Tunable Electrical and Optical Properties of Nickel Oxide (NiOx) Thin Films for Fully Transparent NiOx–Ga₂O₃ p–n Junction Diodes

One of the major limitations of oxide semiconductors technology is the lack of proper p-type materials to enable devices such as pn junctions, light-emitting diodes, and photodetectors. This limitation has resulted in an increased research focus on these materials. In this work, p-type NiO x thin films with tunable optical and electrical properties as well as its dependence with oxygen pressure during pulsed laser deposition are demonstrated. The control of NiO x films resistivity ranged from ∼10⁹ to ∼10² Ω cm, showing a p-type behavior with Eg tuning from 3.4 to 3.9 eV. Chemical composition and the resulting band diagrams are also discussed. The all-oxide NiO x-Ga₂O₃ pn junction showed very low leakage current, an ideality factor of ∼2, 10⁵ on/off ratio, and 0.6 V built-in potential. Its J- V temperature dependence is also analyzed. C- V measurements demonstrate diodes with a carrier concentration of 10¹⁵ cm⁻³ for the Ga₂O₃ layer, which is fully depleted. These results show a stable, promising diode, attractive for future photoelectronic devices.