Epitaxy and Characterization of h-BN/AlGaN Nanowire Heterostructures: Towards High Efficiency Light Emitters in the Ultraviolet-C Band

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Nontechnical description: This project is related to the development of a new generation of nanostructured wide bandgap semiconductor materials, which have the potential to enable efficient light emission in deep ultraviolet spectrum. If successfully developed, such materials promise new semiconductor light sources that can potentially replace conventional mercury lamps and excimer lasers for a broad range of applications, including water purification, sensing, and sterilization. For example, the replacement of mercury lamps by high efficiency solid-state ultraviolet lamps will eliminate mercury emissions to air, soil, and water and also significantly reduce electricity consumption for water processing and treatment. The broader impacts also include the highly interdisciplinary nature of the proposed research and the outreach to undergraduate, underrepresented minorities, and K-12. Students will be trained in a highly collaborative and interdisciplinary environment that includes materials design and theory (physics and materials science), nanomaterials growth/synthesis (materials science and electrical engineering), and characterization (materials science and engineering). Enhanced student training and teaching will also be achieved through characterization workshops and by developing and distributing state-of-the-art, open source software tool for offline processing electron microscopy data. Technical description: The overarching goal of this project is to investigate hexagonal boron nitride (h-BN) and aluminum gallium nitride (AlGaN) nanowire heterojunctions to enable efficient current injection and light emission in the deep ultraviolet wavelength range that was difficult to achieve in conventional wide bandgap materials. In this project, h-BN/AlGaN nanowire heterostuctures are grown by plasma-assisted molecular beam epitaxy and are characterized using a broad range of techniques, including transmission electron microscopy, scanning transmission electron microscopy, photoluminescence spectroscopy, micro-Raman spectroscopy, and X-ray diffraction. Due to the efficient surface strain relaxation, the use of nanowires can significantly reduce the formation of dislocations related to the lattice mismatch between h-BN and AlGaN and with the underlying substrate. More specifically, the research aims to demonstrate strong p-type conductivity of h-BN by exploiting the shallow acceptor-like boron vacancy formation, and realize h-BN/AlGaN heterojunctions wherein the p-type h-BN can function as deep ultraviolet transparent, conductive electrode. This could enable the replacement of conventional resistive and highly absorptive Ga(Al)N contact layers in current ultraviolet light emitters, and therefore promises ultraviolet light emitters with significantly enhanced efficiency. The effort is based on close interaction between two research groups with complementary expertise ensuring a closed loop between materials design and modeling, epitaxy, materials characterization, fabrication, and testing. Such an interdisciplinary, highly collaborative approach also provides a comprehensive training environment for both graduate and undergraduate students.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.