Thickness Dependence of Photoconductance in Strained BiFeO3 Thin Films With Planar Device Geometry

Abstract

The recent discovery of efficient charge separation in tetragonal–rhombohedral (T‐R) polymorphic phase boundaries (PPBs) in strained BiFeO3 (BFO) films is of great interest, and also raised a question of whether the PPBs could enhance the performance of BFO‐based planar photodetectors. To address it, we prepare BFO films with thickness ranging from 8 to 90 nm on the LaAlO3 substrates, in which the BFO evolves from a pure T phase (without PPBs) to a T‐R mixed phase (with PPBs) due to the strain relaxation. Then, we comparatively investigate the photoconductive properties of these BFO films with the planar device geometry. It is found that the photoconductance first increases and then decreases with increasing film thickness. Particularly, the 50‐nm film containing the pure T phase without any detectable PPBs exhibits the highest photoconductance. This unexpected observation can be understood by analyzing the effects of increasing film thickness and associated phase evolution on the photoconduction‐related parameters.