  Variable-field Hall measurements were performed on epitaxial graphene grown
on Si-face and C-face SiC. The carrier transport involves essentially a
single-type of carrier in few-layer graphene, regardless of SiC face. However,
in multi-layer graphene (MLG) grown on C-face SiC, the Hall measurements
indicated the existence of several groups of carriers with distinct mobilities.
Electrical transport in MLG can be properly described by invoking three
independent conduction channels in parallel. Two of these are n- and p-type,
while the third involves nearly intrinsic graphene. The carriers in this
lightly doped channel have significantly higher mobilities than the other two.
