Nanoscience and Nanometrology
Volume 1, Issue 1, December 2015, Pages: 1-7
Received: Jul. 5, 2015;
Accepted: Jul. 28, 2015;
Published: Jul. 29, 2015
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Gabriele Fisichella, Consiglio Nazionale delle Ricerche, Istituto per la Microelettronica e Microsistemi, Catania, Italy
Giuseppe Greco, Consiglio Nazionale delle Ricerche, Istituto per la Microelettronica e Microsistemi, Catania, Italy
Patrick Fiorenza, Consiglio Nazionale delle Ricerche, Istituto per la Microelettronica e Microsistemi, Catania, Italy
Salvatore Di Franco, Consiglio Nazionale delle Ricerche, Istituto per la Microelettronica e Microsistemi, Catania, Italy
Fabrizio Roccaforte, Consiglio Nazionale delle Ricerche, Istituto per la Microelettronica e Microsistemi, Catania, Italy
Filippo Giannazzo, Consiglio Nazionale delle Ricerche, Istituto per la Microelettronica e Microsistemi, Catania, Italy
We have exploited conductive atomic force microscopy (CAFM) to characterize the vertical current transport from graphene (Gr) to the 2D electron gas of AlxGa1 xN/GaN heterostructures considering different kinds of AlGaN surfaces in terms of roughness and unevenness. The vertical current transport mechanism can radically change depending on these nanometer size superficial fluctuations whereby the nanoscale lateral resolution of CAFM current voltage (I V) measurements offers the ideal conditions to distinguish this effect form the average macroscopic behavior. We have characterized bare and Gr coated high quality AlGaN surface at first, observing for both a rectifying behavior. In particular the contact on Gr shows a lower Schottky barrier height (SBH) (ΦB = 0.4 eV) than the bare AlGaN (ΦB = 0.9 eV), and a smaller spread between the array of sampled positions. In particular this lateral homogeneity can be explained as an averaging effect of Gr on the AlGaN surface potential fluctuations over a length scale around the AFM tip in the order of the electron mean free path of a transferred CVD grown Gr (~100 nm). In order to exclude the role of the AFM metal tip force contact to the observed behavior we have performed a force dependent characterization establishing a tip force range in which this effect is negligible. We have also repeated the same characterizations on a Gr/AlGaN/GaN heterostructure with a high structured AlGaN surface. In this case a lower SBH (ΦB = 0.6 eV) and an ohmic behavior have been observed on bare AlGaN and Gr coated AlGaN respectively. This result has been attributed to the presence of preferential current paths in correspondence of the surface voids and the contemporary collection of the AFM morphology and the current map of the bare AlGaN has confirmed it. In particular, the ohmic behavior through Gr has been imputed to a contemporary lowering of the SBH and a homogenization effect of a certain density of preferential current paths
Salvatore Di Franco,
Current mapping in Graphene Contacts to AlGaN/GaN Heterostructures, Nanoscience and Nanometrology.
Vol. 1, No. 1,
2015, pp. 1-7.
A. K. Geim and K. S. Novoselov, “The rise of graphene”, Nat. Mater., vol. 6, pp. 183-191, March. 2007.
K. I. Bolotin, K. J. Sikes, Z. Jiang, M. Klima, G. Fudenberg, J. Hone, P. Kim and H. L. Stormer, “Ultrahigh electron mobility in suspended graphene”, Solid State Commun., vol. 146, pp. 351–355, June 2008.
F. Bonaccorso, Z. Sun, T. Hasan and A. C. Ferrari, “Gra-phene photonics and optoelectronics”, Nat. Photonics, vol. 4, pp. 611– 622, Semptember 2010.
A. Balandin, S. Ghosh, W. Bao, I. Calizo, D. Teweldebrahn, F. Miao and C. N. Lau, “Superior Thermal Conductivity of Single-Layer Graphene”, Nano Lett, vol. 8, pp. 902-907, March 2008.
C. Lee, X. Wei, J. W. Kysar and J. Hone, “Measurement of the Elastic Properties and Intrinsic Strength of Monolayer Graphene”, Science, vol. 321, pp. 385-388, July 2008.
S. M. Song, J. K. Park, O. J. Sul, and B. J. Cho, “Determi-nation of work function of graphene under a metal electrode and its role in contact resistance.,” Nano Lett., vol. 12, no. 8, pp. 3887–92, Aug. 2012.
F. Xia, V. Perebeinos, Y. Lin, Y. Wu, and P. Avouris, “The origins and limits of metal-graphene junction resistance”, Nat. Nanotechnol., vol. 6, pp. 179-184. February, 2011.
