Structures and photoelectric properties of superdomains in epitaxial (110)-PZT films

Nano-domains with multiple ferroic orders have received increasing attention for their potential applications in next-generation electronics, including non-volatile memories, sensors, and phototronic devices etc. In this work, we construct a broad picture of ferroelectric properties, photoelectric behaviors, and multiple manipulating pathways on a strained (110)-oriented epitaxial Pb(Zr_xTi_1-x)O₃ (PZT) film. The in-plane strain from SrTiO₃ (110) substrate breaks the uniaxial symmetry of the tetragonal PZT, and with suitable strain energy, superdomains can be formed in local areas. Piezoresponse force microscopy (PFM) and conductive atomic force microscopy (cAFM) are used to determine the three-dimensional polarization orientations of the superdomain structures and reveal the nature of the conductive domain walls. The enhanced photoactivity is shown in the head-to-head charged domain walls, which is due the bandgap reduction led by the band bending effect, and the superdomains exhibit enhanced photoelectrochemical (PEC) performance compared to that of typical c/a domains in PZT. Finally, we utilized time-varying pulsed voltages to measure the dynamic current switching within one millisecond and achieve direct/multi-step switching for different polarization state manipulation. The understanding of the photoelectrical mechanisms and the multiple pathways to control the intermediate state make the superdomain PZT a candidate for functional photoelectronic devices.