Boosting the photoresponse speed of visible-light-active bismuth ferrite thin films based on Fe-site substitution strategy and favorable heterostructure design

Although BiFeO3 (BFO) is regarded as one of up-and-coming ferroelectric oxides in the field of semiconducting devices due to its anomalous optoelectronic characteristics, is it possible to exploit its potential in the application of photodetection in visible band (Vis)? To answer this question, we firstly follow the recognized strategy of Fe site substitution by involving zinc ions in BFO, i.e. synthesize BiFe1-xZnxO3 (BFZO) by sol-gel technique and successfully shrink its energy bandgap (E-g) from 2.3 eV of pure BFO down to circa 2.0 eV; moreover, we innovatively integrate hole-transporter NiO and constitute BFZO/NiO heterostructure to further accelerate charge carrier transitions. Going through systematical investigation on E-g and leakage current of BFZO films with Zn ratio optimization, as well as energy band alignment between BFZO and NiO, the splendid photo-response speed of BFZO/NiO heterojunction is achieved. The best response time constants of photocurrent rising and decay are optimized to 0.36 ms and 0.49 ms, which are two order-of-magnitude faster than pure-BFO/NiO and one order-of-magnitude faster than single BFZ(0.8)O film. Such neo-heterojunction has overwhelming photo response properties compared to other congeneric BFO/metal-ion-doped-BFO photodetectors reported elsewhere. Hereby, it portends a promising future of conventional wide-bandgap ferroelectric oxides in the application of up-to-date high-speed Vis detection.