Electrical Homogeneity Mapping of Epitaxial Graphene on Silicon Carbide

Whelan, Patrick Rebsdorf; Panchal, Vishal; Petersen, Dirch Hjorth; Mackenzie, David; Melios, Christos; Pasternak, Iwona; Gallop, John; Østerberg, Frederik Westergaard; Jepsen, Peter Uhd; Strupiński, Włodek; Kazakova, Olga; Bøggild, Peter

doi:10.1021/acsami.8b11428

Cited by 21 publications

(32 citation statements)

References 46 publications

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“…The features observed in these maps have been reported in the literature in 16,48 , and they can be related to the presence of microscopic defects, such as cracks, and to the presence of growth domain. The measurements are affected by edge effects that span about 1 mm from the edge due to the size of the THz beam, which is estimated to be 0.5 mm in diameter.…”

Section: Evsupporting

confidence: 64%

Towards standardisation of contact and contactless electrical measurements of CVD graphene at the macro-, micro- and nano-scale

Melios

Huáng

Callegaro

et al. 2020

Sci Rep

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Graphene has become the focus of extensive research efforts and it can now be produced in waferscale. for the development of next generation graphene-based electronic components, electrical characterization of graphene is imperative and requires the measurement of work function, sheet resistance, carrier concentration and mobility in both macro-, micro-and nano-scale. Moreover, commercial applications of graphene require fast and large-area mapping of electrical properties, rather than obtaining a single point value, which should be ideally achieved by a contactless measurement technique. We demonstrate a comprehensive methodology for measurements of the electrical properties of graphene that ranges from nano-to macro-scales, while balancing the acquisition time and maintaining the robust quality control and reproducibility between contact and contactless methods. the electrical characterisation is achieved by using a combination of techniques, including magneto-transport in the van der pauw geometry, tHz time-domain spectroscopy mapping and calibrated Kelvin probe force microscopy. The results exhibit excellent agreement between the different techniques. Moreover, we highlight the need for standardized electrical measurements in highly controlled environmental conditions and the application of appropriate weighting functions.The unique properties of graphene 1 and the increasing demand for large-scale production were the reason for the development of various industrial methods to grow this material. One of the most promising methods is the use of CVD to grow graphene onto various metallic substrates. In CVD growth, graphene is grown on the surface of the metal after hydrocarbons decompose 2 . The most promising metal substrate used until now is Cu 3 , however graphene is currently grown also on Ni(111) 4-6 , Ru(0001) 7 , Pt(111) 8,9 , and Ir(111) 9-11 . Subsequently to the growth process, for graphene to be use in electronic applications, it needs to be transferred on an insulating substrate (i.e. Si/SiO 2 , quartz or polyethylene terephthalate (PET), which is a transparent and flexible substrate). The already happening now use of graphene in RF electronics 12 , integrated circuits 13 and optoelectronics 14 has triggered impressive progress in large-scale production, however the community still lacks standardised electrical measurements to extract useful parameters such as carrier concentration, mobility and sheet resistance, all of those are often presented as figures-of-merit of the graphene quality. Currently, the most widely used method for electrical characterisation involves magneto-transport measurements in lithographically patterned Hall bars to extract carrier concentration, mobility and resistance. However, this method is not suitable for high throughput characterisation and often the measured graphene is significantly altered due to the microfabrication processes, in which case the electrical properties of the pristine transferred graphene are different from the ones measured. An alternative method fo...

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Section: Evsupporting

confidence: 64%

Towards standardisation of contact and contactless electrical measurements of CVD graphene at the macro-, micro- and nano-scale

Melios

Huáng

Callegaro

et al. 2020

Sci Rep

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“…We remark that Fermi velocity renormalization effects described here only influence the extracted values of n and µ from THz-TDS measurements (see section 2). As such, previously measured and reported values of σ DC and τ in the literature [15,16,[21][22][23]36,42] are accurate, i.e. not affected by this correction.…”

Section: Discussionmentioning

confidence: 68%

Fermi velocity renormalization in graphene probed by terahertz time-domain spectroscopy

Whelan¹,

Shen²,

Zhou³

et al. 2020

2D Mater.

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We demonstrate terahertz time-domain spectroscopy (THz-TDS) to be an accurate, rapid and scalable method to probe the interaction-induced Fermi velocity renormalization ν F * of charge carriers in graphene. This allows the quantitative extraction of all electrical parameters (DC conductivity σ DC , carrier density n, and carrier mobility µ) of large-scale graphene films placed on arbitrary substrates via THz-TDS. Particularly relevant are substrates with low relative permittivity (< 5) such as polymeric films, where notable renormalization effects are observed even at relatively large carrier densities (> 10 12 cm -2 , Fermi level > 0.1 eV). From an application point of view, the ability to rapidly and non-destructively quantify and map the electrical (σ DC , n, µ) and electronic (ν F * ) properties of large-scale graphene on genericsubstrates is key to utilize this material in applications such as metrology, flexible electronics as well as to monitor graphene transfers using polymers as handling layers.

