Enhanced Photoresponsivity by Metal Microisland in ZnO Thin Film Based UV Photodetector

Abstract

Ultraviolet photodetectivity in ZnO thin films deposited by sol-gel technique based metal-semiconductor-metal (MSM) photodetectors is investigated. Effect of optical power level of UV radiation and bias voltages on the photoresponse behavior is studied. A two different photodetector configuration comprising, ZnO thin film embedded with microisland metals like Al and Ni were designed and tested. Photoresponsivity was found to be better for the Ni microslands embedded ZnO film as compared to those using Al microisland embedded ZnO thin films. The devices exhibited maximum photoresposivity at 150μW above this value the devices attend to saturate. Ni/ZnO embedded Ni microislands sample exhibits highest quantum efficiency of 214% whereas Al/ZnO embedded Al microislands sample structure presents highest sensitivity of 94%. Devices based on Ni microislands embedded films exhibited gain compared to Al microislands embedded films. Enhancement in the quantum efficiency of Ni/ZnO embedded Ni microisland is attributed to the devices have higher responsivity due to the difference in work function and oxygen affinity values of Ni with the ZnO thin film layer. The study also revealed that the all devices showed a maximum photo-response at flat band voltages of MSMs.