Out-of-plane corrugations in graphene based van der Waals heterostructures

Zihlmann, Simon; Makk, Péter; Rehmann, Mirko K.; Wang, Lujun; Kedves, Máté; Indolese, David I.; Watanabe, Kenji; Taniguchi, Takashi; Zumbühl, Dominik M.; Schönenberger, Christian

doi:10.1103/physrevb.102.195404

Cited by 11 publications

(12 citation statements)

References 33 publications

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“…It has been attributed to an enhanced dephasing rate due to a random vector potential generated by the in-plane magnetic field penetrating out-of-plane corrugations in the graphene layer. Similar effects have been observed in encapsulated devices [43,44], strongly suggesting that out-of-plane corrugations are also present in encapsulated graphene. We therefore attribute the mobility increase in our experiment to the reducing of outof-plane strain fluctuations, as illustrated in Fig.…”

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Mobility Enhancement in Graphene by in situ Reduction of Random Strain Fluctuations

et al. 2020

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Microscopic corrugations are ubiquitous in graphene even when placed on atomically flat substrates. These result in random local strain fluctuations limiting the carrier mobility of high quality hBN-supported graphene devices. We present transport measurements in hBN-encapsulated devices where such strain fluctuations can be in situ reduced by increasing the average uniaxial strain. When ∼ 0.2% of uniaxial strain is applied to the graphene, an enhancement of the carrier mobility by ∼ 35% is observed while the residual doping reduces by ∼ 39%. We demonstrate a strong correlation between the mobility and the residual doping, from which we conclude that random local strain fluctuations are the dominant source of disorder limiting the mobility in these devices. Our findings are also supported by Raman spectroscopy measurements. arXiv:1909.13484v1 [cond-mat.mes-hall]

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confidence: 72%

Mobility Enhancement in Graphene by in situ Reduction of Random Strain Fluctuations

et al. 2020

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“…To maximize the performance of a vdW material-based device, good Ohmic contact between the metal electrode and semiconductor is fundamental. , The conventional method of improving the Ohmic contact for bulk or thin-film semiconductors involves ion implantation doping in the contact regions, which is challenging in ultrathin 2D materials. , Recently, edge contact, chemical doping, and charge transfer doping have been investigated to facilitate Ohmic contact formation between metals and 2D materials. ,,− Among them, the charge-transfer doping method is a simple, industry-compatible, and low-temperature process. Postannealing, which is the conventional method for contact improvement, is undesirable to 2D materials because their physical and electrical properties can be degraded. , …”

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Recessed-Channel WSe₂ Field-Effect Transistor via Self-Terminated Doping and Layer-by-Layer Etching

et al. 2022

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Effective channel control with low contact resistance can be accomplished through selective ion implantation in Si and III–V semiconductor technologies; however, this approach cannot be adopted for ultrathin van der Waals materials. Herein, we demonstrate a self-aligned fabrication process based on self-terminated p-doping and layer-by-layer chemical etching to achieve low contact resistance as well as a high on/off current ratio in ultrathin tungsten diselenide (WSe2) field-effect transistors (FETs). Damage-free layer-by-layer thinning of the WSe2 channel is repeated up to a thickness of approximately 1.4 nm, while maintaining the selectively p-doped source/drain regions. The device characteristics of the recessed-channel WSe2 FET are systematically monitored during this layer-by-layer recess-channel process. The WSe2 etching rate is estimated to be 2–3 layers per cycle of oxidation and subsequent chemical etching. The self-terminated tungsten oxide (WOX) layer grown through ultraviolet–ozone treatment induces robust p-doping in the neighboring (or underlying) WSe2 through the electron withdrawal mechanism, which remains in the source/drain regions after channel oxide removal. The adopted self-terminated and self-aligned recess-channel process for ultrathin WSe2 FETs enables the realization of a high on/off output current ratio (>108) and field-effect mobility (∼190 cm2/V·s), while maintaining low contact resistance (0.9–6.1 kΩ·μm) without a postannealing process. The proposed facile and reproducible doping and atomic-layer-etching method for the fabrication of a recessed-channel FET with an ultrathin body can be helpful for high-performance two-dimensional semiconductor devices and is applicable to post-Si complementary metal-oxide semiconductor devices.

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“…A plausible explanation for this phenomenon is that the full solution varies more slowly in the y-direction compared to the analytical approximation in Eq. (24). The analytical solution has ∂f /∂y ∝ B, but it neglects the boundary condition that demands ∂f /∂y = 0 when y = ±W/2.…”

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“…Hence, the in-plane magnetic field will have a component orthogonal to the graphene surface, giving rise to an orbital effect. This orthogonal component has been observed to suppress phasecoherent weak localization [23,24]. Consequently, extra care must be taken when considering phase-coherent transport experiments relying on in-plane magnetic fields.…”

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Combined Zeeman and orbital effect on the Josephson effect in rippled graphene

et al. 2020

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The two-dimensional nature of graphene Josephson junctions offers the possibility of creating effective superconductor-ferromagnet-superconductor junctions with tunable Zeeman splitting caused by an in-plane magnetic field. Such junctions would be able to alternate between a conventional superconducting ground state and a ground state with an intrinsic phase difference, making them controllable 0-π Josephson junctions. However, in addition to the Zeeman splitting, an in-plane magnetic field will in general also produce an orbital effect because of height variations in graphene, colloquially known as ripples. Both the Zeeman and orbital effect will thus affect the critical current, so to be able to identify 0-π transitions it is necessary to understand their combined effect. From both analytical and numerical solutions of the Usadel equation we find that ripples can in fact produce a current response similar to that which is characteristic of a 0-π transition. Hence, additional analysis is required in order to reveal the presence of a 0-π transition caused by spin splitting in graphene with ripples. We provide a closed form analytical expression for the critical current in the presence of exchange field and ripple effects as well as an expression for the scaling of critical current zeros with junction parameters.

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Out-of-plane corrugations in graphene based van der Waals heterostructures

Cited by 11 publications

References 33 publications

Mobility Enhancement in Graphene by in situ Reduction of Random Strain Fluctuations

Mobility Enhancement in Graphene by in situ Reduction of Random Strain Fluctuations

Recessed-Channel WSe₂ Field-Effect Transistor via Self-Terminated Doping and Layer-by-Layer Etching

Combined Zeeman and orbital effect on the Josephson effect in rippled graphene

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Out-of-plane corrugations in graphene based van der Waals heterostructures

Cited by 11 publications

References 33 publications

Mobility Enhancement in Graphene by in situ Reduction of Random Strain Fluctuations

Mobility Enhancement in Graphene by in situ Reduction of Random Strain Fluctuations

Recessed-Channel WSe2 Field-Effect Transistor via Self-Terminated Doping and Layer-by-Layer Etching

Combined Zeeman and orbital effect on the Josephson effect in rippled graphene

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Product

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Recessed-Channel WSe₂ Field-Effect Transistor via Self-Terminated Doping and Layer-by-Layer Etching