This is a minor generalization of the plot shown in Fig. 2a of . It shows the transmission coefficient for a plane wave incident on a barrier of height . The parameters for graphene given in that paper have been used: Dirac speed , energy , Fermi momentum ; the width of barrier ranges from and lies between .
M. I. Katsnelson, K. S. Novoselov, and A. K. Geim, "Chiral Tunneling and the Klein Paradox in Graphene," Nature Phys., 2, 2006 pp. 620–625.