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.
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