Optical detection of the superconducting proximity effect: Raman scattering on Nb/InAs

Raman scattering on InAs coated with 60 to 100Å thick Nb films (Tc=2.5 to 5K) is studied. The Nb films, sputtered ontoin-situ ion-etched n+-InAs (1.2×1019cm−3) are flat to ∼5Å. The low-frequency coupled plasmon-phonon Raman mode (L_) associated with bulk InAs is centered at 221 cm−1. The forbidden LO phonon at 237cm−1, associated with the surface charge accumulation region (CAR), is observed because the thickness of the surface CAR is less than the Thomas-Fermi screening length. As the temperature is reduced below Tc the magnitude of the LO phonon mode intensity, relative to that of the L_mode, increases by more than 40%