  This paper investigates the problem of a relativistic Dirac half integer spin
free particle tunneling through a rectangular quantum-mechanical barrier. If
the energy difference between the barrier and the particle is positive, and the
barrier width is large enough, there is proof that the tunneling may be
superluminal. For first spinor components of particle and antiparticle states,
the tunneling is always superluminal regardless the barrier width. Conversely,
the second spinor components of particle and antiparticle states may be either
subluminal or superluminal depending on the barrier width. These results derive
from studying the tunneling time in terms of phase time. For the first spinor
components of particle and antiparticle states, it is always negative while for
the second spinor components of particle and antiparticle states, it is always
positive, whatever the height and width of the barrier. In total, the tunneling
time always remains positive for particle states while it becomes negative for
antiparticle ones. Furthermore, the phase time tends to zero, increasing the
potential barrier both for particle and antiparticle states. This agrees with
the interpretation of quantum tunneling that the Heisenberg uncertainty
principle provides. This study results are innovative with respect to those
available in the literature. Moreover, they show that the superluminal
behaviour of particles occurs in those processes with high-energy confinement.
