Valence- and Conduction-Band Offsets for Atomic-Layer-Deposited Al2O3 on (010) (Al0.14Ga0.86)2O3.

The wide-bandgap ternary (Al_xGa_1−x)₂O₃ forms a heterostructure system with Ga₂O₃ that is attracting attention for modulation-doped field-effect transistors. The options for gate dielectric on (Al_xGa_1−x)₂O₃ are limited by the need for adequate band offsets at the heterointerface. Al₂O₃ deposited by atomic layer deposition (ALD) is one option due to its large bandgap (6.9 eV). We measured the valence-band offset at the Al₂O₃/(Al_0.14Ga_0.86)₂O₃ heterointerface using x-ray photoelectron spectroscopy (XPS). Al₂O₃ was deposited by ALD onto single-crystal β-(Al_0.14Ga_0.86)₂O₃ (bandgap 5.0 eV) grown by molecular beam epitaxy (MBE). The valence-band offset was determined to be 0.23 ± 0.04 eV (straddling gap, type I alignment) for ALD Al₂O₃ on β-(Al_0.14Ga_0.86)₂O₃. The conduction-band offset was 1.67 ± 0.30 eV, providing good electron confinement. [ABSTRACT FROM AUTHOR]