Ph. Mavropoulos, N. Papanikolaou, M. Freyss, R. Zeller, and P.H. Dederichs

We investigate the importance of Metal-induced Gap States for the tunneling of metal electrons through insulator films. By introducing an imaginary part k to the wavevector in order to describe the decay of the wavefunction in the insulator, we obtain the complex band structure in the gap region. The spectrum of the decay parameters k is calculated for the semiconductors Si, Ge, GaAs, and ZnSe. In most cases, for large enough film thicknesses the tunneling is dominated by states of normal incidence on the interface; possible exceptions are considered. Based on our conclusions, we discuss the spin-dependent tunneling in Fe/Semiconductor/Fe (001) junctions.