Metal and Semiconductor Overlayers on Bi₂Sr₂CaCu₂O_8+δ

Abstract

We have studied the electronic properties of interfaces formed by Al, Au, Bi, CdTe, Cu, Ge, Pb and Sn with cleaved single crystals and with epitaxial thin films of Bi₂Sr₂CaCu₂O_8+δ using angle-integrated photoemission spectroscopy with synchrotron radiation. Measurements were performed over a wide range of photon energies, from 16 eV to 160 eV, yielding valence band, core level and resonant photoemission spectra which, in combination, provided detailed information about the interfaces. The resonant photoemission spectra give clear evidence of changes in the electronic structure associated with the CuO₂-planes of the superconductor as a function of adsorbate film thickness. All the materials deposited on the superconductor induce some changes in the weakly-bound electronic states arising from the CuO₂-planes. Al, Cu, Ge and Sn form strongly reactive interfaces, whereas Bi, CdTe and Au are less reactive. Pb is an intermediate case since it forms a monolayer of insulating PbO at the interface. The system CdTe/Bi₂Sr₂CaCu₂0_8+δ . is an interesting example of a less reactive interface between a semiconductor and a superconductor. In this paper we focus on Au overlayers, which are suitable for use as metallic contacts in devices.