Piezotronic and piezo-phototronic effects of atomically-thin ZnO nanosheets

Piezotronic and piezo-phototronic effects have attracted much attention as promising approaches for active electronic/optoelectronic devices. However, the piezotronic and piezo-phototronic devices in previous reports are mainly based on nanowires or two-dimensional transition-metal dichalcogenides that have size of several micrometers along the polarization direction. As the fast development of nanoelectronics and nanooptoelectronics, exploring the piezotronic effect and piezo-phototronic effect at nanometer scale for ultrathin nanodevices and nanosystems is valuable. Here, we investigated the piezotronic and piezo-phototronic effects of atomically thin ZnO nanosheet, and revealed the dominant mechanism. Experiments were performed on the atomically thin ZnO field effect transistor, which showed enhanced electronic transport characteristic under pressure. Theoretical analysis revealed that the change of electronic transport behavior was caused by pressure induced modulation on the effective thickness of the transport channel and the Schottky barrier between ZnO and contact electrodes. Meanwhile, the atomically-thin ZnO film exhibited enhanced response to ultraviolet light under pressure with a high photoresponsivity of 300 AW-1 (Vds = 2 V). This value was improved 230% than the response of the same device under strain-free condition, and more than 103 times higher than the performance of commercial ultraviolet photodetectors, indicating the effectiveness of piezo-phototronic effect in nanoscale. This study shows great promises of the ultrathin devices based on piezotronic and piezo-phototronic effects, which paves the way for atomically-thin semiconductors with out-of-plane piezoelectricity for applications in novel electronics/optoelectronics.