We measure drift velocity in monolayer graphene encapsulated by hexagonal boron nitride (hBN), probing its dependence on carrier density and temperature. Due to the high mobility (>5 × 104 cm2/V/s) of our samples, the drift velocity begins to saturate at low electric fields (∼0.1 V/μm) at room temperature. Comparing results to a canonical drift velocity model, we extract room-temperature electron saturation velocities ranging from 6 × 107 cm/s at a low carrier density of 8 × 1011 cm-2 to 2.7 × 107 cm/s at a higher density of 4.4 × 1012 cm-2. Such drift velocities are much higher than those in silicon (∼107 cm/s) and in graphene on SiO2, likely due to reduced carrier scattering with surface optical phonons whose energy in hBN (>100 meV) is higher than that in other substrates.
Keywords: boron nitride; drift velocity saturation; graphene; high field; phonon scattering.