In Situ Oxidation of GaN Layer and Its Effect on Structural Properties of Ga₂O₃ Films Grown by Plasma-Assisted Molecular Beam Epitaxy

Abstract

Plasma-assisted molecular beam epitaxy (PAMBE) was used to grow Ga₂O₃ films on oxidized GaN layers on nitrided sapphire substrates. The GaN layer was grown by PAMBE, and the in situ oxidation of the GaN layer was achieved through exposure to oxygen plasma, which resulted in the formation of monoclinic β-Ga₂O₃. Crystalline monoclinic β-Ga₂O₃ films were grown on the GaN layers, with and without oxidation. The orientation relationships were [$11\overline{2} 0$] Al₂O₃//[$1\overline{1} 00$] AlN//[$1\overline{1} 00$] GaN//[102] β-Ga₂O₃ and [$1\overline{1} 00$] Al₂O₃//[$11\overline{2} 0$] AlN//[$11\overline{2} 0$] GaN//[010] β-Ga₂O₃. The grown β-Ga₂O₃ films were not single-crystalline but showed rotational domains along the growth direction with three variations, which resulted in six-fold rotational symmetry instead of two-fold rotational symmetry. The surface roughness of the grown β-Ga₂O₃ film was closely reflected to that of as-grown GaN and oxidized GaN. By analyzing the x-ray omega rocking curves for the on-axis ($\overline{2} 01$) and off-axis (002) reflections, it was concluded that rotational domains dominantly affected the crystal quality of the β-Ga₂O₃ films.