Plasma-enhanced ALD growth of ε-(AlxGa1−x)2O3 alloy films with high Al content and tunable band offsets

Abstract

ε-(Al_xGa_1−x)₂O₃ alloys offer promising bandgap tunability for ultra-wide-bandgap semiconductor devices, yet high-Al-content epitaxy remains challenging due to phase segregation, defect generation, and compositional instability. Here, we report the first low-temperature epitaxial growth of high-quality ε-(Al_xGa_1−x)₂O₃ films up to x = 0.58 via plasma-enhanced atomic layer deposition (PEALD). The self-limiting layer-by-layer growth enables excellent compositional control, high crystalline quality, and notably low oxygen vacancy concentrations, even at high Al contents. Optical measurements show a linear bandgap increase with Al composition, confirming effective band structure engineering. Using in situ XPS within an ultra-high-vacuum (UHV) interconnection system, we quantitatively determine type-I band alignments at ε-(Al_xGa_1−x)₂O₃/ε-Ga₂O₃ heterointerfaces and identify large conduction band offsets, essential for two-dimensional electron gas formation in high-electron-mobility transistors. The combination of high material quality and tunable band offsets underscores the potential of PEALD-grown ε-(Al_xGa_1−x)₂O₃ for high-performance polarization-engineered electronics and deep-UV photonic devices.