Piezo-phototronic effect enhanced pressure sensor based on ZnO/NiO core/shell nanorods array

Highlights: • The ZnO/NiO piezotronic pressure sensor is fabricated. • The NiO shell acted as a barrier layer for improving sensitivity. • The sensitivity is further enhanced by piezo-phototronic effect. Piezotronic pressure sensors have drawn a lot of attention since the piezotronic theory was established. In this work, a piezotronic pressure sensor based on ZnO/NiO core/shell nanorods array is fabricated by a simple and low-cost method. From the I–V characteristics, we can know that a reliable barrier layer is formed at the ZnO/NiO interface. When the ZnO/NiO nanorods are compressed by the pressure, the piezopotential in ZnO changes the NiO barrier height and then modulate the carrier distribution and transportation. Furthermore, the piezo-phototronic effect is a three-way coupling effect of semiconductor, piezoelectric-polarization and photon-excitation properties, which may be a feasible approach to enhance the performance of pressure sensors by tuning the generation, separation and recombination of photo-generated electron–hole pairs during optoelectronic processes in piezoelectric-semiconductor materials. Here, the performance of the pressure sensors is optimized and significantly enhanced by coupling of the piezoelectric effect and photo-excitation of ZnO nanorods. Under a UV (365 nm) illumination, the enhancement in switch ratio and sensitivity of the pressure sensor is about 353% and 445%, respectively. The enhancement is attributed to weakening the influence of bulk resistance. Thus, ZnO/NiO interface plays a crucial role in determining the electrical transport property. Particularly, the created electrons by photons moved towards and accumulated at the interface, which results that more electrons can tunnel through the barrier layer than that without UV illumination under loading. These results indicate the capability of the piezo-phototronic effect to effectively enhance/optimize the performances of pressure sensors.