CAREER: Developing Advanced Morphological Control of Nanowires to Encode Photonic and Optoelectronic Functionality

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Nontechnical Description: Semiconductor nanowires have been widely explored for their potential electronic and photonic applications, and the properties of the wires are largely dictated by the ability to modulate their composition during synthesis. This project aims to explore chemistry-based processes to encode complex cylindrical silicon wires and to understand the incorporation of phosphorus, boron, and nitrogen dopant atoms in silicon nanowires during their growth. The effect of wire synthesis conditions on the concentration and spatial profiles of these dopant atoms is studied, and the potential for atomically-abrupt interfaces is evaluated. In addition, the influence of the dopant atoms on the optical properties and shape of the wires is examined, targeting optimized growth of spiraling nanowires and controllable creation of luminescent centers within the wires. The project trains undergraduate and graduate students in topics that bridge the interface between chemistry, physics, and engineering - providing breadth of experience in nanomaterials synthesis, microfabrication, optoelectronic measurements, and modeling. Various programs and demonstrations in elementary schools and local libraries, annual public science expositions and summer research for high-school students enable broad dissemination of the scientific concepts. Technical Description: Semiconductor nanowires are often synthesized by metal-catalyzed growth using vapor-liquid-solid (VLS) and vapor-solid-solid (VSS) growth processes. This project aims to develop a combined VLS-VSS growth method to encode phosphorus, boron, and nitrogen dopant atoms in silicon nanowires with single or sub-nanometer spatial resolution. The incorporation of dopants is used to modulate the optical properties and morphology of the nanowires. For instance, co-doping is explored as a novel method to create chiral wires, and the chiro-optical response of these structures is studied. In addition, the incorporation of nitrogen is used to introduce defect states with luminescent characteristics. Modulation of boron and phosphorus is employed to create deep-subwavelength photonic crystal cavities integrated with p-n junction photodetectors that exhibit wavelength-selective detection. These efforts expand the set of bottom-up synthetic methods that can be used to encode photonic and optoelectronic functionality in nanowires.