Characterization of Gallium Nitride Grown on (0001) Sapphire by Plasma-Enhanced Atomic Layer Epitaxy

α-GaN thin films have been grown on (0001) sapphire by a plasma-enhanced atomic layer epitaxy (PEALE) technique using a GaN buffer layer grown at lower temperatures. Both single crystal and polycrystal thin films have been obtained depending on the growth conditions, particularly, oxygen contamination of the plasma source and the substrate temperature. The orientation relationship between the single crystal film and the substrate is [0001]GaN//[0001]Al2O3, % MathType!MTEF!2!1!+- % feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqr1ngB % PrgifHhDYfgasaacH8srps0lbbf9q8WrFfeuY-Hhbbf9v8qqaqFr0x % c9pk0xbba9q8WqFfea0-yr0RYxir-Jbba9q8aq0-yq-He9q8qqQ8fr % Fve9Fve9Ff0dmeaabaqaciGacaGaaeqabaWaaeaaeaaakeaadaWada % qaaiaaigdaceaIXaGbaebacaaIWaGaaGimaaGaay5waiaaw2faaiaa % bEeacaqGHbGaaeOtaiaac+cacaGGVaWaamWaaeaacaaIXaGabGOmay % aaraGaaGymaiaaicdaaiaawUfacaGLDbaacaqGbbGaaeiBamaaBaaa % leaacaaIYaaabeaakiaab+eadaWgaaWcbaGaaG4maaqabaaaaa!49DA! $$\left[ {1\bar 100} \right]{\text{GaN}}//\left[ {1\bar 210} \right]{\text{A}}{{\text{l}}_2}{{\text{O}}_3}$$ and % MathType!MTEF!2!1!+- % feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqr1ngB % PrgifHhDYfgasaacH8srps0lbbf9q8WrFfeuY-Hhbbf9v8qqaqFr0x % c9pk0xbba9q8WqFfea0-yr0RYxir-Jbba9q8aq0-yq-He9q8qqQ8fr % Fve9Fve9Ff0dmeaabaqaciGacaGaaeqabaWaaeaaeaaakeaadaWada % qaaiaaikdaceaIXaGbaebaceaIXaGbaebacaaIWaaacaGLBbGaayzx % aaGaae4raiaabggacaqGobGaai4laiaac+cadaWadaqaaiaaigdace % aIXaGbaebacaaIWaGaaGimaaGaay5waiaaw2faaiaabgeacaqGSbWa % aSbaaSqaaiaaikdaaeqaaOGaae4tamaaBaaaleaacaaIZaaabeaaaa % a!49F2! $$\left[ {2\bar 1\bar 10} \right]{\text{GaN}}//\left[ {1\bar 100} \right]{\text{A}}{{\text{l}}_2}{{\text{O}}_3}$$ . The polycrystalline film has the c-axis perpendicular to the substrate and contains the same orientation found in the single crystal film. However, two additional orientations have been found that are rotated approximately ±19° from the single crystal orientation. The defect structures at the film/substrate interface were investigated by various X-ray methods such as rocking curves and phi scans, along with plane-view and cross sectional TEM. Possible growth mechanisms of both the single crystal and polycrystalline films will be discussed.