Observation of the superconducting proximity effect in Nb/InAs andNbNx/InAsby Raman scattering

Abstract

High-quality thin Nb and NbN films ͑60-100 Å͒ are grown on ͑100͒ n ϩ-InAs (nϭ10 19 cm Ϫ3) substrates by dc-magnetron sputter deposition. Studies of the electronic properties of interfaces between the superconductor and the semiconductor are done by Raman scattering measurements. The superconducting proximity effect at superconductor-semiconductor interfaces is observed through its impact on inelastic light scattering intensities originating from the near-interface region of InAs. The InAs longitudinal optical phonon LO mode (237 cm Ϫ1) and the plasmon-phonon coupled modes L Ϫ (221 cm Ϫ1) and L ϩ ͑1100 to 1350 cm Ϫ1), for n ϩ ϭ1ϫ10 19 Ϫ2ϫ10 19 cm Ϫ3 are measured. The intensity ratio of the LO mode ͑associated with the near-surface charge accumulation region, in InAs͒ to that of the L Ϫ mode ͑associated with bulk InAs͒, is observed to increase by up to 40% below the superconducting transition temperature. This temperature-dependent change in light scattering properties is only observed with high quality superconducting films and when the superconductor and the semiconductor are in good electrical contact. A few possible mechanisms of the observed effect are proposed.

Optical and transport properties of ultrathin NbN films and nanostructures

“…6 The reason for the discrepancy is not clear. However, we note that assuming a lower effective electron mass, as it is expected in nitrides, 19 would increase the discrepancy. Theoretical estimates of the freeelectron concentration in NbN vary from 2.39ϫ 10 29 m −3 ͑Ref.…”

Construction of a Cantilever-Andreev-Tunneling rig and its applications to superconductors

“…This observation is not unusual and we stress that Nb can have different superconducting properties depending on the cleanness of the material. 27 MgB 2 has drawn great deal of attention due to fundamental interest and application potential. It is recognized as the first superconductor which distinctly exhibits two gaps, as shown by a variety of different experiments 8,9,28,29 with supporting theories.…”

Investigations of proximity-induced superconductivity in the topological insulator Bi2Te3 by microRaman spectroscopy

“…Raman scattering has been used to investigate the superconducting gap 19 – 22 as well as proximity-induced superconductivity in semiconductor-superconductor hybrid structures 23 – 25 . Superconductivity in an investigated material is reflected in Raman spectra as changes in the frequency and linewidth of certain phonon modes as the temperature drops below T c .…”