Midinfrared studies of the contact region at superconductor-semiconductor interfaces

InAs quantum wells (QWs) have been used as weak links in many recent studies 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 used midinfrared spectroscopy to investigate the superconductor/semiconductor contact region. The remnant intersubband absorption we observe in Nb-clad InAs shows that the superconductor/InAs interface produced some confinement of electrons in the InAs. This confinement is, however, consistent with phase coherent transport in the InAs. We find no evidence for charge transfer from the superconductor to the InAs on cooling below the critical temperature of Nb. (C) 2000 American Institute of Physics. [S0003-6951(00)03502-6].