Theoretical dissection of the electronic anisotropy and quantum transport of ultrascaled halogenated borophene MOSFETs

Two-dimensional (2D) anisotropic semiconductors, such as black phosphorene, show strong potential in ultrascaled metal-oxide-semiconductor field-effect transistors (MOSFETs) as the anisotropic electronic structure is highly beneficial in boosting the device performance at sub-10-nm gate length regime. Metallic graphenelike borophene can be halogenated to form a stable monolayer family of $B_4{X}_4$ ($X$ = $F,\mathrm{Cl},\mathrm{and}\mathrm{Br}$) whose highly anisotropic semiconducting electronic structures suggest a potential in ultrascaled MOSFET applications. Here, we computationally explore the quantum transport properties of $B_4{X}_4$ monolayers as high-performance (HP) 5-nm MOSFETs. The HP on-state current of the n-type 5-nm monolayer $B_4{X}_4$ MOSFETs can reach over 3000 µA/µm at 5-nm gate length regime, thus fulfilling the ITRS requirement of HP devices. Of note, by analyzing the physical relationship between the anisotropic electronic structures (transport effective mass $m_{//}$ and density of states $m_{\mathrm{DOS}}$), we show that large electronic anisotropy does not immediately guarantee high performance. An overly large $m_{//}$ or $m_{\mathrm{DOS}}$ would suppress the saturation current and lead to limited HP on-state current of monolayer $B_4{X}_4$, thus revealing a balance between the effective masses is needed when designing 2D semiconductor MOSFETs. This work provides insights and design guidelines for the development of next-generation nanoelectronic devices based on the exceptional transport properties of 2D anisotropic channel materials.