Polarity inversion and growth mechanism of AlN layer grown on nitrided sapphire substrate using Ga-Al liquid-phase epitaxy

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.