Time dependence of transmission in semiconductor superlattices
  Time delay in electron propagation through a finite periodic system such as a semiconductor superlattice is studied by direct numerical solution of the time-dependent Schr\"odinger equation. It is found that addition of an anti-reflection coating significantly reduces the time delay, in addition to increasing the transmissivity. 
C. N. Veenstra, W. van Dijk, D. W. L. Sprung, J. Martorell