Broadband and High-Sensitivity Photodetector Based on BiFeO₃/Si Heterojunction

Photovoltaic devices based on ferroelectric materials have broad application prospects; however, there are also problems of narrow bandwidth and low sensitivity. In this paper, polycrystalline BiFeO3 (BFO) films are prepared directly on n-Si (100) substrates to form ferroelectric/semiconductor heterostructures, the electrical response of which under weak light intensity (0.8 W m(-2)) is systematically investigated. Accompanied by the dielectric relaxation originated from photocarriers, the polarization of BFO increases while the coercive voltage decreases. Especially, current-voltage (I-V) curve under negative bias voltage changes obviously with illumination, and cyclically switchable photocurrent is detected at 0 V bias, with the on-off ratio increasing for lower temperature. Although the photoresponse is detectable in the broad wavelength range of 275-1100 nm, it is more pronounced for visible light. It is considered that the built-in electric field of the PN junction at the BFO/n-Si interface drives the separation and migration of photocarriers, which in turn affects the interface barrier and the distribution of monovalent oxygen vacancies (VO center dot$V_{\rm{O}}<^> \bullet $) in BFO while producing the photovoltaic effect. This work provides an effective route for developing photodetectors with high sensitivity and broadband detection.