FeVO4-based solution-processed all oxide self-biased fast photodetectors

Abstract

The wide band gap (E_g) nature of the commonly used binary oxides and the energy-intensive vacuum processing of complex oxide thin film deposition limits the low-cost all-oxide self-biased photodetectors (PDs) with the capacity to detect both ultraviolet (UV) and visible light. Here, we report the photo-physical properties of a solution-processed n-type FeVO₄ (FVO) thin film and, for the first time, used it as the absorber material in self-biased photodetection. The spin-coated FVO film on a fluorine-doped tin oxide (FTO) coated glass substrate shows a typical monoclinic structure with a direct E_g of around 2.5–2.8 eV with an absorption coefficient as high as 10⁵ cm⁻¹. Adding a thin layer of p-type wide E_g NiO, we designed an FVO/NiO n–p heterojunction, which is capable of self-biased photodetection for both UV and visible light. The FVO/NiO self-biased PDs show responsivity and detectivity of 18 mA W⁻¹ and 5.3 × 10¹⁰ Jones at a wavelength of 445 nm, respectively, comparable to the oxide-based PDs synthesized by the physical vapour deposition method. The rise and decay time for 90% of their maximum current value is close to 46 ms (instrumentation limit), representing the fast response of our PDs. Our device retains its responsivity for dripping water and drying at a temperature over 120 °C. Furthermore, our device was able to detect light in the measured range from 380 nm to 785 nm, enabling broadband photodetection capacity. The addition of this photosensitivity in commonly known antiferromagnetic oxide FVO not only enhances its multifunctionality but also shows a new direction toward cost-effective, stable, and self-biased PDs.