Midinfrared studies of the contact region at superconductor-semiconductor interfaces

InAs quantum wells (QWs) have been used as weak links in many recent studie s of novel superconductor-normal metal-superconductor junctions. The degree of coupling between the superconducting electrodes depends sensitively on both the superconductor/InAs interface and the QW material in the weak link , factors that are difficult to separate in dc transport studies. Here we u sed midinfrared spectroscopy to investigate the superconductor/semiconducto r contact region. The remnant intersubband absorption we observe in Nb-clad InAs shows that the superconductor/InAs interface produced some confinemen t of electrons in the InAs. This confinement is, however, consistent with p hase coherent transport in the InAs. We find no evidence for charge transfe r from the superconductor to the InAs on cooling below the critical tempera ture of Nb. (C) 2000 American Institute of Physics. [S0003-6951(00)03502-6] .