Semiconductor/molecule transport junctions: An analytic form for the self-energies

We have derived an approximate analytic expression for the spectral density of a simple model of a semiconductor/molecule junction. The semiconductor is considered as a tight-binding one-dimensional chain with periodic boundary conditions, and either bond or site-energy alternation, to mimic a two-band system. Using the simplest representation for an atomic or molecular site we obtain a spectral density whose main physical and mathematical features are independent of the alternation pattern. Our model can be applied to the description of transport properties in many complex junctions. Here, we have explored its simplest consequences in the calculation of the transmission coefficient for a junction consisting of a semiconductor electrode, a molecular site and a metal electrode.