Introduction of built-in electric fields induced by oxygen vacancy gradient distribution to drive high-performance BiFeO₃-based self-powered photodetectors

Due to the unique ferroelectric photovoltaic properties, Bismuth Ferrite (BiFeO₃) is an ideal candidate for miniaturized and high-integration self-powered photodetectors. In this study, a new device structure was designed and constructed using (La, Ni)-gradient-doped BiFeO₃ multi-layers film for achieving a high-performance self-powered photodetector. For instance, such a photodetector achieved a responsivity of 18.7 mA/W and a detectivity of 9.12 × 10⁸ Jones, whose performance is 2 to 4 times those of devices without a gradient structure. An underlying mechanism was proposed that the gradient doping introduced a spatial gradient of oxygen vacancies and lattice in the multilayers film, which in turn generated two novel gradient electric fields (oxygen vacancy gradient field and flexoelectric field). The coupling of these built-in electric fields significantly facilitated the separation of photogenerated carriers and thus enhanced the photocurrent density, which greatly improved the photovoltaic and photoresponse performance of photodetector.