Abstract
Nanodevices based on monolayer black phosphorus or phosphorene are promising for future electron devices in high density integrated circuits. We investigate bandstructure and size-scaling effects in the electronic and transport properties of phosphorene nanoribbons (PNRs) and the performance of ultra-scaled PNR field-effect transistors (FETs) using advanced theoretical and computational approaches. Material and device properties are obtained by non-equilibrium Green’s function (NEGF) formalism combined with a novel tight-binding (TB) model fitted on ab initio density-functional theory (DFT) calculations. We report significant changes in the dispersion, number, and configuration of electronic subbands, density of states, and transmission of PNRs with nanoribbon width (W) downscaling. In addition, the performance of PNR FETs with 15 nm-long channels are self-consistently assessed by exploring the behavior of charge density, quantum capacitance, and average charge velocity in the channel. The dominant consequence of W downscaling is the decrease of charge velocity, which in turn deteriorates the ON-state current in PNR FETs with narrower nanoribbon channels. Nevertheless, we find optimum nanodevices with W > 1.4 nm that meet the requirements set by the semiconductor industry for the “3 nm” technology generation, which illustrates the importance of properly accounting bandstructure effects that occur in sub-5 nm-wide PNRs.
Highlights
Monolayer black phosphorus (BP) or phosphorene, illustrated in Figure 1a,b, is a promising two-dimensional (2D) material for the realization of future electron devices in integrated circuits due to its favorable electronic and transport properties, which include acceptable bandgap and carrier mobility [1,2]
For a proper assessment of these nanostructured phosphorene field-effect transistors (FETs), methodology must be based on advanced theoretical formalisms such as quantum transport, e.g., nonequilibrium Green’s function (NEGF) formalism, because the transport physics in nanodevices is governed by quantum effects [13,14,15]
We observe that the density-functional theory (DFT)-TB Hamiltonian results in multi-valley bandstructure in both the conduction and valence band, which agrees with DFT studies of ultra-narrow phosphorene nanoribbons (PNRs) reported in [23,38]
Summary
Monolayer black phosphorus (BP) or phosphorene, illustrated in Figure 1a,b, is a promising two-dimensional (2D) material for the realization of future electron devices in integrated circuits due to its favorable electronic and transport properties, which include acceptable bandgap and carrier mobility [1,2]. For a proper assessment of these nanostructured phosphorene FETs, methodology must be based on advanced theoretical formalisms such as quantum transport, e.g., nonequilibrium Green’s function (NEGF) formalism, because the transport physics in nanodevices is governed by quantum effects [13,14,15]. These nanostructures must be described by proper atomically-resolved Hamiltonians that consider the complex bandstructure of such materials at the nanoscale [16,17]. In comparison to DFT results [23], the TBL model does not reproduce the intricate multi-valley bandstructure of PNRs with the widths under ~5 nm
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