High-speed photoresponse properties of ultraviolet (UV) photodiodes using vertically aligned Al:ZnO nanowires

Abstract

Ultraviolet (UV) photodiodes with fast photoresponse properties were fabricated using vertically aligned aluminum doped ZnO nanowires. Stable p-type ZnO have been achieved by doping equimolar concentration of P-N (0.75 at.%) simultaneously in ZnO. The vertically aligned and electrically conducting n-type Al (3 at.%) doped ZnO nanowires were grown by a simple aqueous chemical growth process. The structural, morphological, optical, and electrical properties were investigated. For the fabrication of UV photodiodes, the optimum p-type ZnO layers and n-type ZnO nanowires were stacked upon ITO substrate. A 250 nm thin NiO was deposited as an electron blocking layer (EBL) in between the ZnO p–n junctions. The current density–voltage (J–V) characteristic of the fabricated UV photodiode was measured under dark and UV illumination conditions. Under a reverse bias of 3 V, the device exhibits a high photoresponsivity (R) value of 15.07 (A/W) upon illumination of UV light (λ = 365 nm). The fabricated photodiode exhibits a fast photoresponse switching characteristics with a response and recovery time calculated as 61 ± 11 and 455 ± 41 ms, respectively. The role of vertically aligned nanowires in the formation of oxygen interstitial (Oi) defects and its impact on improving the UV photoresponse properties were investigated.