Solar-blind UV Schottky barrier photodetectors formed by Au/Ni on β-(Al_xGa_1−x)₂O₃/AlGaN heterostructures

In this study, (Al_xGa_1−x)₂O₃ films are formed through thermal oxidation on Al_xGa_1−xN/n-GaN heteroepitaxial layers. The process temperature and duration time are controlled to leave a part of the Al_xGa_1−xN layer and form (Al_xGa_1−x)₂O₃/Al_xGa_1−xN/n-GaN heterostructures. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses are performed on the thermally treated Al_xGa_1−xN to determine the presence of (Al_xGa_1−x)₂O₃ films in the Al_xGa_1−xN/n-GaN heteroepitaxial layers. The oxidized Al_xGa_1−xN and GaN layers exhibit XRD peaks at 59.2° and 59.4° corresponding to the diffraction (6̄03) planes of β-Ga₂O₃ and β-(Al_xGa_1−x)₂O₃ phases, respectively. The XPS spectra of the Ga3d and O1s core levels peak at 20.5 and 531.1 eV, confirming the presence of Ga-O bonds, i.e., the formation of a Ga₂O₃ and/or (Al_xGa_1−x)₂O₃ thin film. In particular, Ni/Au and Ti/Al bilayer metal contacts are deposited on the (Al_xGa_1−x)₂O₃ and n-GaN layers, respectively, in the (Al_xGa_1−x)₂O₃/Al_xGa_1−xN/n-GaN heterostructures to form Schottky barrier photodetectors (SB PDs). Under a reverse bias of 1 V, (Al_xGa_1−x)₂O₃ SB PDs exhibit a typical responsivity of around 6 A W⁻¹ with an incident light wavelength of 225 nm, and the rejection ratio (at 225 nm vs. at 370 nm) of responsivity is as high as ∼104. In addition, two cut-off wavelengths at 225 and 330 nm correspond to the bandgaps of (Al_xGa_1−x)₂O₃ and Al_xGa_1−xN layers, respectively, in the (Al_xGa_1−x)₂O₃/Al_xGa_1−xN/n-GaN heterostructures, and the Al content in (Al_xGa_1−x)₂O₃ is 16%.