LAUSR

Abstract In-situ molecular beam epitaxy (MBE) Y 2 O 3 films 1–2 nm thick were epitaxially grown on GaAs(001)−4×6 reconstructed surfaces. Despite a large lattice mismatch, the hetero-structure exhibits outstanding thermal stability to 900 °C with excellent capacitance-voltage ( C-V ) characteristics. Low interfacial trap densities ( D it 's ) of (3–5)×10 11  eV −1  cm −2 were obtained using the conductance method ( G-V ) without discernible peaks at the mid-gap. The frequency dispersion of the measured C-V s of the Y 2 O 3 /GaAs(001) is ~4.6% for p -GaAs and ~12.4% for n -GaAs. In contrast, the atomic layer deposited Al 2 O 3 on GaAs(001) shows large D it with a peak at the mid-gap, large C-V frequency dispersion, and low thermal stability at temperatures higher than 600 °C. Synchrotron radiation photoemission results show intactness of the interfacial structure in the MBE-Y 2 O 3 /GaAs, while removal of the surface As atoms is found in the ALD-Al 2 O 3 /GaAs system.