NER: Synthesis of Nanoscale Structures of New Direct Bandgap Semiconductors

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We propose to conduct exploratory research on the fabrication of self-assembled nanometer-scale structures of new classes of semiconductors with direct tunable bandgaps in the UV/visible and infrared spectral regions.A major part of the work will focus on the growth of nanoscale sized structures of a completely new semiconductor system in the XCZN family where X is a group IV element (Si, Ge, Sn) and Z is a group III metal (Al, Ga, In). Specifically, these structures are quantum dots and pillars of the quaternary wideband gap material (GeC) 1-x (GaN) x with an adjustable bandgap between 1.6 and 3.3 eV. These materials are created directly on Si via suitable buffer layers utilizing the vapor-liquid-solid (VLS) mechanism, which provides flexibility of fine-tuning the size and spatial distributions of the nanostructures. An important objective of this work is to integrate (GeC) 1-x(GaN)x and related optical alloys with Si technologies so that their full potential can be realized as commercially viable materials.The research program also covers the synthesis of infrared nanostructures in the Si-Ge-Sn system with tunable electronic and structural properties. These materials include Ge1-xSnx quantum dots as well as related (SiGe) 1-xSnx and (Si4Ge) 1-xSnx nanostructures created directly on silicon substrates. The novelty in this case is the direct-bandgap nature of these Si-based systems. The electronic structure and optical properties will be thoroughly studied by spectroscopic ellipsometry, Raman microprobe, photoluminescence, cathodoluminescence, transmission IR spectroscopy and electron energy loss spectroscopy. Structural characterization involving high resolution electron microscopy, ion channeling (RBS), high resolution x-ray diffraction, low energy electron microscopy (LEEM) and atomic force microscopy are used extensively to provide rapid feedback about the quality of the structure and morphology of the nanostructures, thus ultimately leading to better design of the synthetic pathways.The broader impact of the proposed activity is to benefit undergraduates in chemistry, physics and materials science, by involving them in the research and discovery process of creating novel nanostructures of new and useful semiconductor materials. These students, including members of underrepresented groups, will also be exposed to the industrial environment at local microelectronic and optoelectronic laboratories in order to gain first-hand knowledge and an in-depth appreciation of the technical innovations in semiconductor and nanoscience research