Fabrication of a p-Ni0.8Cu0.2WO4/n-Si heterojunction diode and its 1 MHz rectifier operation†

Herein, we report on the fabrication of a heterostructure diode adopting a p-Ni_0.8Cu_0.2WO₄ oxide/n-Si junction and its demonstration toward a high-speed rectifier circuit up to 1 MHz operation. Novel p-type Cu-substituted NiWO₄ was synthesized via a solid-state reaction, and its thin-film form was successfully deposited using an e-beam evaporation method. From X-ray diffraction and Raman spectroscopy results, it was confirmed that all the deposited Cu-substituted NiWO₄ films exhibited amorphous phases, irrespective of the substrate heating temperature. UV-visible transmittance and electrical resistivity values decreased as substrate heating temperature was increased from 100 to 300 °C, revealing that optical transparency and electrical conductivity were in a trade-off relation in the Cu-substituted NiWO₄ film. Upon fabricating the p-Ni_0.8Cu_0.2WO₄/n-Si heterostructure diode, a highly rectifying behaviour was attained with an ideality factor of 1.23 and an on/off current ratio of ∼10⁴. When we configured an AC to DC converting half-wave rectifier circuit with the p-Ni_0.8Cu_0.2WO₄/n-Si diode, a high-speed operation up to 1 MHz was demonstrated, thereby strongly supporting that our newly developed p-type oxide can be utilized as a key component in practical oxide-based electronics such as radio frequency identification.