5:00 PM - QN03.06.06
An Investigation of Carrier Mobility in MoS2 Grown by Chemical Vapour Deposition in a 300mm Reactor
Emma Coleman1,Paul Hurley1,Scott Monaghan1,Jun Lin1,Farzan Gity1,Michael Schmidt1,James Connolly1,Lee Walsh1,Karim Cherkaoui1,Katie O Neill2,Niall McEvoy2,Cormac O'Coileain2,Colm O'Dwyer3,Georg Duesberg4,Ian Povey1
Tyndall National Institute1,CRANN, Trinity College Dublin2,University College Cork3,Universität der Bundeswehr München4
Two dimensional (2D) van der Waals bonded materials exhibit a range of electronic properties spanning from semi-metals through to wide bandgap semiconductors. Potential applications include electronics, sensors and display technologies . In relation to practical device applications, research is focussed on large area growth [2 - 6], stable approaches to doping and contacting [7,8]. We report on the structural properties and carrier mobility in thin films (2-10nm) of MoS2 grown in a commercial 300mm atomic layer deposition reactor. The MoS2 films are grown on sapphire and SiO2/Si substrates at temperatures in the range of 350oC to 550oC by a chemical vapour deposition process using Mo(CO)6 and H2S precursors.
Analysis of the films with Raman, X-ray photoelectron spectroscopy and electron backscattered diffraction all confirm the films as MoS2. The carrier concentration, carrier type and carrier mobility are studied with Hall measurements. Excellent ohmic behaviour is achieved on MoS2 (10nm, 550oC with no post grown annealing) deposited on sapphire and a-Al2O3/sapphire substrates. Room temperature Hall analysis of the MoS2 films indicates that the non-intentionally doped MoS2 films are n-type with very low carrier concentrations of ~1014cm-3. Comparison of the free carrier concentrations in the grown films (~1014cm-3 ) to Hall analysis of natural and synthetic MoS2 crystals (1x1016 to 1x1017 cm-3) , is consistent with the presence of electrically active defect states in the energy gap of the MoS2 for the polycrystalline CVD grown films . MoS2 films grown at 350oC and subsequently annealed at 550oC in a H2S/H2 ambient indicate a significant increase in the electron concentration (~8x1016 cm-3).
The electron mobility is in the range of 3 to 17 cm2/V.s for films grown at 550oC (with comparable values for MoS2 films grown at 350oC and subsequently annealed at 550oC in a H2S/H2). Electron mobility values up to ~ 17 cm2/Vs for a MoS2 grain size in the 5nm to 20nm range in this work, compared to values in the range of 25 to 30 cm2/Vs reported by K. Kang et al.,  for monolayer MoS2 with a grain size around 1µm. This motivates the need to investigate scattering mechanisms and the influence of grain size on electron mobility in CVD grown MoS2, and preliminary results will be shown on the temperature dependence of electron concentration and electron mobility in the CVD grown MoS2 films.
 Geim,A.K.& Grigorieva,I.V. Van der Waals Heterostructures. Nature 499,419–425 (2013).
 Lin,Y.-C.etal. Wafer-scale MoS2 thin layers prepared by MoO3 sulfurization. Nanoscale 4, 6637–6641(2012).
 Kang et al., Nature, 2015, 520, 656–660
 S. M. Eichfeld, L. Hossain, Y. C. Lin, A. F. Piasecki, B. Kupp, A. G. Birdwell, R. A. Burke, N. Lu, X. Peng, J. Li, A. Azcatl, S. McDonnell, R. M. Wallace, M. J. Kim, T. S. Mayer, J. M. Redwing, and J. A. Robinson, ACS Nano, 9, 2080 (2015).
 . M. O’Brien, N. McEvoy, N. Hallam, H. Kim, N. C. Berner, D. Hanlon, K. Lee, J. N. Coleman, and G. S. Duesberg, Sci. Rep., 4, 7374 (2014).
 L. A. Walsh, R. Addou, R. M. Wallace, and C. L. Hinkle, in Molecular Beam Epitaxy: From Research to Mass Production, Second ed., M. Henini, Editor, p. 515, Elsevier, New York (2018).
 C. Zhou, Y. Zhao, S. Raju, Y. Wang, Z. Lin, M. Chan, Y. Chai, Adv. Funct. Mater. 2016, 26, 4223
 Gioele Mirabelli, Michael Schmidt, Brendan Sheehan, Karim Cherkaoui, Scott Monaghan, Ian Povey, Melissa McCarthy, Alan P Bell, Roger Nagle, Felice Crupi, Paul K Hurley, Ray Duffy, “Back-gated Nb-doped MoS2 junctionless field-effect-transistors” AIP Advances, 6, 2 , 025323 (2016)
 Monaghan, S. Gity, F., Duffy, R., Mirabelli, G., McCarthy, M., Cherkaoui, K., Povey, I.M., Nagle, R.E., Hurley, P.K., Lindemuth, J.R., Napolitani, E. “Hall-effect mobility for a selection of natural and synthetic 2D semiconductor crystals” Proceedings of ULIS 2017, 27, 7962592 (2017)
 Arend M. van der Zande et al., Nature Materials, 12, 554 (2013)