Andreev-reflection in semiconductor-coupled superconducting weak-links

We investigated the carrier transport through highly doped n - InSb-films sandwiched between two superconducting lead electrodes. The measured I(V)- and dV/dI(V)-characteristics show a very clear subharmonic gap structure (SGS) and an excess current, indicating the occurrence of multiple Andreev-reflection between the two semiconductor-superconductor interfaces. For the theoretical background we consult the theory of Octavio et al. (OTBK-model). We show that the application of this theory leads to some difficulties. According to this we propose some modifications, which in our opinion give a better description of the real situation in such contacts. We calculated the I(V)- and dV/dI(V)-characteristics of junctions with dissimilar barrier strength at the two interfaces as well as such for different superconductors, and compare these results with the experimental observations. We studied the influence of electromagnetic radiation on the junctions properties experimentally as well as theoretically for frequencies ranging in the classical limit. Moreover we evaluate the temperature dependence of the excess current, compare it with theoretical results and give an estimation of the barrier strength. The critical current is studied in dependence on the temperature and in comparison with calculations of Kuprianov and Lukichev (KL-theory), as well as under rf-application. (orig.)