22 217 5178 A novel liquid phase epitaxy method was proposed for growing an AlN layer using Ga-Al binary flux under normal pressure. In this method, nitrogen gas was injected into the flux. Then a nitrided sapphire substrate was used as a template to achieve homoepitaxial growth. Advantages of using a nitrided sapphire substrate were demonstrated; the optimum flux composition was investigated. We grew 1-mm-thick c-axis oriented AlN layer for 5 h at 1573 K. The full width at half maximum values of X-ray rocking curves for AlN (0002) and (10À12) were, respectively, 50 and 590 arcsec. Moreover, the surface morphology and interfacial structure were observed using a scanning electron microscope, laser microscope, and highresolution transmission electron microscope.

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22 217 5178 Previously, we developed Ga-Al liquid-phase epitaxy (LPE) to grow AlN layers on a surface nitrided sapphire substrate using Ga-Al solutions. We found that polarity inversion occurs at the interface between the nitrided sapphire layer and the LPE layer. As the partial pressure of oxygen influences LPE growth, our current study investigated this growth by controlling oxygen in supplying nitrogen gas. Combined with the previous study, we discuss these results in light of the polarity inversion model and growth mechanism for the Ga-Al LPE technique. Oxygen atoms are believed to dissolve in the solution and get trapped on the surface of nitrided sapphire. The trapped oxygen atoms form a symmetrical octahedral structure, which resets the polarity of the nitrided sapphire. Consequently, chemically stable aluminum-polar AlN can be grown in the solution.