Effect of film thickness and bottom electrode material on the ferroelectric and photovoltaic properties of sputtered polycrystalline BiFeO3 films

• High-quality polycrystalline BiFeO3 films have been of great interest for many electrical and optical applications, however the fabrication of polycrystalline BFO films offering a large remnant polarization and low leakage current are difficult. In this work, high quality polycrystalline BFO films were deposited using a simplified sputtering method. This is a considerable oversight, as ITO-coated glass is one of the most widely used substrates in industry, and sputtering technique is easily scaled up for mass production. By comparing the measurement results against those obtained with BFO films on FTO/glass and Pt/Ti/SiO2/Si substrates, it is found that choice of electrode material significantly affects the quality of the film. As a result, we found that ITO/glass substrate is more suitable for depositing high quality BFO films.
• The remnant polarization and leakage current density of the poly-BFO films we made are comparable to those epitaxially grown on single crystalline substrates or deposited on Pt buffered Si substrates by pulsed laser deposition.
• There have as yet been few studies pertaining to the ferroelectric properties of BFO films thinner than 240 nm, which can be achieved on an ITO substrate by sputtering. Moreover, there is still little understanding of the relationship between photovoltaic effect and ferroelectric properties of ultrathin BFO film with different thickness. We found that film quality was highly dependent on the film thickness, with a thinner film displaying greater leakage. Despite the degradation in ferroelectric performance, however, the photovoltaic response was enhanced due to an enhanced depolarization field and shortened migration distance. Ultrathin BFO films therefore broaden the potential applications for ferroelectric photovoltaic devices by improving their carrier mobility, and allow for fine-tuning of their band structure when combined with semiconductors and electrodes.

High-quality polycrystalline BiFeO3 (BFO) films have been of great interest for many electrical and optical applications, however the fabrication of polycrystalline BFO films offering a large remnant polarization and low leakage current are difficult. In this work, polycrystalline BFO films were deposited using a radio frequency magnetron sputtering method. It was found that the remnant polarization of BFO deposited on ITO is about three and seventy times larger than films deposited on Pt and FTO, respectively. Film quality was highly dependent on the film thickness, with a thinner film displaying greater leakage. Despite the degradation in ferroelectric performance, however, the photovoltaic response was enhanced. Ultrathin BFO films therefore broaden the potential applications for ferroelectric photovoltaic devices by improving their carrier mobility, and allow for fine-tuning of their band structure when combined with semiconductors and electrodes.