Local solid phase growth of few-layer graphene on silicon carbide from nickel silicide supersaturated with carbon

Abstract

Patterned few-layer graphene (FLG) films were grown by local solid phase epitaxy from nickel silicide supersaturated with carbon, following a fabrication scheme which allows the formation of self-aligned ohmic contacts on FLG and is compatible with conventional SiC device processing methods. The process was realised by the deposition and patterning of thin Ni films on semiinsulating 6H-SiC wafers followed by annealing and the selective removal of the resulting nickel silicide by wet chemistry. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to confirm both the formation and subsequent removal of nickel silicide. The impact of process parameters such as the thickness of the initial Ni layer, annealing temperature, and cooling rates on the FLG films was assessed by Raman spectroscopy, XPS and atomic force microscopy (AFM).The thickness of the final FLG film estimated from the Raman spectra varied from 1 to 4 monolayers for initial Ni layers between 3 and 20 nm thick. Self-aligned contacts were formed on these patterned films by contact photolithography and wet etching of nickel silicide, which enabled the fabrication of test structures to measure the carrier concentration and mobility in the FLG films.A simple model of diffusion-driven solid phase chemical reaction was used to explain formation of the FLG film at the interface between nickel silicide and silicon carbide.

Growth and Characterization of Graphene on Polycrystalline SiC Substrate Using Heating by CO2 Laser Beam

“…This D and D'-bands comes from double-resonant processes and they are related to the presence of defects and structural disorder in graphene 31,32 . Therefore, the relative integrated intensity (area) ratio of the D and G bands, A(D)/A(G), in some works presented as I D /I G , is used to evaluate the defect concentration of the graphene films 25 . From the A(D)/A(G) ratio, it is possible to determine the cristallite size, L a , by using Eq.1,…”

“…Therefore, Si atoms will be sublimated and the graphitization will be able to occur, where the C atoms on the top of surface are rearranged to synthesize the epitaxial graphene 4,[16][17][18][19] . In order to create alternative processes, some studies have shown that the addition of a layer of "catalyst material" (such as Ni or Co) promotes the reduction of the temperature required for SiC decomposition [23][24][25][26] . Nevertheless, despite SiC dissociation is promoted in this case, the Si sublimation does not occur; rather a chemical reaction to form a silicide phase between the catalyst material and Si happens.…”

Combining graphene with silicon carbide: synthesis and properties – a review

“…[149] Yoneda et al [145] and Escobedo-Cousin et al [149] reported the significant meaning of the face polarity effect for the Ni-mediated process. It was revealed that the thickness of Cface graphene (1ML [145], 1.7ML [149]) is smaller than that of Si-face graphene (2ML [145], 3.3ML [149]). Such a difference can be explained by a faster reaction rate for Ni with the Si-C bilayer than with the C-Si bilayers [145].…”

“…To elucidate the nature of the Ni-mediated graphene growth mechanism on silicon carbide, Escobedo-Cousin et al [149] experimentally studied the effect of the different growth conditions (Ni layer thickness, annealing temperature, and cooling rate) on the graphene formation. Based on the results of the XPS and Raman characterization, these authors conclude that (i) slowing the cooling rate leads to the formation of graphene layers with higher quality, (ii) higher annealing temperature promotes graphene formation with larger domain size and (iii) there is no a direct correlation between graphene thickness and Ni film thickness since the former tends to reach saturation with increasing the latter.…”

“…Several different approaches have been proposed to decrease the growth temperature, for example, Ni-induced graphene formation [142][143][144][145][146][147][148][149], segregation method using Co/SiC system [150][151][152], catalytic alloy approach [153] and Ga-mediated liquid phase growth [154,155]). …”