Interface formation of semiconductors with high-$T_c$ superconductors: ${\mathrm{G}\mathrm{e}/\mathrm{L}\mathrm{a}}_{1.85}$${\mathrm{Sr}}_{0.15}$${\mathrm{CuO}}_4$

Inverse photoemission has been used to probe the microscopic evolution of the semiconductor/superconductor interface ${\mathrm{G}\mathrm{e}/\mathrm{L}\mathrm{a}}_{1.85}$ ${\mathrm{Sr}}_{0.15}$ ${\mathrm{CuO}}_4$. We find little or no reaction until the Ge coverage reaches 1 Å and that the reaction is quickly saturated when the nominal coverage reaches Å6 Å. The reaction is characterized by the reduction of the $\mathrm{Cu} 3d-\mathrm{O} 2p$ antibonding electronic states straddling the Fermi level and the shift of $\mathrm{La} 4f \mathrm{and} 5d$ empty-state features toward $E_F$. Large apparent electron mean free paths deduced from the attenuation of La peaks suggest cluster and island formation in the ${\mathrm{G}\mathrm{e}/\mathrm{L}\mathrm{a}}_{1.85}$ ${\mathrm{Sr}}_{0.15}$ ${\mathrm{CuO}}_4$ interface.