H. Yang, J. Heo, S. Park, H. J. Song, D. H. Seo, K.-E. Byun, P. Kim, I. Yoo, H.-J. Chung and K. Kim, “Graphene Barristor, a Triode Device with a Gate-Controlled Schottky Barrier”, Scence, vol. 336, pp. 1140–1142, May 2012.
T. Filleter, K. V. Emtsev, T. Seyller, R. Bennewitz, “Local work function measurements of epitaxial graphene”, Appl. Phys. Lett. vol. 93, no. 133117(3), September 2008.
F. Giannazzo, S. Sonde, V. Raineri, and E. Rimini, “Screening Length and Quantum Capacitance in Graphene by Scanning Probe Microscopy”, Nano Lett. vol. 9, 23-29, De-cember 2009.
F. Giannazzo, I. Deretzis, A. La Magna, F. Roccaforte, R. Yakimova, “Electronic transport at monolayer-bilayer junc-tions in epitaxial graphene on SiC”, Phys. Rev. B vol. 86, no. 235422(6), December 2012.
F. Giannazzo, S. Sonde, R. Lo Nigro, E. Rimini, V. Raineri, “Mapping the Density of Scattering Centers Limiting the Electron Mean Free Path in Graphene”, Nano Lett., vol. 11, pp. 4612–4618, October 2011.
F. Giannazzo, V. Raineri, R. Yakimova, J.-R. Huntzinger, A. Tiberj, and J. Camassel, “Electrical properties of the gra-phene/4H-SiC (0001) interface probed by scanning current spectroscopy”, Phys. Rev. B, vol. 80, no. 241406(R), 2009.
G. Fisichella, G. Greco, F. Roccaforte, F. Giannazzo, “Current transport in graphene/AlGaN/GaN vertical het-erostructures probed at nanoscale”, Nanoscale, vol. 6, pp. 8671-8680, August 2014.
G. Fisichella, G. Greco, F. Roccaforte, and F. Giannazzo, “From Schottky to Ohmic graphene contacts to AlGaN/GaN heterostructures: Role of the AlGaN layer microstructure,” Appl. Phys. Lett., vol. 105, no. 6, no. 063117(5), August 2014.
Y. Wang, Y. Zheng, X. Xu, E. Dubuisson, Q. Bao, J. Lu, K. P. Loh, “Electrochemical Delamination of CVD-Grown Gra-phene Film: Toward the Recyclable Use of Copper Catalyst”, ACS Nano vol. 5(12), pp. 9927-9933, October 2011.
G. Fisichella, S. Di Franco, F. Roccaforte, S. Ravesi, F. Giannazzo, “Microscopic mechanisms of graphene electrolytic delamination from metal substrates”, Appl. Phys. Lett., vol. 104, no. 233105(5), June 2014.
W. Zhu, T. Low, V. Perebeinos, A. A. Bol, Y. Zhu, H. Yan, J. Tersoff and P. Avouris, “Structure and Electronic Transport in Graphene Wrinkles”, Nano Lett.vol. 12, pp. 3431-3436, May 2012.
G. Greco, F. Giannazzo, F. Iucolano, R. Lo Nigro, and F. Roccaforte, “Nanoscale structural and electrical evolution of Ta- and Ti-based contacts on AlGaN/GaN heterostructures”, J. Appl. Phys. vol. 114, no. 083717(5), August 2013.
L. Wang, F. M. Mohammed, and I. Adesida, "Differences in the reaction kinetics and contact formation mechanisms of annealed Ti/Al/Mo/Au Ohmic contacts on n-GaN and AlGaN/GaN epilayers", J. Appl. Phys. vol. 101, no. 013702(11), January 2007.
F. Iucolano, F. Roccaforte, F. Giannazzo and V. Raineri, "Barrier inhomogeneity and electrical properties of Pt/GaN Schottky contacts", J. Appl. Phys. vol. 102, no. 113701(8), December 2007.
W. Schottky, "Theory of blocking layer and point rectifiers", Z. Phys., vol. 113, pp. 367–414, 1939.
N. F. Mott, "Note on the Contact between a Metal and an Insulator or Semiconductor", Proc. Cambridge Philos. Soc., vol. 34, pp. 568, 1938.
J. P. Ibbetson, P. T. Fini, K. D. Ness, S. P. DenBaars, J. S. Speck, U. K. Mishra, "Polarization effects, surface states, and the source of electrons in AlGaN/GaN heterostructure field effect transistors", Appl. Phys. Lett. vol. 77, pp. 250-252, March 2000.