Varying load resistances of zinc oxide ultraviolet photodetectors: A simple method to change responsivity

The metal–semiconductor–metal structured ultraviolet photodetector has been fabricated based on Zinc oxide thin films grown by a radio frequency magnetron sputtering technique, and Au is used as the contact metal. The dark current of the photodetector is as low as 1.17 nA at 3 V bias in the current–voltage measurements. The photoresponse properties are characterized by varying the load resistors (1 kΩ, 10 kΩ, 100 kΩ, 1 MΩ and 22 MΩ), and the corresponding responsivities are 2.69, 1.27, 0.25, 0.02 and 7.20×10−4 A/W. It can be found that the responsivity of the photodetector is enhanced with the load resistors decreasing; however, the signal-to-noise ratio decreases. It is demonstrated that the best method to make the ZnO-based photodetector suitable for different application environments is with the appropriate load resistance.