Transport in disordered monolayer MoS₂nanoflakes—evidence for inhomogeneous charge transport

Abstract

We study charge transport in a monolayer MoS2 nanoflake over a wide range of carrier density, temperature and electric bias. We find that the transport is best described by a percolating picture in which the disorder breaks translational invariance, breaking the system up into a series of puddles, rather than previous pictures in which the disorder is treated as homogeneous and uniform. Our work provides insight to a unified picture of charge transport in monolayer MoS2 nanoflakes and contributes to the development of next-generation MoS2-based devices.

Extrinsic Origin of Persistent Photoconductivity in Monolayer MoS2 Field Effect Transistors

“…Figure 5a is an Arrhenius plot of the conductance of sample C at different values and shows that insulating behavior ( dG/dT > 0 ) was found over the temperature range 80 < T < 300 K. For T > 200 K, the MoS 2 sample exhibited thermally activated behavior, where the activation energy was extracted from the linear fit ( E a = 98 meV at V G = 0 V). The carrier transport in this temperature regime could be described by a percolation model, in which conduction occurs via a network of spatially distributed charge puddles 60 . The activation energy then corresponded to the average potential barrier of the charge puddles.…”

High thermoelectric power factor in two-dimensional crystals ofMoS2

“…6(a) where T IMT is plotted as a function of the carrier concentration. Since this phase diagram is linked to percolation, in the insulating phase, the conductivity follows a relation in temperature given by: σ exp(−(T 0 /T) 1/3 ) in a 2D system, which fits a Mott Variable-Range-Hopping (m-VRH) model [16,28,29], separate from the first order transition described elsewhere [14,30]. Figure 6(b) shows the measured Seebeck coefficient, which follows a monotonic increase with temperature as S T 1/3 , using Zyvagin's formula for the m-VRH model [31][32][33], with S→0 as T→0 (inset).…”

Percolative switching in transition metal dichalcogenide field-effect transistors at room temperature

“…A wide variety of physical phenomena ranging from variable range hopping [5], metal-insulator transition [7] to classical percolative charge flow through inhomogeneous medium [21,22] were reported for MoS 2 , the implications of which often lead to a conflicting microscopic scenario. At low carrier density, for example, hopping via single particle states trapped at short-range background potential fluctuations (∼few lattice constants [23]) is incompatible to the observation of classical percolative conduction that requires long-range inhomogeneity in charge distribution, created when linear screening of the underlying charge disorder breaks down [24][25][26][27].…”

“…At low carrier density, for example, hopping via single particle states trapped at short-range background potential fluctuations (∼few lattice constants [23]) is incompatible to the observation of classical percolative conduction that requires long-range inhomogeneity in charge distribution, created when linear screening of the underlying charge disorder breaks down [24][25][26][27]. Observations of metal-insulator transition [7,22] [21,24,25,[40][41][42][43][44], but the experimental difficulty lies in accurately determining the fraction p of the conducting region, or "puddles", embedded inside the insulating matrix. Hence despite compelling evidence of long range inhomogeneity in the charge distribution in MoS 2 FETs [21,22], its manifestation in transport remains indirect and confined only to low temperatures.…”

“…Switching by percolation transition within the "island-and-sea" description in Fig. 3e, has been reported in several different classes of low-dimensional systems, including dilute 2D electron or hole gases in high mobility semiconductor heterostructures [24,25,60,61], silicon inversion layers [26], perovskite oxides [62], graphene nanoribbons [27,63], or even MoS 2 [21,22] and WS 2 [37] FET devices. However the signatures of percolative transport in these systems are usually indirect, and depend on the observation of metal-insulator transition [24,25], or characteristic I sd − V sd scaling [64,65], which can also be limited to low temperatures and/or suffer from nonequilibrium effects.…”