| Summary: | 碩士 === 國立臺灣大學 === 材料科學與工程學研究所 === 95 === GaN have been an attractive material for optoelectronic applications in blue-green light emitting diodes and blue laser diodes due to there excellent property. GaN thin film deposited on heterogeneous substrates bring a drawback in film quality because of lack of GaN substrates. The ammonothermal method is a potential method to synthesize high quality single crystal of GaN for homogeneous substrates.
GaN were synthesized by ammonothermal using three kinds of acid mineralizer (NH4Cl、NH4Br、NH4I) at different process temperature. Precursor (gallium), solvent (ammonia) and mineralizer were sealed in the autoclave. The solvent can be brought to supercritical fluid by increasing temperature and pressure above critical point of solvent. Gallium dissolved in supercritical ammonia to form gallium-containing intermediates and then intermediates converted to crystalline phase of GaN.
As the result, using NH4Cl as a mineralizer can synthesize GaN at lower temperature. It seems to be more effect to form GaN compared to other acid minerlizers. In SEM, it shows agglomerate GaN composed of nanoparticales. Depending on XRD, Both wurtzite structure and zinc-blende structure were obtained in ammonothermal synthesis. Using NH4Cl favors wurtzite GaN while using NH4Br and NH4I favor zinc-blende GaN
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