Growth and physical properties of BiFeO3 thin films directly on Si substrate

Abstract

Multiferroic BiFeO3 thin films have been widely studied for their intriguing fundamental physics and exotic functional properties. Integration of the BiFeO3 thin films with semiconductor Si is crucial for the practical development of novel electronic and photosensitive devices. Here, we report the fabrication and physical properties of BiFeO3 thin films grown directly on bare Si substrate by laser-molecular beam epitaxy. It was found that a predeposition process performed at room temperature and high vacuum conditions is effective and necessary for obtaining the pure-phase BiFeO3 thin films. X-ray diffraction measurements indicate that the obtained BiFeO3 thin films are in a single-phase polycrystalline state and show improved crystallinity with increasing thickness, and a transmission electronic microscopy image illustrates an interface layer around 3 nm in thickness existing between the BiFeO3 thin films and Si substrate. Electrical measurements show that the BiFeO3 thin films have good ferroelectricity and low leakage current. Moreover, optical properties investigated by spectroscopic ellipsometry demonstrate that the direct band gap of the thin films increases with decreasing thickness.