Fabrication and Characterization of All-Transparent Li0.15Ni0.85O/In–Mg0.5Zn0.5O Thin-Film p–n Heterojunction Diodes with Cube-on-Cube Epitaxial Structures

All-oxide-based transparent p–n heterojunctions with the cubic epitaxial structure of Pt-electrode/p-Li0.15Ni0.85O (LNO)/n-In–Mg0.5Zn0.5O (In–MZO)/Pt-electrode on LaAlO3 (LAO) (100) substrate were fabricated. The rectification ratio Rc of forward current to reverse current of this heterojunction diode is larger than 60 in the range of applied voltages from -4.0 to +4.0 V. The reverse breakdown voltage is larger than 6 V at temperatures of 30 to 380 K, which confirms the possibility of high-temperature applications. The epitaxial relationships were confirmed to be cube-on-cube epitaxy of (100)LNO ∥ (100)In–MZO ∥ (100)LAO (out-of-plane) and (011)LNO ∥ (011)In–MZO ∥ (010)LAO (in-plane). The measured optical transmission of the heterojunction is 70–80% in the infrared and visible regions. Absorption occurs in the UV region, which corresponds to the band gaps of LNO and In–MZO, suggesting that these heterojunctions formed by transparent LNO and In–MZO films could be used as UV detectors and transparent electronic devices.