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Abstract
A semiempirical model describing the influence of interface states on characteristics of gate capacitance and drain resistance versus gate voltage of top gated graphene field effect transistors is presented. By fitting our model to measurements of capacitance–voltage characteristics and relating the applied gate voltage to the Fermi level position, the interface state density is found. Knowing the interface state density allows us to fit our model to measured drain resistance–gate voltage characteristics. The extracted values of mobility and residual charge carrier concentration are compared with corresponding results from a commonly accepted model which neglects the effect of interface states. The authors show that mobility and residual charge carrier concentration differ significantly, if interface states are neglected. Furthermore, our approach allows us to investigate in detail how uncertainties in material parameters like the Fermi velocity and contact resistance influence the extracted values of interface state density, mobility, and residual charge carrier concentration.
Highlights
The inherent high charge carrier velocity in graphene establishes its potential use in high frequency electronics
While interface traps influence the capacitance level [Fig. 3(d)], the charging of bulk oxide traps affects the value of the gate voltage for a given position of the Fermi-level [Eq (14), Fig. 4(b)]
When the bulk oxide traps are filled by negative charge in the period of the measurement cycle the Dirac point, VDirac, is shifted to higher voltage, when sweeping the gate voltage back from Vg 1⁄4 3 to À3 V
Summary
The inherent high charge carrier velocity in graphene establishes its potential use in high frequency electronics. The carrier mobility of graphene has been extracted by different methods, some of which require additional structures in the form of Hall bars and van der Pauw structures.. A hysteresis effect is often observed in capacitance and drain resistance characteristics for a dual sweep of the gate voltage. This indicates that charge carriers are captured in oxide traps within tunneling distance from the graphene/oxide interface. The mobility, l, will be significantly underestimated, since the conductivity, r, is given by r 1⁄4 qlnG This expression is valid when the effect of charge accumulation near the edges can be neglected. Our approach has the advantage that we can examine limits set by uncertainties of material parameters such as Fermi velocity, capture and emission rates of charge carriers, and mobilities for electrons and holes
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Schedule a callMore From: Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena
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