Band Alignment and Interface Recombination in NiO/<i>β</i>-Ga₂O₃ Type-II p-n Heterojunctions

Abstract

Engineering oxide interfaces with defined electronic band structures is of vital importance for designing all-oxide devices with controllable multifunctionalityand improved performance. Here, we report the band alignment, band bending, and transport mechanism in the NiO/β-Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> p-n heterojunction (HJ) which exhibits high performances with a rectification ratio over 1011, a turn-on voltage of 1.87 V and specific ON-resistance of 10.2 mΩ·cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . A typeII band alignment is identified at NiO/β-Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> HJs with a valence band offset of 3.60 eV and a conduction band offset of 2.68 eV, respectively, determined from the depth-profiled X-ray photoelectron spectroscopic analysis. Besides band edge discontinuity, an additional built-in potential of 0.78 V is observed at the interface due to the charge transfer across the p-n-junction. In comparison, the NiO/β-Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> p-n HJ has lower leakage current and higher breakdown voltage than that of the Ni/Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Schottky barrier diode. Capacitance- frequency analysis indicates the presence of interfacial states, and interface recombination is the dominant transport mechanism. The type-II NiO/Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> HJ provides favorable energetics for facile separation and transportation of photogenerated electrons and holes, which is important for all-oxide devices that require bipolar operation and power devices with higher conversion efficiencies.