Path of the current flow at the metal contacts of graphene field-effect transistors with distorted transfer characteristics

Nouchi, Ryo; Tanigaki, Katsumi

doi:10.1063/1.4891428

“…Some reports attribute the inflection point to the interface layer between graphene and the metal electrode. [17][18][19] However, the present results demonstrate that the giant Dirac point shift and formation of the inflection point only occur for the n-doped Si substrate, and that they can be attributed to the substrate current. The sweep rate dependence of the phototransistors was measured to investigate the effect of the substrate current in detail.…”

Section: Measurementmentioning

confidence: 51%

“…The electrical properties of the graphene are significantly influenced by its surrounding environment, e.g., the atmosphere, molecules adsorbed on the SiO 2 layer underneath the graphene, [14][15][16] and the oxide interlayer between the metal electrode and graphene. [17][18][19] For instance, water (H 2 O) molecules adsorbed on the graphene surface cause hysteresis in the electrical properties of the transistor. 15 Additionally, the oxide interlayer between the graphene and the metal electrode creates a change in the contact resistance, which produces an additional Dirac point.…”

Section: Introductionmentioning

confidence: 99%

Giant Dirac point shift of graphene phototransistors by doped silicon substrate current

Shimatani

¹

,

Ogawa

²

,

Fujisawa

³

et al. 2016

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Graphene is a promising new material for photodetectors due to its excellent optical properties and high-speed response. However, graphene-based phototransistors have low responsivity due to the weak light absorption of graphene. We have observed a giant Dirac point shift upon white light illumination in graphene-based phototransistors with n-doped Si substrates, but not those with p-doped substrates. The source-drain current and substrate current were investigated with and without illumination for both p-type and n-type Si substrates. The decay time of the drain-source current indicates that the Si substrate, SiO2 layer, and metal electrode comprise a metal-oxide-semiconductor (MOS) capacitor due to the presence of defects at the interface between the Si substrate and SiO2 layer. The difference in the diffusion time of the intrinsic major carriers (electrons) and the photogenerated electron-hole pairs to the depletion layer delays the application of the gate voltage to the graphene channel. Therefore, the giant Dirac point shift is attributed to the n-type Si substrate current. This phenomenon can be exploited to realize high-performance graphene-based phototransistors.

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“…We note that the resulting 1 = 4.2 μm is comparable to the diffusion length of 4 μm obtained from the AFM images (Figure 1b), indicating that the interfacial oxidation occurs approximately in the diffused area. The depinning enables large-area modification of the carrier density, 26,27 which causes a doped graphene region. 28 We therefore conclude that chargedensity depinning and the doping effect occur in the diffusion region, leading to a graphene p-n-p structure.…”

mentioning

confidence: 99%

“…The agreement between the modeled and the measured − curve suggests that the interfacial metal is oxidized. 27 In the calculation, we applied the device geometry with 0 ⁄ = 1.06 and assumed 1 = 0.35 0 ( 0 = 12 μm). We note that the resulting 1 = 4.2 μm is comparable to the diffusion length of 4 μm obtained from the AFM images (Figure 1b), indicating that the interfacial oxidation occurs approximately in the diffused area.…”

mentioning

confidence: 99%

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Observation of quantum Hall plateau-plateau transition and scaling behavior of the zeroth Landau level in graphenep−n−pjunctions

Liu

¹

,

Wang

²

,

Woo

³

et al. 2016

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We report distinctive magnetotransport properties of a graphene p-n-p junction prepared by controlled diffusion of metallic contacts. In most cases, materials deposited on a graphene surface introduce substantial carrier scattering, which greatly reduces the high mobility of intrinsic graphene. However, we show that an oxide layer only weakly perturbs the carrier transport, which enables fabrication of a high-quality graphene p-n-p junction through a one-step and resist-free method. The measured conductance-gate voltage ( − ) curves can be well described by a metal contact model, which confirms the charge density depinning due to the oxide layer. The graphene p-n-p junction samples exhibit pronounced quantum Hall effect, a well-defined transition point of the zeroth Landau level (LL), and scaling behavior. The scaling exponent obtained from the evolution of the zeroth LL width as a function of temperature exhibits a relatively low value of κ = 0.21 ± 0.01.Moreover, we calculate the energy level for the LLs based on the distribution of plateauplateau transition points, further validating the assignment of the LL index of the QH plateau-plateau transition. KeywordsGraphene p-n-p junction, quantum Hall effect, plateau-plateau transition, scaling behavior, while that of the zeroth LL is temperature (T) independent. 13 In a Corbino geometry, FWHM Δν of the zeroth LL is T dependent and shows scaling behavior with κ = 0.16, which is attributed to an inhomogeneous charge carrier distribution. 19 However, until now, a well-defined QH plateau-plateau transition point of the zeroth LL of graphene has not been directly observed, obscuring a detailed understanding of the scaling behavior of this unique LL. Moreover, the variation of the T exponent in previous reports suggests the need for further investigation of the scaling behavior of the zeroth LL using different methods for the device structures.In this report, we fabricate a high-quality graphene p-n-p junction, achieved via controlled diffusion of metallic contacts, to explore the QH plateau-plateau transition and 4 scaling behavior of graphene. Interestingly, we observe a well-defined transition point corresponding to the zeroth LL, revealing the scaling behavior and a reduced T exponent.There are additional advantages of utilizing a graphene p-n-p junction to explore the transition region of the QHE. First, the presence of the transition between an integer QH plateau and a QH plateau with a fractional value enables direct access to the transition of the zeroth LL. Second, in a graphene p-n-p geometry, the intrinsic graphene is adjoined by the doped graphene from both sides. The doped graphene regions can be viewed as an ideal contact, facilitating the investigation of the transition region of the intrinsic graphene.Moreover, we derive the value of energy level for the observed LLs, which agrees with the theoretical values, further validating the assignment of the LL index of the QH plateauplateau transition.A detailed device fabrication process can be found i...

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Observation of Quantum Hall Plateau-Plateau Transition and Scaling Behavior of the Zeroth Landau Level in Graphene p-n-p Junction

Liu¹

2018

Springer Theses

0

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We report distinctive magnetotransport properties of a graphene p-n-p junction prepared by controlled diffusion of metallic contacts. In most cases, materials deposited on a graphene surface introduce substantial carrier scattering, which greatly reduces the high mobility of intrinsic graphene. However, we show that an oxide layer only weakly perturbs the carrier transport, which enables fabrication of a high-quality graphene p-n-p junction through a one-step and resist-free method. The measured conductance-gate voltage ( − ) curves can be well described by a metal contact model, which confirms the charge density depinning due to the oxide layer. The graphene p-n-p junction samples exhibit pronounced quantum Hall effect, a well-defined transition point of the zeroth Landau level (LL), and scaling behavior. The scaling exponent obtained from the evolution of the zeroth LL width as a function of temperature exhibits a relatively low value of κ = 0.21 ± 0.01.Moreover, we calculate the energy level for the LLs based on the distribution of plateauplateau transition points, further validating the assignment of the LL index of the QH plateau-plateau transition.

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Path of the current flow at the metal contacts of graphene field-effect transistors with distorted transfer characteristics

Cited by 10 publications

References 27 publications

Giant Dirac point shift of graphene phototransistors by doped silicon substrate current

Giant Dirac point shift of graphene phototransistors by doped silicon substrate current

Observation of quantum Hall plateau-plateau transition and scaling behavior of the zeroth Landau level in graphenep−n−pjunctions

Observation of Quantum Hall Plateau-Plateau Transition and Scaling Behavior of the Zeroth Landau Level in Graphene p-n-p Junction

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