Illumination-dependent free carrier screening effect on the performance evolution of ZnO piezotronic strain sensor

Performance modulation of ZnO optoelectronic devices in the presence of proper piezoelectric polarization charges has been widely reported, whereas relatively less work has been performed about the influence of photoexcitation on piezotronics. In this stud~ we experimentally investigated the performance evolution of ZnO piezotronic strain sensor under various 365 nm UV irradiation densities. The device demonstrated a response ratio of -200 under no illumination and under -0.53% compressive strain, and the response time is approximately 0.3 s. However, tremendous performance degradation was observed with the increase in the illumination densi~, which is attributed to the W-modulated change in the free electron concentration and Schottky barrier height. It was observed that increased carrier density intensifies the screening effect and thus, the modulation ability of piezo-polarization charges weakens. Meanwhile, the deterioration of rectifying behavior at the interface under UV illumination also jeopardizes the device performance.

The coupling influence of UV illumination and strain on the surface potential distribution of a single ZnO micro/nano wire

Interface/surface properties play an important role in the development of most electronic devices. In particular, nanowires possess large surface areas that create new challenges for their optoelectronic applications. Here, we demonstrated that the piezoelectric field and UV laser illumination modulate the surface potential distribution of a bent ZnO wire by the Kelvin probe force microscopy technology. Experiments showed that the surface potential distribution was changed by strain. The difference of surface potential between the outer/inner sides of the ZnO wire increased with increasing strain. Under UV laser illumination, the difference of surface potential between the outer/inner sides of the ZnO wire increased with increasing strain and illumination time. The origin of the observed phenomenon was discussed in terms of the energy band diagram of the bent wire and adsorption/desorption theory. It is suggested that the change of surface potential can be attributed to the uneven distribution of the carrier density across the wire deduced by the piezoelectric effect and surface adsorption/desorption of oxygen ions. This study provides an important insight into the surface and piezoelectric effects on the surface potential and can help optimize the performance of electronic and optoelectronic devices. [Figure not available: see fulltext.] © 2016, Tsinghua University Press and Springer-Verlag Berlin Heidelberg.