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

Abstract

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...

Reference-free THz-TDS conductivity analysis of thin conducting films

“…Terahertz time-domain spectroscopy (THz-TDS) is maturing as a large-area, fast, accurate and non-invasive measurement technique for extracting the electrical properties of graphene [1][2][3][4][5]. Numerous studies on the applicability of THz-TDS for electrical characterization of graphene exist and conductivity mapping for graphene samples up to 25 × 30 cm 2 in size have been demonstrated [2,6].…”

Case studies of electrical characterisation of graphene by terahertz time-domain spectroscopy

“…Values of σ DC extracted from THz-TDS conductivity spectra following the Drude model have been validated several times against Hall and M4PP measurements [6,8,11,33,47]. There is however comparatively limited data available [62,71] for measurements of graphene whenσ s (ω) does not appear to follow the Drude model and in particular for measurements at 4 inch wafer-scale.…”

“…Complementary measurements have been performed in many cases in order to validate the extracted electrical properties of graphene measured by THz-TDS [14]. The measurements conducted for comparison with THz-TDS varies across a range of characterization methods including optical microscopy [29,45], Hall measurements [6,9,12,46], Raman spectroscopy [5,8,41], Kelvin probe force microscopy [8,47], and micro four-point probe (M4PP) measurements [5,8,33,48]. M4PP is a unique metrology technology developed by DTU and Capres A/S where the conductance is measured across a conducting wafer or thin film, using a 12-point microfabricated probe, with a probe pitch down to 1 µm [5,14,33,[49][50][51][52].…”

Surface restoration of polycrystalline Sb2Se3 thin films by conjugated molecules enabling high-performance photocathodes for photoelectrochemical water splitting

“…3f), respectively, which are both slightly larger than that of the bare Sb2Se3 (300 mV). The Φ values, calculated by the equation ΦSb2Se3 = ΦTip − eUSb2Se3/CPD [34], was 4.51, 4.49, and 4.46 eV for Sb2Se3, Sb2Se3/AL/4ACA, and Sb2Se3/AL/PABA, respectively. Fig.…”