In-situ terahertz optical Hall effect measurements of ambient effects on free charge carrier properties of epitaxial graphene

Knight, Sean; Hofmann, Tino; Bouhafs, Chamseddine; Armakavicius, Nerijus; Kühne, Philipp; Stanishev, V.; Ivanov, Ivan Gueorguiev; Yakimova, Rositsa; Wimer, Shawn; Schubert, M.; Darakchieva, Vanya

doi:10.1038/s41598-017-05333-w

Cited by 29 publications

(20 citation statements)

References 41 publications

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“…We have recently reported similar findings for single layer graphene exposed to N 2 and He with 0% relative humidity [72]. Here, an increase of the electron density is observed, independent of the relative humidity, when N 2 is injected into the gas cell.…”

Section: In-situ Thz Ohesupporting

confidence: 67%

See 1 more Smart Citation

Advanced Terahertz Frequency-Domain Ellipsometry Instrumentation for In Situ and Ex Situ Applications

Kühne

Armakavicius

Stanishev

et al. 2018

IEEE Trans. THz Sci. Technol.

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Abstract-We present a terahertz (THz) frequency-domain spectroscopic (FDS) ellipsometer design which suppresses formation of standing waves by use of stealth technology approaches. The strategy to suppress standing waves consists of three elements geometry, coating and modulation. The instrument is based on the rotating analyzer ellipsometer principle and can incorporate various sample compartments, such as a superconducting magnet, in-situ gas cells or resonant sample cavities, for example. A backward wave oscillator and three detectors are employed, which permit operation in the spectral range of 0.1-1 THz (3.3-33 cm −1 or 0.4-4 meV). The THz frequency-domain ellipsometer allows for standard and generalized ellipsometry at variable angles of incidence in both reflection and transmission configurations. The methods used to suppress standing waves and strategies for an accurate frequency calibration are presented. Experimental results from dielectric constant determination in anisotropic materials, and free charge carrier determination in optical Hall effect, resonant-cavity enhanced optical Hall effect and in-situ optical Hall effect experiments are discussed. Examples include silicon and sapphire optical constants, free charge carrier properties of two dimensional electron gas in group-III nitride high electron mobility transistor structure, and ambient effects on free electron mobility and density in epitaxial graphene.

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Section: In-situ Thz Ohesupporting

confidence: 67%

“…Further details discussing the scattering mechanisms in epitaxial graphene under exposure of different gases can be found in Ref. [72].…”

Section: In-situ Thz Ohementioning

confidence: 99%

Advanced Terahertz Frequency-Domain Ellipsometry Instrumentation for In Situ and Ex Situ Applications

Kühne

Armakavicius

Stanishev

et al. 2018

IEEE Trans. THz Sci. Technol.

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“…The CE measurements were performed at room temperature by placing the sample on either of the two sides of a permanent magnet with field strength of B = 0.548 T and an external cavity of ∼ 100 µm [33]. In − situ environmental control gas cell was employed to measure in different gases and relative humidity (RH) parameters [31,34]. Data collected at magnetic fields B = +0.548 T and B = −0.548 T and their differences were simultaneously analyzed using a stratified optical model with parameterized model dielectric tensor (MDF) following the methodology described in Ref.…”

Section: Methodsmentioning

confidence: 99%

Critical View on Buffer Layer Formation and Monolayer Graphene Properties in High-Temperature Sublimation

Stanishev¹,

Armakavicius²,

Bouhafs³

et al. 2021

Preprint

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In this work we have critically reviewed the processes in high-temperature sublimation growth of graphene in Ar atmosphere using enclosed graphite crucible. Special focus is put on buffer layer formation and free charge carrier properties of monolayer graphene and quasi-freestanding monolayer garphene on 4H-SiC. We show that by introducing Ar at different temperatures, TAr one can shift to higher temperatures the formation of the buffer layer for both n-type and semi-insulating substrates. A scenario explaining the observed suppresed formation of buffer layer at higher TAr is proposed and discussed. Increased TAr is also shown to reduce the sp3 hybridization content and defect densities in the buffer layer on n-type conductive substrates. Growth on semi-insulating substrates results in ordered buffer layer with significantly improved structural properties, for which TAr plays only a minor role. The free charge density and mobility parameters of monolayer graphene and quasi-freestanding monolayer graphene with different TAr and different environmental treatment conditions are determined by contactless terahertz optical Hall effect. An efficient annealing of donors on and near the SiC surface takes place in intrinsic monolayer graphene grown at 2000∘C, and which is found to be independent of TAr. Higher TAr leads to higher free charge carrier mobility parameters in both intrinsically n-type and ambient p-type doped monolayer graphene. TAr is also found to have a profound effect on the free hole parameters of quasi-freestanding monolayer graphene. These findings are discussed in view of interface and buffer layer properties in order to construct a comprehensive picture of high-temperature sublimation growth and provide guidance for growth parameters optimization depending on the targeted graphene application.

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“…Important to mention that recently, the J. W. Woollam Co, the leading producer of ellipsometry equipment, has introduced the first commercial THz ellipsometer [20]. doping significantly due to adsorption of p-type dopants [23,31].…”

Section: Ellipsometry At Long Wavelengthsmentioning

confidence: 99%

Free charge carrier properties in group III nitrides and graphene studied by THz-to-MIR ellipsometry and optical Hall effect

Armakavicius

2019

Linköping Studies in Science and Technology. Dissertations

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Development of silicon based electronics have revolutionized our every day life during the last five decades. Nowadays silicon based devices operate close to their theoretical limits that is becoming a bottleneck for further progress. In particular, for the growing field of high frequency and high power electronics, silicon cannot offer the required properties. Development of materials capable of providing high current densities, carrier mobilities and high breakdown fields is crucial for further progress in state of the art electronics. Epitaxial graphene grown on semi-insulating silicon carbide substrates has a high potential to be integrated in current planar device technologies. High electron mobilities and sheet carrier densities make graphene extremely attractive for high frequency analog applications. One of the remaining challenges is the interaction of epitaxial graphene with the substrate. Typically, much lower free charge carrier mobilities, compared to free standing graphene, and doping, due to charge transfer from the substrate, is reported.

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In-situ terahertz optical Hall effect measurements of ambient effects on free charge carrier properties of epitaxial graphene

Cited by 29 publications

References 41 publications

Advanced Terahertz Frequency-Domain Ellipsometry Instrumentation for In Situ and Ex Situ Applications

Advanced Terahertz Frequency-Domain Ellipsometry Instrumentation for In Situ and Ex Situ Applications

Critical View on Buffer Layer Formation and Monolayer Graphene Properties in High-Temperature Sublimation

Free charge carrier properties in group III nitrides and graphene studied by THz-to-MIR ellipsometry and optical Hall effect

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