Evidence for semiconductor-semiconductor interface states: Si(111) (2 × 1)-Ge

A direct correlation was found for the first time between theory and experiments on the localized electronic states at a semiconductor-semiconductor interface. The investigation involved synchrotron-radiation photoemission experiments and tight-binding calculations on Ge adatoms on cleaved Si substrates. The theoretically predicted interface states in a region 4-9 eV below the Fermi level were detected in the experimental spectra. These occupied states and their unoccupied counterparts have a fundamental influence on the localized one-electron transitions and on relevant heterojunction parameters in transport processes.