Tunneling of Dirac electrons through spatial regions of finite mass

We study the tunneling of chiral electrons in graphene through a region where the electronic spectrum changes from the usual linear dispersion to a hyperbolic dispersion, due to the presence of a gap. It is shown that contrary to the tunneling through a potential barrier, the transmission of electrons is, in this case, smaller than one for normal incidence. This mechanism may be useful for designing electronic devices made of graphene.