Wafer-scale graphene on SiC with uniform structural and electrical features is needed to realize graphene-based radio frequency devices and integrated circuits.Here,a continuous bi/trilayer of graphene with uniform structural and electrical features was grown on 2 inch 6H-SiC (0001) by etching before and after graphene growth.Optical and atomic force microscopy images indicate the surface morphology of graphene is uniform over the 2 inch wafer.Raman and transmittance spectra confirmed that its layer number was also uniform.Contactless resistance measurements indicated the average graphene sheet resistance was 720 /with a non-uniformity of 7.2%.Large area contactless mobility measurements gave a carrier mobility of about 450 cm2 /(V s) with an electron concentration of about 1.5×10 13 cm2.To our knowledge,such homogeneous morphology and resistance on wafer scale are among the best results reported for wafer-scale graphene on SiC.
JIA YuPing GUO LiWei LIN JingJing CHEN LianLian CHEN XiaoLong
The field emission （FE） properties of vertically aligned graphene sheets （VAGSs） grown on different SiC substrates are reported. The VAGSs grown on nonpolar SiC （10-10） substrate show an ordered alignment with the graphene basal plane-parallel to each other, and show better FE features, with a lower turn-on field and a larger field enhancement factor. The VAGSs grown on polar SiC （000-1 ） substrate reveal a random petaloid-shaped arrangement and stable current emission over 8 hours with a maximum emission current fluctuation of only 4%. The reasons behind the differing FE characteristics of the VAGSs on different SiC substrates are analyzed and discussed.
A nonpolar SiC（1120） substrate has been used to fabricate epitaxial graphene （EG）. Two EGs with layer numbers of 8-10 （referred to as MLG） and 2-3 （referred to as FLG） were used as representative to study the substrate effect on EG through temperature-dependent Raman scattering. It is found that Raman lineshifts of G and 2D peaks of the MLG with temperature are consistent with that of free graphene, as predicted by theory calculation, indicating that the substrate influence on the MLG is undetectable. While Raman G peak lineshifts of the FLG to that of the free graphene are obvious, however, its lineshift rate （-0.016 cm-1/K） is almost one third of that （-0.043 cm-1/K） of an EG on 6H-SiC （0001） in the temperature range from 300 K to 400 K, indicating a weak substrate effect from SiC （1120） on the FLG. This renders the FLG with a high mobility around 1812 cm2.V-1 .s -1 at room temperature even with a very high carrier concentration about 2.95 × 10 ^13 cm-2 （p-type）. These suggest SiC （1120） is more suitable for fabricating EG with high performance.
We report on a demonstration of top-gated graphene field-effect transistors(FETs) fabricated on epitaxial SiC substrate.Composite stacks,benzocyclobutene and atomic layer deposition Al2O3,are used as the gate dielectrics to maintain intrinsic carrier mobility of graphene.All graphene FETs exhibit n-type transistor characteristics and the drain current is nearly linear dependence on gate and drain voltages.Despite a low field-effect mobility of 40 cm2/(V s),a maximum cutoff frequency of 4.6 GHz and a maximum oscillation frequency of 1.5 GHz were obtained for the graphene devices with a gate length of 1 μm.
MA PengJIN ZhiGUO JianNanPAN HongLiangLIU XinYuYE TianChunJIA YuPingGUO LiWeiCHEN XiaoLong
