GaN Lateral Overgrowth by Hydride Vapor Phase Epitaxy through Nanometer-Size Channels Fabricated with Nanoimprint Lithography

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Epitaxial lateral overgrowth (ELO) has been used for reducing the dislocation density to grow high-quality GaN crystals. In conventional ELO, micrometer-size channels formed on a mask material such as SiO<inf>2</inf>, where GaN growth starts, are generally used. In the present study, ELO through nanometer-size (50--80 nm) channels is investigated to improve the dislocation reduction ability. Channels are fabricated using nanoimprint lithography and dry etching. We demonstrate for the first time successful hydride vapor phase epitaxy (HVPE)-based GaN ELO growth through nanochannels. In the growth interface, distinct facet structures appear and coalescence between neighboring facets proceeds. The surface of a 20-μm-thick GaN layer becomes flat by the valleys between facet structures being buried. The dislocation density is shown to decrease to approximately 5\times 10^{7} cm<sup>-2</sup>for a 20-μm-thick GaN layer on sapphire. Photoluminescence measurements show a decay time of over 3 times longer than that of a conventional metalorganic chemical vapor deposition (MOCVD) template.
2013-08-25