Photoresponse of solution-processed transparent heterojunction ultraviolet photodetectors composed of n-type ZTO and p-type NiO-based semiconductor thin films

The n-type zinc-tin oxide (ZTO) and p-type nickel oxide (NiO) semiconductor thin films were prepared by the sol -gel spin coating process. The influence of 4 at% Mg and Cu doping on the microstructural, optical, and electrical characteristics of NiO thin films and physical properties of ZTO thin film were investigated. In addition, bi-layered ZTO/NiO thin films were grown onto Corning glasses to develop a visible light transparent p-n heter-ojunction ultraviolet (UV) photodetector. Mg doping slightly enhances the visible transparency and enlarges the optical bandgap energy, while Cu doping decreases the visible transparency and narrows the optical bandgap energy. The electrical properties of NiO sol-gel thin films were improved through Mg and Cu doping. According to the current-voltage (I-V) characteristic curves, the n-ZTO/p-NiO:Mg photodetector had the highest rectifi-cation ratio of 11.7 and on-to-off current ratio of 18.3 at 5 V bias. Under UV illumination, the three kinds of devices all exhibited a self-powered nature, while the Mg-and Cu-doped NiO devices had better photoresponse characteristics than the undoped NiO device. It was found that the Mg-doped NiO devices displayed the best photoconductivity gain and sensitivity, and acceptable response speed and responsivity, with applied reverse bias of 1 V.

Automated summary

In this study, n-type zinc-tin oxide (ZTO) and p-type nickel oxide (NiO) semiconductor thin films were prepared by the sol-gel spin coating process. The effects of 4 at% Mg and Cu doping on the microstructural, optical, and electrical characteristics of NiO thin films, as well as the physical properties of ZTO thin films, were investigated. Furthermore, a bi-layered ZTO/NiO thin film was developed on Corning glasses to create a visible light transparent p-n heterojunction ultraviolet (UV) photodetector. Mg doping improved visible transparency and increased optical bandgap energy, while Cu doping decreased visible transparency and narrowed the optical bandgap energy. The electrical properties of NiO sol-gel thin films were enhanced through Mg and Cu doping. The n-ZTO/p-NiO:Mg photodetector exhibited the highest rectification ratio and on-to-off current ratio. Under UV illumination, all three types of devices displayed self-powered behavior, with the Mg and Cu-doped NiO devices showing better photoresponse characteristics than the undoped NiO device. Mg-doped NiO devices demonstrated the highest photoconductivity gain and sensitivity, as well as acceptable response speed and responsivity, with an applied reverse bias of 1 V.