MOCVD Epitaxy of Ultrawide Bandgap β-(Al_<i>x</i>Ga_1–<i>x</i>)₂O₃ with High-Al Composition on (100) β-Ga₂O₃ Substrates

Abstract

Single β-phase (100) (AlxGa1–x)2O3 thin films were successfully grown on (100) oriented β-Ga2O3 substrates via metalorganic chemical vapor deposition (MOCVD). By systematically tuning the precursor molar flow rates and growth conditions including chamber pressure, growth temperature and group VI/III molar ratio, pure β-phase (100) (AlxGa1–x)2O3 films with up to 52% of Al compositions were achieved. Comprehensive material characterization via X-ray diffraction (XRD) and high-resolution scanning transmission electron microscopy (HR-STEM) revealed high quality epitaxial growth of (100) β-(AlxGa1–x)2O3 films on (100) native substrates. High resolution X-ray spectroscopy (XPS) was used for determining the AlGaO bandgaps and the Al compositions. Two-dimensional defects in the β-(AlxGa1–x)2O3 films were investigated utilizing atomic resolution STEM imaging. Additionally, film characterization via HR-STEM imaging, XRD, and energy-dispersive X-ray spectroscopy (STEM-EDS) revealed coherent growth of high quality (100) β-(AlxGa1–x)2O3/Ga2O3 superlattice (SL) structures (x ≤ 50%) with abrupt interfaces and relatively uniform Al distribution. Step flow growth of (100) β-(AlxGa1–x)2O3 with smooth and featureless surface morphology was observed in AlGaO samples with high-Al compositions. A mechanism for the step-flow growth of high-Al content β-(AlxGa1–x)2O3 film is proposed by considering Al adatoms as preferred incorporation sites for AlGaO nucleation and growth.