Bismuth oxychloride as a <i>van der Waals</i> dielectric for 2D electronics

Two-dimensional (2D) semiconductors have received a lot of attention as the channel material for the next generation of transistors and electronic devices. On the other hand, insulating 2D gate dielectrics, as possible materials for gate dielectrics in transistors, have received little attention. We performed an experimental study on bismuth oxychloride, which is theoretically proposed to have good dielectric properties. High-quality bismuth oxychloride single crystals have been synthesized, and their high single crystallinity and spatial homogeneity have been thoroughly evidenced by x-ray diffraction, Raman spectroscopy, x-ray photoelectron spectroscopy, transmission electron microscopy (TEM), and scanning TEM studies. We then mechanically exfoliated high-quality BiOCl crystals to fabricate metal-insulator-metal (MIM) capacitors and measured the dielectric properties at various frequencies and different thicknesses. We found that BiOCl exhibits an out-of-plane static dielectric constant up to 11.6, which is 3 times higher than 2D hexagonal boron nitride making it a suitable candidate for 2D dielectrics. We also carried out cross-section TEM studies to look into the MIM interface and provide some future directions for their integration with metal-dielectric interfaces and possibly with other 2D devices.