Initial Stages of Growth of Gallium Nitride via Iodine Vapor Phase Epitaxy
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E3.23.1
Initial Stages of Growth of Gallium Nitride via Iodine Vapor Phase Epitaxy WJ Mecouch*,1, BJ Rodriguez2, ZJ Reitmeier1, J-S Park1, RF Davis1, Z Sitar1 Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695 2 Department of Physics, North Carolina State University, Raleigh, NC 27695 1
Abstract Thin layers of GaN have been deposited on 1µm thick MOVPE GaN(0001) thin film substrates using a novel vertical iodine vapor phase epitaxy system. The system features three concentric flow zones that separate the reactant gasses until they reach the substrate. Hydrogen flows through the innermost zone to deliver iodine vapor from an external bubbler to the molten Ga maintained at ~1050°C and GaI to the substrate; high-purity ammonia flows through the outermost zone; nitrogen flows through the middle zone to prevent reaction between the growth species at the GaI nozzle. GaN growth was found to be a function of time, with decreasing concentration of iodine the likely cause of a decrease in growth rate at longer growth times. The step-and-terrace microstructure of the MOVPE seeds was replaced with a smooth morphology film after the shortest growth experiment. Star-shaped features with hexagonal symmetry grew on the surface with increasing growth time. These features became the tops of hexagonal pyramids; these pyramids grew competitively and dominated the final growth surface. The surface of the films grown for the longest period contained a step-and-terrace microstructure; however, the density of steps of was lower than that on the surface of underlying MOVPE substrate. Introduction Hydride vapor phase epitaxy (HVPE) has long been used for growing thick layers of GaN having a reduced density of threading dislocations [1] relative to the densities of these defects within thin films of this material grown via MOVPE and MBE. The most common HVPE process route involves the reaction of flowing HCl with the surface of molten Ga to form GaCl vapor which is transported to the substrate and which reacts with flowing NH3 to grow a GaN layer. Sufficiently thick layers can be separated from substrates having a different chemistry via, e.g. laser liftoff [2], and used as stand-alone substrates for the growth of GaN-based material device layers [3]. The reduction in the defect density realized in both the bulk-like GaN substrates and the subsequently grown layers has been associated with the improved performance of blue [4], near-ultraviolet [4] and ultraviolet light emitting diodes [5]. A less chemically aggressive alternative to HCl-based HVPE has been developed [6,7] which uses iodine as a substitute for HCl and is referred to as iodine vapor phase growth (IVPG). A horizontal reactor was employed in the process route described in Refs. [6,7]. Growth rates to 32 µm/hr [7] were reported. A unique vertical, up-flow reactor is being used in the present research to investigate the initial stages of IVPG of GaN. The experimental approach and the results and summary of this study are presented
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