Band alignment of grafted monocrystalline Si (0 0 1)/β-Ga₂O₃ (0 1 0) p-n heterojunction determined by X-ray photoelectron spectroscopy

Beta-phase gallium oxide (β-Ga₂O₃) research has gained accelerated pace nowadays. However, the high acceptor activation energy obstructs the development of homojunction bipolar devices employing β-Ga₂O₃. The recently demonstrated semiconductor grafting technique provides an alternative and viable approach towards lattice-mismatched β-Ga₂O₃-based p-n heterojunctions with high quality interfaces. Understanding and quantitatively characterizing the band alignment of the grafted heterojunctions is crucial for future bipolar device development employing the grafting method. In this work, we present a systematic study of the band alignment in the grafted monocrystalline Si/β-Ga₂O₃ heterostructure by employing X-ray photoelectron spectroscopy (XPS). The band diagrams were constructed using two individual methods, the core level peak method and the valence band spectrum method, by utilizing the different portions of the measured data. Both methods resulted in an identical band alignment within the error range, which is also consistent with the prediction from the electron affinity values of Si and β-Ga₂O₃. The study suggests that the interface defect density in grafted Si/β-Ga₂O₃ heterostructures is at a sufficiently low level such that Fermi level pinning at the interface has been completely avoided and the universal electron affinity rule can be safely employed to construct the band diagrams of grafted monocrystalline Si/β-Ga₂O₃ heterostructures.