Atomic-Scale Characterization of Graphene p–n Junctions for Electron-Optical Applications

Zhou, Xiaodong; Kerelsky, Alexander; Elahi, Mirza M.; Wang, Dennis; Habib, K. M. Masum; Sajjad, Redwan N.; Agnihotri, Pratik; Lee, Ji Ung; Ghosh, Avik W.; Ross, Frances M.; Pasupathy, Abhay

doi:10.1021/acsnano.8b09575

Cited by 17 publications

(29 citation statements)

References 43 publications

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“…In particular it rules out the importance of junction roughness (see ref. 53 ) or frozen disorder in controlling CR’s transmission. The former should lead to appreciable deviations from Fresnel relations and the latter to a saturation of the phonon mean-free-path effect at low temperature, both of which are not observed.…”

Section: Resultsmentioning

confidence: 99%

A corner reflector of graphene Dirac fermions as a phonon-scattering sensor

et al. 2019

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Dirac fermion optics exploits the refraction of chiral fermions across optics-inspired Klein-tunneling barriers defined by high-transparency p-n junctions. We consider the corner reflector (CR) geometry introduced in optics or radars. We fabricate Dirac fermion CRs using bottom-gate-defined barriers in hBN-encapsulated graphene. By suppressing transmission upon multiple internal reflections, CRs are sensitive to minute phonon scattering rates. Here we report on doping-independent CR transmission in quantitative agreement with a simple scattering model including thermal phonon scattering. As a signature of CRs, we observe Fabry-Pérot oscillations at low temperature, consistent with single-path reflections. Finally, we demonstrate high-frequency operation which promotes CRs as fast phonon detectors. Our work establishes the relevance of Dirac fermion optics in graphene and opens a route for its implementation in topological Dirac matter.

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Section: Resultsmentioning

confidence: 99%

A corner reflector of graphene Dirac fermions as a phonon-scattering sensor

et al. 2019

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“…This is why many groups choose to use metallic bottom gates to screen charge inhomogeneities. Graphite flakes are particularly popular for this purpose, due to their compatibility with the hBN-G-hBN heterostructures [80,[125][126][127][128]. However, graphite being a microwave absorber, it cannot be used in our high frequency devices.…”

Section: Nanofabrication Of Encapsulated Graphene Devicesmentioning

confidence: 99%

“…A recent experimental work by Zhou et al [128] points out the importance of minimizing the junction roughness in order to obtain well-defined interfaces for Dirac fermion optics experiments. They study the effective junction roughness of gate-induced p-n junctions using scanning tunneling microscopy.…”

Section: Remarks On the Junction Roughnessmentioning

confidence: 99%

“…While an STM study of our tungsten/gold-gate induced p-n junctions goes beyond the scope of this thesis, I would like to point out two arguments as to why our p-n junctions should be comparable in quality to the graphite-gate-induced junctions studied in ref. [128]: Firstly, we use high-resolution electron beam lithography to define our gate electrodes, creating gaps on the order of 20 nm (see fig. 2.4d-f with increasing zoom), i.e.…”

Section: Remarks On the Junction Roughnessmentioning

confidence: 99%

“…Dirac fermion optics has also been explored beyond the pure transport approach, e.g. by combining transport with scanning gate microscopy to probe a DFO lens [206] or with scanning tunneling microscopy and spectroscopy to characterize the local doping profile of graphene p-n junctions at the atomic scale [128].…”

Section: Other Dfo Studiesmentioning

confidence: 99%

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Dirac fermion optics and plasmonics in graphene microwave devices

Graef

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This thesis addresses the physics of non-interacting and interacting Dirac fermions in ballistic graphene. Three main phenomena are investigated: Dirac fermion optics in electronic prisms defined by p-n junctions, GHz plasmonics in plasma resonance capacitors, and the breakdown of the integer quantum Hall effect (QHBD) by a magnetoexciton instability. Our technology relies on h-BN encapsulated graphene devices characterized by DC to GHz electronic transport and noise.We first study the total internal reflection of electrons in a gate-defined corner reflector. Both geometric and coherent electron optics effects are demonstrated and the device is shown to be sensitive to minute phonon scattering rates. It is then used as a proof-of-concept for GHz electron optics experiments in graphene.We introduce top-gated graphene field-effect capacitors as a platform to study ultralong wavelength plasmons characterized with a vector network analyzer. We simultaneously measure resistivity, capacitance and kinetic inductance. We observe a resonance at 40 GHz with a quality factor of two, corresponding to a plasmon of 100 µm wavelength. This result sets a milestone for the realization of resonant plasmonic devices.We finally move our attention to the QHBD in a bilayer graphene sample. DC transport and GHz noise measurements show that the elusive intrinsic breakdown field can be reached in graphene. Its signature is an abrupt increase of noise, with a super-Poissonian Fano factor. We propose a magnetoexciton instability scenario as the origin of breakdown.These results show how progress in sample fabrication has enabled us to study new classes of ballistic devices, to explore new fundamental phenomena and to envision more complex experiments like: time-of-flight measurements of acoustic phonons, characterization of plasmon propagation in bipolar superlattices, or breakdown in single layer graphene. In terms of applications, this thesis paves the way for room-temperature electron optics devices, plasma-resonance-based THz detectors, and improvement of quantum Hall resistance standards.

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Periodic Nanoarray of Graphene pn‐Junctions on Silicon Carbide Obtained by Hydrogen Intercalation

Karakachian

Rosenzweig

Nguyen

et al. 2022

Adv Funct Materials

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Graphene pn‐junctions offer a rich portfolio of intriguing physical phenomena. They stand as the potential building blocks for a broad spectrum of future technologies, ranging from electronic lenses analogous to metamaterials in optics, to high‐performance photodetectors important for a variety of optoelectronic applications. The production of graphene pn‐junctions and their precise structuring at the nanoscale remains to be a challenge. In this work, a scalable method for fabricating periodic nanoarrays of graphene pn‐junctions on a technologically viable semiconducting SiC substrate is introduced. Via H‐intercalation, 1D confined armchair graphene nanoribbons are transformed into a single 2D graphene sheet rolling over 6H‐SiC mesa structures. Due to the different surface terminations of the basal and vicinal SiC planes constituting the mesa structures, different types of charge carriers are locally induced into the graphene layer. Using angle‐resolved photoelectron spectroscopy, the electronic band structure of the two graphene regions are selectively measured, finding two symmetrically doped phases with p‐type being located on the basal planes and n‐type on the facets. The results demonstrate that through a careful structuring of the substrate, combined with H‐intercalation, integrated networks of graphene pn‐junctions could be engineered at the nanoscale, paving the way for the realization of novel optoelectronic device concepts.

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Atomic-Scale Characterization of Graphene p–n Junctions for Electron-Optical Applications

Cited by 17 publications

References 43 publications

A corner reflector of graphene Dirac fermions as a phonon-scattering sensor

A corner reflector of graphene Dirac fermions as a phonon-scattering sensor

Dirac fermion optics and plasmonics in graphene microwave devices

Periodic Nanoarray of Graphene pn‐Junctions on Silicon Carbide Obtained by Hydrogen Intercalation

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