When graphene is interfaced with a semiconductor, a Schottky contact forms with rectifying properties. Different from a typical metal/semiconductor junction, the Schottky barrier height a the graphene/semiconductor junction can be directly controlled by an electric field, owing to the lack of interface states at the nonbonding graphene/semiconductor junction, and the readily tunable graphene Fermi level. However, graphene is also susceptible to the formation of ripples upon making contact with another material. Here, we report intrinsic ripple- and electric field-induced barrier fluctuations at the graphene semiconductor Schottky junction.
Chemical vapor deposited graphene is transferred onto both Si- and C-faces of SiC, as confirmed by Raman spectroscopy and STM imaging. Tunneling spectroscopy indicates that for graphene/C-SiC, the Dirac point is at 0.42 eV below EF while on the Si-face it is 0.35 eV above, a direct consequence of the larger work function at the Si-face. In addition, we observe spatial fluctuations in the Schottky barrier height caused by the intrinsic rippling at the graphene/SiC interface. The spacial variation of the Dirac energy directly follows the undulations of the ripples, exhibiting a Gaussian distribution with a full-width-at-half-maximum of 42 and 51 meV for graphene transferred on C- and Si-SiC, respectively. This result – in direct contrast to graphene/SiO2, where variation in the Dirac energy is not correlated to topographic variations, but to charge impurities in the SiO2 substrate – reflects an intrinsic effect inherent for graphene/semiconductor Schottky contacts.
Published in Nature Communications:
“Spatial fluctuations in barrier height at the graphene-silicon carbide Schottky contact“, S. Rajput, M. Chen, Y. Liu, Y. Y. Li, M. Weinert, and L. Li, Nature Communications 4, 2752 (2013).