Abstract
High-k materials such as Al2O3 and HfO2 are widely used as gate dielectrics in graphene devices. However, the effective work function values of metal gate in graphene FET are significantly deviated from their vacuum work function, which is similar to the Fermi level pinning effect observed in silicon MOSFETs with high-k dielectric. The degree of deviation represented by a pinning factor was much worse with HfO2 (pinning factor (S) = 0.19) than with Al2O3 (S = 0.69). We propose that the significant pinning-like behaviors induced by HfO2 are correlated with the oxygen exchange reactions occurred at the interface of graphene and HfO2.
Highlights
Graphene has received considerable attention because of its extraordinary electrical and physical properties, such as its high carrier mobility, excellent thermal stability, and top-down processing compatibility[1,2,3]
The physical scaling of gate dielectric has been the primary focus of study in the gate stack research for graphene because it is difficult to form a thin gate dielectric on graphene using atomic layer deposition (ALD) process because graphene does not have enough dangling bonds to initiate the chemical reactions for ALD
We found that the effective work function values of metal gates on the high-k dielectric and graphene stack are significantly deviated from the vacuum work function, which is similar to the Fermi level pinning effect of a metal gate/high-k dielectric stack in silicon metal–oxide–semiconductor field-effect transistors (MOSFETs)
Summary
We can conclude that the strong Fermi level pinning observed for the GFETs fabricated with the HfO2 gate dielectric is due to the inhibition of electron doping, which occurs via counter-charge generation at the dielectric/graphene interface due to the interfacial oxygen accumulation. This mechanism is quite different from the original Fermi level pinning mechanism because the chemically induced charges are limiting the movement of Fermi level of graphene rather than the defect states
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