Variability of graphene mobility and contacts: Surface effects, doping and strain

It is well known that devices based on chemical vapor deposited (CVD) graphene exhibit substantial variability of their electrical properties [1]. However, the sources of such variability and how they might be controlled remain poorly understood. Here, we methodically investigate variability of CVD graphene field-effect transistors (GFETs) transferred with three polymer scaffolds: PMMA, polycarbonate (PC), and a PC/PMMA bilayer (PC in contact with graphene). We find that the polymer/graphene mechanical interaction during transfer and the presence of surface residues induce changes in graphene roughness (up to ~0.2 nm), doping concentrations (up to ~2.5×10¹² cm^-2) and strain levels (up to ~0.2%) between the polymer scaffolds used. We uncover that a combination of smaller strain and doping from the PC/PMMA scaffolds ultimately yields the lowest variability of contact resistance (R_c) and mobility (μ).