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