CNR ExploRA

Articolo in rivista, 2021, ENG, 10.1088/1361-6528/abb72b

Nanoscale structural and electrical properties of graphene grown on AlGaN by catalyst-free chemical vapor deposition

Giannazzo, F.; Dagher, R.; Schiliro, E.; Panasci, S. E.; Greco, G.; Nicotra, G.; Roccaforte, F.; Agnello, S.; Brault, J.; Cordier, Y.; Michon, A.

CNR; Univ Cote Azur; Univ Catania; Univ Palermo

The integration of graphene (Gr) with nitride semiconductors is highly interesting for applications in high-power/high-frequency electronics and optoelectronics. In this work, we demonstrated the direct growth of Gr on Al0.5Ga0.5N/sapphire templates by propane (C3H8) chemical vapor deposition at a temperature of 1350 degrees C. After optimization of the C(3)H(8)flow rate, a uniform and conformal Gr coverage was achieved, which proved beneficial to prevent degradation of AlGaN morphology. X-ray photoemission spectroscopy revealed Ga loss and partial oxidation of Al in the near-surface AlGaN region. Such chemical modification of a similar to 2 nm thick AlGaN surface region was confirmed by cross-sectional scanning transmission electron microscopy combined with electron energy loss spectroscopy, which also showed the presence of a bilayer of Gr with partial sp(2)/sp(3)hybridization. Raman spectra indicated that the deposited Gr is nanocrystalline (with domain size similar to 7 nm) and compressively strained. A Gr sheet resistance of similar to 15.8 k omega sq(-1)was evaluated by four-point-probe measurements, consistently with the nanocrystalline nature of these films. Furthermore, nanoscale resolution current mapping by conductive atomic force microscopy indicated local variations of the Gr carrier density at a mesoscopic scale, which can be ascribed to changes in the charge transfer from the substrate due to local oxidation of AlGaN or to the presence of Gr wrinkles.

Nanotechnology (Bristol. Print) 32 (1)