Electron-phonon coupling on strained Ge/Si(111)-(5×5) surfaces

Abstract

We investigate the structural and electronic properties of strained Ge/Si(111)-($5\ifmmode\times\else\texttimes\fi{}5$) surfaces by means of scanning tunneling microscopy and high-resolution angle-resolved photoemission spectroscopy. The homogeneous ($5\ifmmode\times\else\texttimes\fi{}5$) reconstructed overlayers are characterized by three electronic surface states, similar to the Si(111)-($7\ifmmode\times\else\texttimes\fi{}7$) surface. The dispersion of the dangling bond related surface state exhibits the same periodicity as that of the ($5\ifmmode\times\else\texttimes\fi{}5$) reconstruction. Moreover, a careful analysis of the shape and width of this surface state provides striking evidence of electron-phonon coupling at low temperatures. By considering the spectral function within a simple Debye model, we determine both the Debye energy and the electron-phonon coupling strength. The latter value is further confirmed by analyzing the temperature-dependent phonon broadening of the dangling bond related surface state linewidth.