Highly Sensitive Switchable Heterojunction Photodiode Based on Epitaxial Bi₂FeCrO₆ Multiferroic Thin Films

Perovskite multiferroic oxides are promising materials for the realization of sensitive and switchable photodiodes because of their favorable band gap (<3.0 eV), high absorption coefficient, and tunable internal ferroelectric (FE) polarization. A high-speed switchable photodiode based on multiferroic Bi₂FeCrO₆ (BFCO)/SrRuO₃ (SRO)-layered heterojunction was fabricated by pulsed laser deposition. The heterojunction photodiode exhibits a large ideality factor ( n = ∼5.0) and a response time as fast as 68 ms, thanks to the effective charge carrier transport and collection at the BFCO/SRO interface. The diode can switch direction when the electric polarization is reversed by an external voltage pulse. The time-resolved photoluminescence decay of the device measured at ∼500 nm demonstrates an ultrafast charge transfer (lifetime = ∼6.4 ns) in BFCO/SRO heteroepitaxial structures. The estimated responsivity value at 500 nm and zero bias is 0.38 mA W^-1, which is so far the highest reported for any FE thin film photodiode. Our work highlights the huge potential for using multiferroic oxides to fabricate highly sensitive and switchable photodiodes.