Observation of negative contact resistances in graphene field-effect transistors

Nouchi, Ryo; Saito, Tatsuya; Tanigaki, Katsumi

doi:10.1063/1.4705367

Cited by 25 publications

(25 citation statements)

References 23 publications

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“…The DOS of single-layer graphene increases as the Fermi level is shifted away from its charge neutrality point (the so-called Dirac point) [19]. Thus, the CT from the electrode metal increases the DOS of the underlying graphene, leading to a lower contact resistance [20,21]. In the case of BLG, the situation is rather complicated because of its tuneable bandgap.…”

Section: Introductionmentioning

confidence: 99%

Contact resistance at planar metal contacts on bilayer graphene and effects of molecular insertion layers

Nouchi

2017

Nanotechnology

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The possible origins of metal-bilayer graphene (BLG) contact resistance are investigated by taking into consideration the bandgap formed by interfacial charge transfer at the metal contacts.Our results show that a charge injection barrier (Schottky barrier) does not contribute to the contact resistance because the BLG under the contacts is always degenerately doped. We also showed that the contact-doping-induced increase in the density of states (DOS) of BLG under the metal contacts decreases the contact resistance owing to enhanced charge carrier tunnelling at the contacts. The contact doping can be enhanced by inserting molecular dopant layers into the metal contacts. However, carrier tunnelling through the insertion layer increases the contact resistance, and thus, alternative device structures should be employed. Finally, we showed that the inter-band transport by variable range hopping via in-gap states is the largest contributor to contact resistance when the carrier type of the gated channel is opposite to the contact doping carrier type. This indicates that the strategy of contact resistance reduction by the contact-doping-induced increase in the DOS is effective only for a single channel transport branch (n-or p-type) depending on the contact doping carrier type. 2

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Section: Introductionmentioning

confidence: 99%

Contact resistance at planar metal contacts on bilayer graphene and effects of molecular insertion layers

Nouchi

2017

Nanotechnology

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“…Data for short L was excluded from the extrapolation because we consistently observed pronounced deviations from a linear fit to the data at shorter L. This observation is consistent with the reported observed changes in the electrical properties of graphene devices for L < 5 μm that have been ascribed to L approaching the "quasi-ballistic limit" for graphene, 21 and with reports of "negative contact resistance" extracted by TLM for short L devices. 22 Importantly, during the UVO treatment of the contact region the graphene channel of the device remained masked by the photoresist. From the nearly unchanged values for sheet resistance we conclude that the channel properties of the devices are not greatly affected by our contact treatment method.…”

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Ultraviolet/ozone treatment to reduce metal-graphene contact resistance

Li¹,

Liang²,

Yu³

et al. 2013

Applied Physics Letters

122

105

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We report reduced contact resistance of single-layer graphene devices by using ultraviolet ozone (UVO) treatment to modify the metal/graphene contact interface. The devices were fabricated from mechanically transferred, chemical vapor deposition (CVD) grown, single layer graphene. UVO treatment of graphene in the contact regions as defined by photolithography and prior to metal deposition was found to reduce interface contamination originating from incomplete removal of poly(methyl methacrylate) (PMMA) and photoresist. Our control experiment shows that exposure times up to 10 minutes did not introduce significant disorder in the graphene as characterized by Raman spectroscopy. By using the described approach, contact resistance of less than 200 Ω μm was achieved, while not significantly altering the electrical properties of the graphene channel region of devices.

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“…It should be noted that G sq was calculated using the effective channel length, L + d, which includes carrier transport underneath the metal contacts. For simplicity, the doping level of the contacted region and the degree of charge density depinning 24 was assumed to be constant.…”

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

Nouchi

Tanigaki

2014

Applied Physics Letters

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Graphene field-effect transistors with source/drain contacts made of metals that can be easily oxidized such as ferromagnetic metals often display a double dip structure in the transfer characteristics because of charge density depinning at the contacts. Generally, transfer characteristics of field-effect transistors show no dependence on the length of the source/drain contacts because charge carrier injection occurs mainly at the edges of the contact. However, the shape of the transfer characteristics of devices fabricated using Ni contacts is found to be dependent on the length of the contact. This peculiar behavior was attributed to charge carrier injection from near the center of the contacts. This is because of oxygen diffusion and the resultant formation of an interfacial oxide layer of non-uniform thickness. The observed contact length dependent transfer characteristics were reproduced using a model calculation that includes charge carrier injection from the center of the electrode and subsequent charge transport underneath the metal contact.

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Observation of negative contact resistances in graphene field-effect transistors

Cited by 25 publications

References 23 publications

Contact resistance at planar metal contacts on bilayer graphene and effects of molecular insertion layers

Contact resistance at planar metal contacts on bilayer graphene and effects of molecular insertion layers

Ultraviolet/ozone treatment to reduce metal-graphene contact resistance

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

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