LAUSR

Polarity-controlled GaN epitaxial films with Ga- and N-polarity are intentionally obtained by controlling annealing processes of ScAlMgO4 substrates. It is proved by high-angle annular dark-field scanning transmission electron microscopy, in situ reflection high-energy electron diffraction, and scanning electron microscopy that the GaN epitaxial films grown on ScAlMgO4 substrates annealed in an hydrogen atmosphere reveal Ga-polarity, whereas those grown on ScAlMgO4 substrates annealed in an ambient atmosphere show N-polarity. The thermodynamic mechanism of determining the crystal polarity is systematically investigated by first-principles calculations. It is concluded that N atoms prefer to deposit on the top of Ga atoms adsorbed onto Al(Mg)-face ScAlMgO4 substrates, leading to Ga-polarity, whereas Ga atoms preferentially stay on the central of three N atoms stacked onto the O-face ScAlMgO4 substrates, resulting in N-polarity. This work demonstrates a promising approach for the fabrication of GaN-based de...