Band alignment modulation of atomic layer deposition-prepared Al₂O₃/β-Ga₂O₃ heterojunction interface by deposition temperature

The band alignment between oxygen plasma-assisted atomic layer deposition Al₂O₃ films and β-Ga₂O₃ (−201) substrates under different deposition temperatures was characterized by x-ray photoelectron spectroscopy. As the deposition temperature increased from 30 to 200 °C, all the heterojunctions exhibited a type-I alignment. The bandgap of Al₂O₃ enlarged from 6.26 ± 0.1 to 6.81 ± 0.1 eV, leading to the conduction band offset varying linearly from 1.39 ± 0.1 to 1.95 ± 0.1 eV, while the valence band offset was insensitive. This difference was attributed to Al ion deficiency and hydroxyl groups induced by an inadequate reaction of trimethylaluminum under low deposition temperatures, which was proved by secondary ion mass spectrometry (SIMs) and Fourier-transform infrared spectroscopy (FTIR). These findings could facilitate the design of a CBO-controllable Al₂O₃/β-Ga₂O₃ heterojunction through deposition temperature.