Epitaxial Graphene on 4H-SiC(0001) Grown under Nitrogen Flux: Evidence of Low Nitrogen Doping and High Charge Transfer

Vélez-Fort, E.; Mathieu, Claire; Pallecchi, Emiliano; Pigneur, Marine; Silly, Mathieu G.; Belkhou, Rachid; Marangolo, M.; Shukla, Abhay; Sirotti, Fausto; Ouerghi, Abdelkarim

doi:10.1021/nn304315z

Cited by 104 publications

(107 citation statements)

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“…Only two components are present on the spectra [11] due to the bilayer graphene (G peak at binding energy BE ¼ 284.3 eV) and the SiC substrate (BE ¼ 282.6 eV). Respect to an as grown n-doped monolayer epitaxial graphene [18] the G peak presents a shift of about 0.4 eV to lower BE indicating a change in the doping, from n to p, induced by the hydrogenation process [11]. Moreover, the SiC component is shifted of about 1 eV to lower BE, which confirms that the hydrogen bonds are present at the SiC surface inducing this band bending variation [10] confirming a complete decoupling of the buffer layer.…”

Section: Resultsmentioning

confidence: 75%

Bandgap inhomogeneity of MoS2 monolayer on epitaxial graphene bilayer in van der Waals p-n junction

Aziza

Henck

Felice

et al. 2016

Carbon

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a b s t r a c tAtomically thin MoS 2 /graphene vertical heterostructures are promising candidates for nanoelectronic and optoelectronic technologies. In this work, we studied the optical and electronic properties of n doped single layer MoS 2 on p doped bilayer graphene vdW heterostructures. We demonstrate a non-uniform strain between two different orientation angles of MoS 2 monolayer on top of epitaxial bilayer graphene. A significant downshift of the E 1 2g mode, a slight downshift of the A 1g mode, and photoluminescence shift and quenching are observed between two MoS 2 monolayers differently oriented with respect to graphene; This could be mostly attributed to the strain-induced transition from direct to indirect bandgap in monolayer MoS 2 . Moreover, our theoretical calculations about differently-strained MoS 2 monolayers are in a perfect accordance with the experimentally observed behavior of differently-oriented MoS 2 flakes on epitaxial bilayer graphene. Hence, our results show that straininduced bandgap engineering of single layered MoS 2 is dependent on the orientation angle between stacked layers. These findings could be an interesting novel way to take advantage of the possibilities of MoS 2 and deeply exploit the capabilities of MoS 2 /graphene van der Waals heterostructures.© 2016 Elsevier Ltd. All rights reserved.Ever since the technique to isolate stable single-layer graphene was reported, the study of two-dimensional (2D) materials has gained a lot of research interest. Hence, a broad family of 2D materials like graphene, transition metal dichalcogenides (TMDCs), and topological insulators have been explored so far [1]. For the sake of exploring their fundamental interfacial interactions and conceiving novel electronic functionalities, vertical heterostructures composed of 2D materials stacked together by van der Waals (vdW) forces have attracted a great attention lately [2]. Among these combined structures, the MoS 2 /graphene heterostructure, among other heterostructures combining graphene with different layered 2D materials [3], shows a promising potential for next generation nanoelectronic and optoelectronic devices thanks to the outstanding carrier mobilities on one hand and the excellent optical responsivities on the other hand [4e6].However, research work about the structural quality, the band alignment and the optical emission properties of MoS 2 /graphene or graphene/MoS 2 vdW heterostructures are still limited. The exploration of such characteristic properties are fundamental to make possible the assembling of MoS 2 with graphene, pave the way for the realization of a well-ordered MoS 2 /graphene structure, and enable opportunities for a wide spectrum of optoelectronic functionalities. Inspirations of this present work arise from the fact that some of the theoretical calculations have predicted the crossover between a direct and indirect bandgap of MoS 2 originating from the modification of interlayer orientation [7e9]. Since the properties of MoS 2 /graphene heterostructure depend st...

