Low-cost, low-defect Solvothermal growth of large diameter Gallium Nitride substrates

ABSTRACT: Availability of high quality, large area gallium nitride (GaN) single crystal substrates is one of the most outstanding issues for III-V nitride materials. Today's GaN device processes typically employ HVPE grown on sapphire and silicon carbide substrates, requiring elaborate buffer layers and deposition techniques to overcome lattice mismatch and dislocation densities up to 109/cm2. Kilowatt-level output power devices and advanced UV Lasers and Detectors will require true-bulk single-crystal GaN substrates for low-defect, reliable device structures. Solid State Scientific Corporation has developed a novel solvothermal crystal growth system for high quality GaN. Our process leverages past experience developing ultra-low-cost single-crystal quartz, and has already demonstrated 1 cm bulk GaN wafers with dislocation densities below 106/cm2. In cooperation with University of Massachusetts Lowell, Phase I will model the temperature profile, fluid-flow, and wall stress of our growth apparatus. That information will be leveraged to design and build a larger apparatus. In Phase II, our model will drive the new apparatus design and generate low-defect, large GaN wafers. In Phase III we will partner with a commercial manufacturer to provide custom, device-ready, epitaxial structures on low-defect ammono-thermal GaN substrates for high-power RF components and optoelectronic devices. BENEFIT: Successful scaling of an efficient apparatus to grow low-defect-density gallium nitride (GaN) requires a firm understanding of fluid flow, temperature, and material concentration fields. Such knowledge is best obtained through a program of a sophisticated numerical simulation of the transport phenomena occurring within the growth chamber, interactively coupled with detailed experimental efforts. This Phase I effort will include equilibrium simulation and experimental verification in order to design a scaled-up crystal growth chamber and process, which will duplicate and improve-upon excellent results already achieved in our smaller chambers. Scale-up of our growth chambers has two major advantages. First is the obvious increase in wafer size for more efficient semiconductor device fabrication. Second is the ability to accommodate multiple wafers (perhaps100's) in each growth cycle, taking advantage of batch economies. Realization of low-cost, high-quality, single-crystal, native substrates will bring order-of-magnitude improvement to GaN-based device capability,enabling advanced Air Force systems.