  In this paper we study scattering of two-dimensional massless Dirac fermions
by a potential that depends on a single Cartesian variable. Depending on the
energy of the incoming particle and its angle of incidence, there are three
different regimes of scattering. To find the reflection and transmission
coefficients in these regimes, we apply the Wentzel-Kramers-Brillouin (WKB),
also called semiclassical, approximation. We use the method of comparison
equations to extend our prediction to nearly normal incidence, where the
conventional WKB method should be modified due to the degeneracy of turning
points. We compare our results to numerical calculations and find good
agreement.
