Flexible Difunctional (Pressure and Light) Sensors Based on ZnO Nanowires/Graphene Heterostructures

The piezotronic and piezo-phototronic effects have been extensively utilized in the third-generation semiconductors, such as ZnO, CdS, and GaN, to enhance the performances of electronic and optoelectronic devices. Using the principle of these two effects, here, a flexible difunctional sensor based on graphene/ZnO nanowire array, which can be used to detect vertical pressure as well as ultraviolet light power, is presented. This device shows a linear response to vertical pressures by measuring the change of current, and a pressure sensitivity of 1.7 nA kPa(-1) for smaller pressures. It can also be used to measure the bending strain applied on the substrate. A uniform photoresponsivity of 3.5 mu A W-1 for a 325 nm laser excitation is obtained, and the response speeds for light on- and off-states are 28 and 25 ms, respectively, revealing excellent photoelectric property of this device. These nanowires/graphene heterostructures are flexible with low cost and easy fabrication processes, making it potential in applications of wearable electronic and optoelectronic devices.