Applying the Dirac equation to derive the transfer matrix for piecewise   constant potentials
  One propose a relativistic version of the transfer matrix method for an electron moving through a given number of rectangular barriers of arbitrary shape. It is shown that starting with the Dirac equation depending on the effective mass and a suitably chosen relativistic potential, one obtains a relativistic transfer matrix which takes the correct traditional form in the non-relativistic limit. 
Ion I. Cotaescu, Paul Gravila, Marius Paulescu