a–e 3D Schema of UV Photodetector fabrication using contact printed ZnO and Si NWs. Fabrication steps of UV PDs based on ZnO and Si NWs, comprising: (a) definition of 20 mm2 areas on a S1818 photoresist layer by photolithography, followed by an O2 plasma treatment (100 Watt and 0.3 mbar for 1 min). Contact Printing of (b) Si and (c) ZnO NWs. d removal of the photoresist in warm acetone (50 °C for 2 min). e definition of Ti(4 nm)/Au(200 nm) interdigitated electrodes by photolithography and lift-off, where (e1) and (e2) show SEM images of printed ZnO and Si NWs, respectively, bridging a pair of Ti/Au electrodes with a 5 μm gap. f WB equivalent circuit and the expression determining the electric current flowing through ZnO NWs. g Idark and (h) ΔIdark vs. Temp. for WB and single resistance (SR) UV PDs. i Single cycle and (j) multi-cycles measured over time and using a UV LED power density of 4.5 μW/cm2 and a Vin of 0.05 V, keeping a distance between UV LED and the PD surface of 5 cm. Reprinted with permission from Ref.