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“…Examples of sheet conductivity spectra from as‐grown graphene on sapphire are shown in Figure S10d in the Supporting Information. The sheet conductivity spectra did not follow the classical Drude‐model as previously observed as a reduction was noticed in the sheet conductivity at low frequencies—this indicated that the carriers in graphene did not scatter isotropically but experienced some degree of carrier localization . In such cases, the sheet conductivity was better described by the first term of the phenomenological Drude–Smith model

σ_{normals} (ω) = \frac{W_{normalD}}{(1 - i ω τ)} (1 + \frac{c}{(1 - i ω τ)})

where W D is the Drude weight related to the DC sheet conductivity as σ DC = W D (1 + c ), and c is a parameter that can take values from −1 to 0 and describes the degree of carrier localization/backscattering .…”

Section: Methodsmentioning

confidence: 82%

“…The waveforms contained transients from internal reflections within the sapphire substrate. Here, the data from the directly transmitted transients were used to extract the sheet conductivity (σ s (ω) = σ 1 + iσ 2 ) of graphene as

σ_{normals} (ω) = (\frac{n_{normalsap} + 1}{Z_{0}}) \times (\frac{1}{T_{normalfilm} (ω)} - 1)

where Z 0 is the vacuum impedance, T meas is the ratio of the Fourier transforms of the THz waveforms transmitted through graphene‐covered sapphire and bare sapphire (Figure S10b, Supporting Information), and n sap is the refractive index of sapphire (Figure S10c, Supporting Information) calculated from THz waveforms from bare sapphire relative to air …”

Section: Methodsmentioning

confidence: 99%

Wafer‐Scale Synthesis of Graphene on Sapphire: Toward Fab‐Compatible Graphene

Mishra

Forti

Fabbri

et al. 2019

Small

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117

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wafer-scale, with good crystallinity and with contamination levels compatible with large-scale back-end-of-line (BEOL) integration. At present, chemical vapor deposition (CVD) on catalytic copper (Cu) substrates is widely recognized as the most promising route to obtain scalable monolayer graphene for electronic and optoelectronic applications. [1][2][3][4] However, significant hurdles are limiting the actual integration of CVD graphene grown on Cu for most applications. In the first instance, the unavoidable transfer process over wafer-scale is rather cumbersome and introduces contamination, unintentional doping, and mechanical stress, [5][6][7] which adversely impact the physical integrity and electrical performance [8] of the graphene layer. The significant challenge involved in carrying out this seemingly straightforward task is reflected by the vast literature on large-scale transfer processes. Second, metallic contamination levels in transferred CVD graphene grown on Cu are typically well-above the specifications requested for BEOL integration. [6] Clearly, asThe adoption of graphene in electronics, optoelectronics, and photonics is hindered by the difficulty in obtaining high-quality material on technologically relevant substrates, over wafer-scale sizes, and with metal contamination levels compatible with industrial requirements. To date, the direct growth of graphene on insulating substrates has proved to be challenging, usually requiring metal-catalysts or yielding defective graphene. In this work, a metal-free approach implemented in commercially available reactors to obtain high-quality monolayer graphene on c-plane sapphire substrates via chemical vapor deposition is demonstrated. Low energy electron diffraction, low energy electron microscopy, and scanning tunneling microscopy measurements identify the Al-rich reconstruction9° of sapphire to be crucial for obtaining epitaxial graphene. Raman spectroscopy and electrical transport measurements reveal high-quality graphene with mobilities consistently above 2000 cm 2 V −1 s −1 . The process is scaled up to 4 and 6 in. wafers sizes and metal contamination levels are retrieved to be within the limits for back-end-ofline integration. The growth process introduced here establishes a method for the synthesis of wafer-scale graphene films on a technologically viable basis.

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Electrical Homogeneity Mapping of Epitaxial Graphene on Silicon Carbide

Cited by 21 publications

References 46 publications

Towards standardisation of contact and contactless electrical measurements of CVD graphene at the macro-, micro- and nano-scale

Towards standardisation of contact and contactless electrical measurements of CVD graphene at the macro-, micro- and nano-scale

Fermi velocity renormalization in graphene probed by terahertz time-domain spectroscopy

Wafer‐Scale Synthesis of Graphene on Sapphire: Toward Fab‐Compatible Graphene

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