Cavity-enhanced optical Hall effect in epitaxial graphene detected at terahertz frequencies

Highlights: • Cavity-enhanced THz optical Hall effect reveals transport properties of graphene. • Type of charge carriers, their mobility, density and effective mass were determined. • Monolayer graphene has p-type doping, while multilayer graphene – n-type doping. • Increased hydrophobicity of multilayer graphene explains its n-type conductivity. - Abstract: Cavity-enhanced optical Hall effect at terahertz (THz) frequencies is employed to determine the free charge carrier properties in epitaxial graphene (EG) with different number of layers grown by high-temperature sublimation on 4H-SiC(0001). We find that one monolayer (ML) EG possesses p-type conductivity with a free hole concentration in the low 10¹² cm⁻² range and a free hole mobility parameter as high as 1550 cm²/Vs. We also find that 6 ML EG shows n-type doping behavior with a much lower free electron mobility parameter of 470 cm²/Vs and an order of magnitude higher free electron density in the low 10¹³ cm⁻² range. The observed differences are discussed. The cavity-enhanced THz optical Hall effect is demonstrated to be an excellent tool for contactless access to the type of free charge carriers and their properties in two-dimensional materials such as EG.