An Ambipolar Virtual-Source-Based Charge-Current Compact Model for Nanoscale Graphene Transistors

A compact physics-based ambipolar-virtual-source (AVS) model is presented that describes carrier transport in both unipolar and ambipolar regimes in quasi-ballistic graphene field-effect transistors (GFETs). The transport model incorporates two separate virtual sources for electrons and holes and is supplemented by a self-consistent channel-charge-partitioning model valid from drift-diffusive to ballistic transport conditions. The model comprehends the asymmetry introduced by different contact resistances for electrons and holes. The AVS model has a limited number of parameters, most of which have a physical meaning and can easily be extracted from device characterization. The model has been extensively calibrated with experimental dc I-V and s-parameter measurements of devices with gate lengths from 650 to 40 nm. This has allowed the scaling of mobility and VS source injection velocity of carriers with gate length to be investigated for the first time. The new compact model yields continuous currents and charges and can easily be used in the design and analysis of circuits and systems implemented with GFETs.