Ab initio mobility of single-layer MoS₂ and WS₂: comparison to experiments and impact on the device characteristics

Abstract

We combine the linearized Boltzmann Transport Equation (LBTE) and quantum transport by means of the Nonequilibrium Green's Functions (NEGF) to simulate single-layer MoS2 and WS2 ultra-scaled transistors with carrier mobilities extracted from experiments. Electron-phonon, charged impurity, and surface optical phonon scattering are taken into account with all necessary parameters derived from ab initio calculations or measurements, except for the impurity concentration. The LBTE method is used to scale the scattering self-energies of NEGF, which only include local interactions. This ensures an accurate reproduction of the measured mobilities by NEGF. We then perform device simulations and demonstrate that the considered transistors operate far from their performance limit (from 50% for MoS2 to 60% for WS2). Higher quality materials and substrate engineering will be needed to improve the situation.

Toward Low-Temperature Solid-Source Synthesis of Monolayer MoS2

“…13,16,[28][29][30] (Recent simulations have shown mobilities in this range are limited by point defects, most likely charge impurities and sulfur vacancies. 69,70 ) Field-effect mobility (µFE) data reported for 1L MoS2 grown at 850°C (lighter hollow triangles) are also included as a box-andwhisker plot (average µFE of 34.2 cm 2 V -1 s -1 outlined in the black box) 16 in good agreement with the 850°C effective mobility. For CVD-grown 1L MoS2 using solid source precursors, our values are the highest reported mobilities to date with a thermal budget below 2-hours at 600°C.…”

Circuit-aware Device Modeling of Energy-efficient Monolayer WS$_2$ Trench-FinFETs

“…At small mobility values, e.g. 40 cm 2 /Vs, which is the result of charged impurity scattering in WS 2 with an impurity concentration N imp =1.35x10 12 cm −2 [5], the EDP of the WS 2 T-FinFET is 26 % lower than that of the s-Si FinFET for the same delay. The advantage of T-FinFET is about the same (28 % lower EDP) at higher mobility values, i.e.…”

“…Fig. 1(d) shows the transfer characteristics of WS 2 T-FinFET for a fixed FP = 24 nm and H f in = 15 nm, with an intrinsic phonon-limited electron mobility µ = 360 cm 2 /(V•s) [5]. The effective device width can be controlled by changing either the fin height (H f in ) or the extensions of the channel width (W ext ).…”

Impact of Device Scaling on the Electrical Properties of MoS2 Field-effect Transistors

“…This is mainly due to SS degradation observed for short Lch devices, and will be further discussed in Section E. Next, we evaluate the Ion at a fixed charge density (ns) of 10 cm -2 and do not observe any difference between the 50 nm SiO2 and 12 nm HfO2 samples (Fig 2a). This indicates that the carrier transport in the MoS2 channel is predominantly limited by charged impurities 14 in the MoS2 or at the interfaces, and not by remote phonons 15 in the gate oxide.…”