| AVS 63rd International Symposium & Exhibition | |
| Spectroscopic Ellipsometry Focus Topic | Friday Sessions |
| Session EL+AS+EM+MI+TF-FrM |
| Session: | Spectroscopic Ellipsometry: Novel Applications and Theoretical Approaches |
| Presenter: | Tino Hofmann, University of North Carolina at Charlotte |
| Authors: | S. Knight, University of Nebraska-Lincoln C. Bouhafs, Linköping University, Sweden N. Armakavicius, Linköping University, Sweden P. Kühne, Linköping University, Sweden V. Stanishev, Linköping University, Sweden R. Yakimova, Linköping University, Sweden S. Wimer, University of Nebraska-Lincoln M. Schubert, University of Nebraska-Lincoln V. Darakchieva, Linköping University, Sweden T. Hofmann, University of North Carolina at Charlotte |
| Correspondent: | Click to Email |
Recently, the cavity-enhanced THz optical Hall effect (THz-OHE) has been demonstrated as non-contact method to obtain free charge carrier properties using low-field permanent magnets [1,2]. A tunable, externally-coupled cavity is used to enhance the THz-OHE signal which allows the accurate determination of a sample's free charge carrier properties even at low magnetic fields. In this work we take advantage of this approach by integrating the permanent magnet into a gas flow cell. We demonstrate for the first time the application of the cavity-enhanced THz-OHE for the in-situ characterization of free charge carrier properties of monolayer graphene on Si-face 4H-SiC as a function of ambient conditions. The experiments were performed using a new rotating-analyzer THz ellipsometer at Linköping University. Upon changing the CO2, H2O, and O2 concentration in the cell, large variations in both free charge carrier sheet density NS and mobility µ are observed for the n-type graphene. The lowest NS was found for the as-grown sample with NS =5.9(1) × 1011 cm-2 where µ =2507(57) cm2/Vs. The highest NS was found after purging the sample with nitrogen for 6 hours with NS =2.43(4) × 1012 cm-2 where µ =1604(23) cm2/Vs. These significant changes are attributed to a redox-reaction of oxygen and water at the graphene surface which results in the extraction of electrons from graphene [3]. This will be discussed in detail in our presentation. We further observe that this doping mechanism is only partially reversible at room temperature upon removal of oxygen, carbon dioxide, and water by purging the cell with nitrogen. In conclusion, we demonstrate in-situ THz-OHE as a new and powerful technique to determine ambient-dependent doping mechanisms which is illustrated here using monolayer epitaxial graphene on Si-face 4H-SiC.
[1] S. Knight, S. Schöche, V. Darakchieva, P. Kühne, J.-F. Carlin, N. Grandjean, C. M. Herzinger, M. Schubert, and T. Hofmann, Opt. Lett. 40, 2688 (2015).
[2] P. Kühne, C.M. Herzinger, M. Schubert, J.A. Woollam, and T. Hofmann, Rev. Sci. Instrum. 85, 071301 (2014).
[3] A.N. Sidorov, K. Gaskill, M.B. Nardelli, J.L. Tedesco, R.L. Myers-Ward, C.R. Eddy Jr., T. Jayasekera, K.W. Kim, R. Jayasingha, A. Sherehiy, R. Stallard, and G.U. Sumanasekera, J. Appl. Phys. 111, 113706 (2012).