Fabrication and photoresponse of a pn-heterojunction diode composed of transparent oxide semiconductors, p-NiO and n-ZnO

Transparent trilayered oxide films of ZnO/NiO/indium tin oxide were heteroepitaxially grown on a YSZ (111) substrate by pulsed-laser deposition combined with a solid-phase-epitaxy technique, and were processed to fabricate a $\mathrm{p-}\mathrm{NiO}\mathrm{/n-}\mathrm{ZnO}$ diode. The diode exhibited a clear rectifying $\mathrm{I–V}$ characteristic with an ideality factor of ∼2 and a forward threshold voltage of ∼1 V. Although the photoresponsivity was fairly weak at the zero-bias voltage, it was enhanced up to ∼0.3 ${\mathrm{A W}}^{\text{−1}}$ through the application of a reverse bias of −6 V under the irradiation of 360 nm light, a value comparable to that of commercial devices.