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Section: Resultsmentioning

confidence: 75%

Bandgap inhomogeneity of MoS2 monolayer on epitaxial graphene bilayer in van der Waals p-n junction

Aziza

Henck

Felice

et al. 2016

Carbon

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“…The p-type graphene is obtained by hydrogenation of epitaxial graphene resulting from the high temperature baking of a SiC substrate 27,28 . The latter presents several advantages, in particular the lack of a transfer step between the growth and the device design.…”

Section: Resultsmentioning

confidence: 99%

Electrolytic phototransistor based on graphene-MoS2 van der Waals p-n heterojunction with tunable photoresponse

Henck

Pierucci

Chaste

et al. 2016

Applied Physics Letters

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Van der Waals (vdW) heterostructures obtained by stacking 2D materials offer a promising route for next generation devices by combining different unique properties in completely new artificial materials. In particular, the vdW heterostructures combine high mobility and optical properties that can be exploited for optoelectronic devices. Since the p-n junction is one of the most fundamental units of optoelectronics, we propose an approach for its fabrication based on the intrinsic n doped MoS2 and the p doped bilayer graphene hybrid interfaces. We demonstrate the control of the photoconduction properties using electrolytic gating which ensures a low bias operation. We show that by finely choosing the doping value of each layer, the photoconductive properties of the hybrid system can be engineered to achieve magnitude and sign control of the photocurrent. Finally, we provide a simple phase diagram relating the photoconductive behavior with the chosen doping, which we believe can be very useful for the future design of the van der Waals based photodetectors.

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“…While doping graphene by adsorbates or more elaborate chemical means has made rapid progress, [1][2][3][4][5][6][7] opening a band-gap in graphene has been problematic. Two routes to wide-band-gap semiconducting graphene have been pioneered: electron confinement and chemical functionalization.…”

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Wide-Gap Semiconducting Graphene from Nitrogen-Seeded SiC

et al. 2013

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All carbon electronics based on graphene has been an elusive goal. For more than a decade, the inability to produce significant band-gaps in this material has prevented the development of graphene electronics. We demonstrate a new approach to produce semiconducting graphene that uses a submonolayer concentration of nitrogen on SiC sufficient to pin epitaxial graphene to the SiC interface as it grows. The resulting buckled graphene opens a band-gap greater than 0.7eV in the otherwise continuous metallic graphene sheet. The goal of developing all-carbon electronics requires the ability to dope graphene and convert it between metallic and wide band-gap semiconducting forms. While doping graphene by adsorbates or more elaborate chemical means has made rapid progress, 1-7 opening a band-gap in graphene has been problematic. Two routes to wide-band-gap semiconducting graphene have been pioneered: electron confinement and chemical functionalization. Electron confinement in lithographically patterned narrow graphene ribbons has been plagued by lithographic limits and edge disorder, 8-11 although recent results from sidewall grown graphene ribbon are showing new progress that could lead to band-gaps larger than 0.6eV. 12,13 Functionalized graphene band-gaps can be produced by imposing a periodic potential in the graphene lattice through ordered adsorbates 14,15 or ordered impurities replacing carbon atoms. 16 In this work we demonstrate a novel approach to bandgap engineering in graphene using a nitrogen seeded SiC surface. Rather than using chemical vapor deposition (CVD) or plasma techniques to dope graphene by post seeding the films with nitrogen, 5-7,17 we show that a submonolayer concentration of nitrogen adsorbed on SiC, prior to graphene growth, causes a large band-gap to open in the subsequently grown, continuous graphene sheets. Using X-ray photoemission spectroscopy (XPS), scanning tunneling microscopy (STM), and angle resolved photoemission spectroscopy (ARPES), we show that a submonolayer concentration of bonded nitrogen at the graphene-SiC interface leads to a 0.7eV semiconducting form of graphene.The band-gap is not due to chemical functionalization since the concentrations used in these studies are expected to have little effect on graphene's band structure. 16,18 Instead, STM topographs and dI/dV images, showing that the graphene is buckled into folds with 1-2nm radii of curvature, suggests two possible origins for the gap: either a quasi-periodic strain 19 or electron localization in the 1-2 nm wide buckled ribbons. 20

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Epitaxial Graphene on 4H-SiC(0001) Grown under Nitrogen Flux: Evidence of Low Nitrogen Doping and High Charge Transfer

Cited by 104 publications

References 41 publications

Bandgap inhomogeneity of MoS2 monolayer on epitaxial graphene bilayer in van der Waals p-n junction

Bandgap inhomogeneity of MoS2 monolayer on epitaxial graphene bilayer in van der Waals p-n junction

Electrolytic phototransistor based on graphene-MoS2 van der Waals p-n heterojunction with tunable photoresponse

Wide-Gap Semiconducting Graphene from Nitrogen-Seeded SiC

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