Epitaxial growth of β-Ga2O3 (−201) thin film on four-fold symmetry CeO2 (001) substrate for heterogeneous integrations

Abstract

β-Ga₂O₃ is a wide bandgap semiconductor material that is promising for many fields such as gas sensors, UV detectors, and high-power electronics. Until now, most epitaxial β-Ga₂O₃ thin films could only be realized on six-fold symmetric single crystal substrates including sapphire (0001), 3C-SiC (001), and native β-Ga₂O₃. In this report, we demonstrate the epitaxial growth of β-Ga₂O₃ (−201) thin films on non-six-fold symmetric substrates, i.e., the CeO₂ (001) substrate. Different from the conventional six-fold symmetric sapphire substrates, the four-fold symmetric cubic phase CeO₂ (001) induces the formation of two sets of hexagonal-like atom frameworks with a mutual rotation angle of 90° in the β-Ga₂O₃ (−201) plane. This is due to the small lattice mismatch between the β-Ga₂O₃ (−201) plane and the CeO₂ (001) plane in two directions: CeO₂ [100]//β-Ga₂O₃ [010] and CeO₂ [010]//β-Ga₂O₃ [010]. Besides, the valence band offset (VBO) and the conduction band offset (CBO) at the β-Ga₂O₃/CeO₂ heterojunction are examined using high-resolution X-ray photoelectron spectroscopy (HR-XPS) and are estimated to be 1.63 eV and 0.18 eV, respectively, suggesting a type-II heterostructure. The obtained epitaxial β-Ga₂O₃ thin films are fabricated into photodetectors (PDs), which show key photoelectrical characteristics that are similar to those of PDs using the conventional sapphire substrate. The results indicate the epitaxial β-Ga₂O₃ thin films on CeO₂ have a high crystallization quality, and thus are capable of producing various essential devices. Moreover, the epitaxy between β-Ga₂O₃ (−201) and CeO₂ (001) demonstrated in this work can pave the way for constructing heterostructures between β-Ga₂O₃ and other cubic-phase functional materials, such as p-type semiconductors, piezoelectric semiconductors, and superconductors.