1. For one-particle tunneling between normal metal and a superconductor, show qualitatively how the coherence factors and drop out from the expression for the tunneling current.

For one particle tunneling, one has to create single particle excitations in a superconductor. It involves electron state as well as hole state in such a way that the coherence factors and drop out from the expression for the tunneling current.

2. What is the semiconductor model of excitations in the superconductors ?

In the semiconductor model the superconducting gap is treated as the band gap of the semiconductor. Howevere, one must remember that an elementary excitation in a superconductor is a linear combination of states above as well as below the superconducting gap.