2D $\mathbf{B}{\mathbf{e}}_3{\mathbf{B}}_2{\mathbf{C}}_3$:a stable direct-bandgap semiconductor with record-breaking carrier mobility, $8.1\times 10^5\mathbf{c}{\mathbf{m}}^2{\mathbf{V}}^{-1}{\mathbf{s}}^{-1}$

Abstract

The Moore's law in the semiconducting industry has faltered as the three-dimensional (3D) Si-based transistors has approached their physical limit with the downscaling. The carrier mobility $\mu$, critical to the device's performance, will be degraded when the thickness of Si is scaled into several nanometers. In contrast to the bulk counterpart, two-dimensional (2D) semiconductors can be scaled into atomic-layer thickness without dangling bonds, maintaining its intrinsic carrier mobility and going beyond the limits of Si-based electronics. Hence, the development of novel 2D semiconducting materials with high carrier mobility is the market demand as well as the scientific challenge. Here, we successfully designed 2D $\mathrm{B}{\mathrm{e}}_3{\mathrm{B}}_2{\mathrm{C}}_3$ with planar hypercoordinate motif. It possesses the perfect planar skeleton with both pentacoordinate carbon and hexacoordinate boron moieties, which is the first reported material with such multi-hypercoordinate centers. Density functional theory (DFT) calculations prove that the $\mathrm{B}{\mathrm{e}}_3{\mathrm{B}}_2{\mathrm{C}}_3$ monolayer has excellent structural and thermal stabilities as well as mechanical properties. Further investigations reveal that the $\mathrm{B}{\mathrm{e}}_3{\mathrm{B}}_2{\mathrm{C}}_3$ monolayer has a strong ultrahigh Fermi velocity ($2.7\times 10^{5}m/s$), suitable direct bandgap (1.97 eV), and high optical absorption coefficient ($10^5$). As a result, an unprecedented ultrahigh room-temperature carrier mobility ($8.1\times 10^5\mathrm{c}{\mathrm{m}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$) with strong anisotropy is discovered, making $\mathrm{B}{\mathrm{e}}_3{\mathrm{B}}_2{\mathrm{C}}_3$ monolayer a revolutionary candidate for future electronic and photovoltaic applications.

16 pages, 4 figures, 1 table