Highly sensitive metal-insulator-semiconductor UV photodetectors based on ZnO/SiO2 core-shell nanowires

Highly sensitive metal-insulator-semiconductor (MIS) UV photodetectors are demonstrated based on ZnO/SiO2 core-shell nanowires. The MIS devices possess simplicity in material synthesis, technological advantages in the device design and uniqueness in the prevailing mechanism. We propose that inserting an insulating SiO2 layer between the metal and photoconductive semiconductor could significantly reduce the dark current resulting in a very high photocurrent to dark current ratio. The photoconductive MIS devices showed a remarkably high photocurrent immediate decay (similar to 99.9%), photo/dark current ratio (similar to 4-5 orders), and photoresponse speed (<100 ms). Furthermore the optical emission properties of ZnO core-shell nanowires are tuned by controlling the dimensions of the ZnO core or the SiO2 shell. The mechanism for this enhanced photoconductivity is suggested to occur by photo-excited electron-hole generation and it's tunnelling through the insulating layer by electron hopping through multiple defect energy states of the SiO2 shell resulting in a large increase of electron-hole pairs. The exploitation of this device structure and material synthesis in other photoconductive nanostructures or insulators with similar traits could result in the low cost fabrication of highly sensitive photodetectors and switches.