Recombination Time in Drift-Diffusion Models of Graphene Field-Effect Transistors

Graphene field-effect transistors (GFETs) have been extensively studied for electronic applications such as sensors and radiofrequency. Several physics-based models have been developed to explain carrier transport in these transistors, but the approach for introducing carrier generation-recombination is still a topic of debate. This work presents a method for calculating the net recombination rate, which is then applied to a self-consistent Poisson-drift-diffusion GFET model. The method is adapted from semiconductor physics to suit the two-dimensional nature of graphene. The study also explores how recombination time affects carrier transport when both electrons and holes are present in the graphene channel, which mainly occurs when the transistor is biased near the Dirac point. The results confirm that a single quasi-Fermi level for electrons and holes is a good approximation when recombination times are sufficiently small. Additionally, the study finds that the single level approximation requires lower recombination times in short channel GFETs.