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 ${\mathrm{B}}_{4}{\mathrm{X}}_{4}$ ($\mathrm{X}$ = $\mathrm{F},\phantom{\rule{0.2em}{0ex}}\mathrm{Cl},\phantom{\rule{0.2em}{0ex}}\mathrm{and}\phantom{\rule{0.2em}{0ex}}\mathrm{Br}$) whose highly anisotropic semiconducting electronic structures suggest a potential in ultrascaled MOSFET applications. Here, we computationally explore the quantum transport properties of ${\mathrm{B}}_{4}{\mathrm{X}}_{4}$ monolayers as high-performance (HP) 5-nm MOSFETs. The HP on-state current of the n-type 5-nm monolayer ${\mathrm{B}}_{4}{\mathrm{X}}_{4}$ MOSFETs can reach over 3000 \textmu{}A/\textmu{}m 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 ${\mathrm{B}}_{4}{\mathrm{X}}_{4}$, 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.