Understanding the nature of remnant polarization enhancement, coercive voltage offset and time-dependent photocurrent in ferroelectric films irradiated by ultraviolet light

It is widely accepted that ultraviolet (UV) light illumination of ferroelectric films can result in polarization imprint because of the accumulation of photoinduced carriers on the domain walls and/or on the electrode–film interfaces, and then the decrease of the reversible remnant polarization. In this paper, however, the enhancement of remnant polarization was exhibited in Pb(Zr0.2Ti0.8)O3 (PZT) films when irradiated by UV light. The time-dependent photocurrent and hysteresis loop of PZT films indicated that the transient behavior of photocurrent and coercive voltage offset were closely related to the polarization states, moveable defect charge (mainly oxygen vacancy) density, and aging time. Based on the observation of piezoresponse force microscopy, the mechanism behind the observed photoelectric and ferroelectric phenomena was proposed.