We report on a high-quality α-Ga2O3 epilayer grown on a sapphire (0001) substrate by suppressing the pre-reaction between the main precursors, GaCl and GaCl3, and O2.

The formation of n-Ga2O3/p-GaN heterojunctions has been studied intensively due to the lack of p-Ga2O3. Metalorganic chemical vapor deposition (MOCVD) is known to provide a high-quality heterojunction of n-Ga2O3/p-GaN compared to thermal oxidation, sputtering, or pulsed-laser deposition (PLD). In this work, single-crystalline β-Ga2O3 of {−201} is grown on a GaN (001)/Al2O3 substrate using MOCVD. An abrupt heterojunction without a noticeable interfacial layer is observed between β-Ga2O3 and GaN. However, due to the lattice mismatch between β-Ga2O3 (−201) and GaN (001), grain boundaries and grain defects originating from the Ga2O3/GaN interface continue in β-Ga2O3 in a diagonal direction. The epitaxial nature of the grown β-Ga2O3 on the GaN (001)/Al2O3 substrate causes the nanorod-shaped morphology in the growth direction of β-Ga2O3. This work marks a step toward the formation of a high-quality heterojunction of Ga2O3/GaN, which would serve as an essential building block for various devices, including optoelectronics and power electronics.