Role of p-NiO electron blocking layers in fabrication of (P-N):ZnO/Al:ZnO UV photodiodes

• ZnO-based UV photodiodes with p-NiO as an intermediate electron blocking layer (EBL) is fabricated.
• The current density-voltage (J-V) and UV photoresponse properties are investigated.
• The fabricated photodiodes exhibit high UV- photoresponsivity (R) value of 5.53 A/W.
• The response and recovery time under UV illumination is found to be 8.45 s and 10.8 s respectively.

We report the fabrication and characterization of ZnO-based UV photodiodes with p-NiO as an intermediate electron blocking layer (EBL). The n-ZnO and p-ZnO layers are deposited by automated spray pyrolysis technique and NiO layers by r.f.magnetron sputtering. For the realization of p-ZnO, dual acceptor method has been adopted by doping equimolar concentration of group-V elements P and N (0.75 at%) simultaneously in ZnO. The formation of p-type characteristics in ZnO is confirmed by Hall measurement and X-ray photoelectron spectroscopy (XPS) analysis. The n-ZnO is doped with Al (3 at%) in order to improve the electrical properties. The properties of sputtered NiO layers have been investigated under three different deposition temperatures of 300 °C, 350 °C and 400 °C. By analyzing structural and electrical properties, it is revealed that NiO deposited at 350 °C possess better crystallinity and electrical properties. The optimum p-ZnO and n-ZnO layers are stacked upon ITO substrates to form ZnO-based p-n junctions. The effect of addition of NiO as an electron blocking layer (EBL) between the p-n junctions is investigated by analyzing the current density-voltage (J-V) and UV photoresponse properties. The fabricated ZnO-based UV photodiodes with NiO EBL exhibits a high photoresponsivity (R) value of 5.53 A/W with external quantum efficiency (EQE) value of 1.87 × 103%.

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