Observation of the Photoenhanced Piezoelectric Effect on (101̅0) Orientated ZnO Single Crystal

It is rather expected and challenging to develop an unconventional approach to enhancing piezoelectric properties. Here, we show a conceptually different approach to improve the piezoelectric generation of a ZnO (101̅0) single crystal piezoelectric generator by light illumination. The output current increased from 0.19 ± 0.005 to 0.74 ± 0.02 μA under a 0.171 W/cm2 of ultraviolet (UV) light illumination. This phenomenon is known as the photoenhanced piezoelectric effect. Like the piezoelectric effect, the photoenhanced piezoelectric effect takes place in the polar [0001] direction, whereas no photoenhanced piezoelectric effect is observed in the [12̅10] nonpolar direction. The piezoelectric and photoenhanced piezoelectric effects are evidenced to originate in the spontaneous electric field along the polar azimuth of [0001]. In the piezoelectric and photoenhanced piezoelectric effects, the applied stress induces a transition from the polar superstructure to the nonpolar superstructure, the fettered charge carriers are released, and a piezoelectric current is thus generated. The illumination of UV light increases the number of fettered charges, and thus, the output current is enhanced. This light illumination approach is likely to be applied to improve the properties of other piezoelectric materials. This polar superstructure piezoelectric model is further demonstrated and can be used to guide the design of high-performance piezoelectric materials and devices.