Epitaxial growth of hexagonal boron nitride by metal-organic chemical vapor deposition and its application in memory devices

Abstract

This dissertation presents wafer-scale and selective-area epitaxial growth of hexagonal boron nitride (h-BN) by metal-organic chemical vapor deposition (MOCVD) and explores the potential of h-BN as an active component in memory devices based on in-depth investigation of defects and interfacial charge transfer properties of h-BN. In the first part of this dissertation, wafer-scale epitaxial growth of high-quality h-BN film on Ni(111) template using MOCVD is demonstrated. Compared with inert sapphire substrate, the catalytic Ni(111) template facilitates a fast growth of high-quality h-BN film at the relatively low temperature of 1000 °C. Wafer-scale growth of a high-quality h-BN film with Raman E2g peak full width at half maximum (FWHM) of 18~24 cm−1 is achieved, which is to the extent of our knowledge the best reported for MOCVD. Systematic investigation of the microstructural and chemical characteristics of the MOCVD-grown h-BN films reveals a substantial difference in catalytic capability between the Ni(111) and sapphire surfaces that enables the selective-area growth of h-BN at pre-defined locations over a whole 2-inch wafer. These achievement and findings have advanced our understanding of the growth mechanism of h-BN by MOCVD and will contribute an important step toward scalable and controllable production of high-quality h-BN films for practical integrated two-dimensional (2D) materials-based systems and devices. The second part of this dissertation is devoted to the investigation of resistive switching (RS) behavior of few-layer h-BN mediated by defects and interfacial charge transfer to explore the potential of h-BN as an active component in 2D resistive random access memory (RRAM) applications. Few-layer h-BN is grown on sapphire by MOCVD and used as active RS medium in Ti/h-BN/Au structure, exhibiting clear bipolar RS characteristics without an initial electroforming process. Systematic investigation on microstructural and chemical characteristics of the h-BN reveals that there are structural defects such as homoelemental B−B bonds at grain boundaries and nitrogen vacancies, which can provide preferential pathways for the penetration of Tix+ ions through the h-BN film. In addition, the interfacial charge transfer from Ti to the h-BN is observed by in situ X-ray photoelectron spectroscopy. We suggest that the attractive Coulomb interaction between positively charged Tix+ ions and the negatively charged h-BN surface as a result of the interfacial charge transfer facilitates the migration of Tix+ ions at the Ti/h-BN interface, leading to facile formation of conductive filaments. We believe these findings can improve our understanding of the fundamental mechanisms involved in RS behavior of h-BN and contribute a significant step for the future development of h-BN-based nonvolatile memory applications.