Charged impurity scattering in top-gated graphene nanostructures

Ong, Zhun-Yong; Fischetti, Massimo V.

doi:10.1103/physrevb.86.121409

Cited by 30 publications

(26 citation statements)

References 18 publications

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“…When Fallahazad and co-workers deposited HfO 2 on SiO 2 -supported SLG, they did not observe any mobility enhancement although they did find that a thinner gate oxide increases the mobility in SLG [16]. This has been explained as consequence of greater screening of the charged impurities by the metal gate [17]. In every instance that we know of [16,[18][19][20][21], the deposition of an oxide layer on high-mobility, non-epitaxial SLG has lead to a mobility decrease, probably as a result of more CI and defect scattering.…”

Section: Introductionmentioning

confidence: 99%

“…However, this means SLM is highly susceptible to the local electrical field generated by charged impurities near or at the substrate surface. Therefore, the electron mobility is expected to be strongly affected by charged impurity (CI) scattering [9] and/or remote phonon scattering [10][11][12][13][14].…”

Section: Introductionmentioning

confidence: 99%

“…[17] and including not only the effect of the dielectric environment but also the temperature dependence of the charge polarizability. HfO 2 -covered SLM on a SiO 2 substrate is used as a model system here although the theory can be easily generalized to other gate dielectrics and single-layer transition metal dichalcogenides (TMDs).…”

Section: Introductionmentioning

confidence: 99%

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Mobility enhancement and temperature dependence in top-gated single-layer MoS2

2013

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The deposition of a high-κ oxide overlayer is known to significantly enhance the room-temperature electron mobility in single-layer MoS2 (SLM) but not in single-layer graphene (SLG). We give a quantitative account of how this mobility enhancement is due to the non-degeneracy of the twodimensional electron gas system in SLM at accessible temperatures. Using our charged impurity scattering model [Ong and Fischetti, Phys. Rev. B 86, 121409 (2012)] and temperature-dependent polarizability, we calculate the charged impurity-limited mobility (µimp) in SLM with and without a high-κ (HfO2) top gate oxide at different electron densities and temperatures. We find that the mobility enhancement is larger at low electron densities and high temperatures because of finite-temperature screening, thus explaining the enhancement of the mobility observed at room temperature. µimp is shown to decrease significantly with increasing temperature, suggesting that the strong temperature dependence of measured mobilities should not be interpreted as being solely due to inelastic scattering with phonons. We also reproduce the recently seen experimental trend in which the temperature scaling exponent (γ) of µimp ∝ T −γ is smaller in top-gated SLM than in bare SLM. Finally, we show that a ∼ 37 percent mobility enhancement can be achieved by reducing the HfO2 thickness from 20 to 2 nm.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Mobility enhancement and temperature dependence in top-gated single-layer MoS2

2013

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“…where n imp is the CI density concentration, and φ(k, k ′ ) is the scattering potential given by [32] …”

Section: Calculation Of Charged Impurity Mobilitymentioning

confidence: 99%

Anisotropic charged impurity-limited carrier mobility in monolayer phosphorene

Ong

Zhang

2014

Journal of Applied Physics

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The room temperature carrier mobility in atomically thin 2D materials is usually far below the intrinsic limit imposed by phonon scattering as a result of scattering by remote charged impurities in its environment. We simulate the charged impurity-limited carrier mobility µ in bare and encapsulated monolayer phosphorene. We find a significant temperature dependence in the carrier mobilities (µ ∝ T −γ ) that results from the temperature variability of the charge screening and varies with the crystal orientation. The anisotropy in the effective mass leads to an anisotropic carrier mobility, with the mobility in the armchair direction about one order of magnitude larger than in the zigzag direction. In particular, this mobility anisotropy is enhanced at low temperatures and high carrier densities. Under encapsulation with a high-κ overlayer, the mobility increases by up to an order of magnitude although its temperature dependence and its anisotropy are reduced.The search for alternatives to graphene for nanoelectronic applications has expanded lately to include transition metal dichalcogenides (TMDs) [1][2][3][4] and other atomically thin two-dimensional (2D) crystals. [5,6] Phosphorene, an ultrathin form of black phosphorus (BP), has recently garnered considerable interest because of its potentially high carrier mobility (∼ 300 cm 2 V −1 s −1 in few-layer samples [7]), direct band gap [8] and electrical conductance anisotropy. [9] In contrast, measurements of unprocessed monolayer TMD crystals have yielded room-temperature mobilities typically below 10 cm 2 V −1 s −1 [10] although the mobility in similarly thick multilayer MoS 2 has been measured to be around 200 cm 2 V −1 s −1 .[11] However, recent experimental studies of the hole mobility in few-layer BP suggest that thinning phosphorene leads to a substantial reduction in the mobility, [8,12] possibly due to the closer proximity between the charge carriers and remote Coulomb impurities in the substrate. Extrapolating to a single phosphorene layer, the carrier mobility would ultimately be limited by charged impurity scattering even at room temperature, as in monolayer MoS 2 . [13] Despite intense theoretical interest in monolayer phosphorene, [14,15] there has not been a successful demonstration of a working monolayer phosphorene-based field-effect transistor (FET) to date.[8] Nonetheless, the eventual realization of such a device is highly probable in our opinion since monolayer phosphorene has been physically isolated [8]. The atomic thinness of a monolayer 2D crystal also allows for higher on-off current ratios, providing superior electrostatic modulation of the channel carrier density via an external gate. In a FET, this results in small off-currents and large switching ratios which are advantageous for low-power device applications. Thus, it would be advantageous to have a model of charge transport in supported monolayer phosphorene that takes into account its anisotropic character and can be used to interpret electrical transport data from realistic phosph...

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“…7 There are several experimental and theoretical studies that have examined the role of ionized impurities on the formation of charge puddles and on charge transport in graphene at low electric fields, on insulating substrates. [8][9][10][11] Researchers have also found they can directly control impurity scattering in graphene by screening it with solvents of high dielectric constant. 12 However, the role of substrate phonons is difficult to quantify directly.…”

Section: Introductionmentioning

confidence: 99%

Theoretical analysis of high-field transport in graphene on a substrate

Serov

Ong

Fischetti

et al. 2014

Journal of Applied Physics

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We investigate transport in graphene supported on various dielectrics (SiO2, BN, Al2O3, HfO2) through a hydrodynamic model which includes self-heating and thermal coupling to the substrate, scattering with ionized impurities, graphene phonons and dynamically screened interfacial plasmonphonon (IPP) modes. We uncover that while low-field transport is largely determined by impurity scattering, high-field transport is defined by scattering with dielectric-induced IPP modes, and a smaller contribution of graphene intrinsic phonons. We also find that lattice heating can lead to negative differential drift velocity (with respect to the electric field), which can be controlled by changing the underlying dielectric thermal properties or thickness. Graphene on BN exhibits the largest highfield drift velocity, while graphene on HfO2 has the lowest one due to strong influence of IPP modes.

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Charged impurity scattering in top-gated graphene nanostructures

Cited by 30 publications

References 18 publications

Mobility enhancement and temperature dependence in top-gated single-layer MoS2

Mobility enhancement and temperature dependence in top-gated single-layer MoS2

Anisotropic charged impurity-limited carrier mobility in monolayer phosphorene

Theoretical analysis of high-field transport in graphene on a substrate

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