Majority and minority carrier mobility behavior and device modeling of doped CVD monolayer graphene transistors

Abstract

Wafer-scale graphene synthesized by Chemical Vapor Deposition (CVD) has the potential to enable numerous advanced device and system capabilities [1–3]. The typical reported carrier mobility of CVD graphene is significantly lower than exfoliated or on-SiC material due potentially to different impurity/doping levels and material quality. Elucidating the potential carrier scattering sources in metal catalyzed CVD graphene is essential for realizing high mobility material for both holes and electrons. We constructed field effect transistors using Cu catalyzed LPCVD synthesized p-type doped monolayer graphene and used direct electrical measurements under ambient and vacuum conditions to analyze some important physical aspects of the majority and minority carrier mobility behavior. We measured a dependency between shifting of the Dirac Point directed towards neutral levels under soft vacuum/annealing conditions and an increase in the extracted low-field carrier mobility. Reduction in the effective p-type “doping” of the graphene results in an increase of the carrier mobility of both the minority electrons and majority holes, with a stronger majority carrier dependency. The measured I–V characteristics of the devices are modeled (in the scattering limited regime) using a simple drift/diffusion model implemented in a continuum simulator. Using this model, the effective doping density, carrier concentration, and mobility are extracted for electrons and holes. Analysis of the energy dependency of the carrier mean-free-path for back-scattering, suggests that the hole mobility in this CVD material is limited by large levels of Coulomb scattering, whereas the electron mobility is limited by a combination of both Coulomb and other shorter-range scattering.