Bulk electronic structure of germanium studied with angle-resolved photoemission

The cleaved Ge(111)2×{}1 surface has been studied with angle-resolved photoemission for photon energies between 10 and 35 eV. Spectra were recorded for the polarization vector of the light perpendicular and parallel to the (11{}0) mirror plane, allowing the separation of initial states of odd and even parity, respectively. A detailed analysis of the spectra is made for several free-electron final bands. Strong features in off-normal spectra are found to correspond to a free-electron-like primary-cone final band, and several weaker secondary-cone contributions are also observed. A comparison with calculated spectra is made for normal emission and several similarities are observed between theoretical and experimental spectra, especially for transitions not described by free-electron bands. It is suggested that the transitions contributing to the emission in the measured spectra have pronounced matrix elements mainly when the final states are close to free-electron bands, but that other final bands, which must be associated with the real band structure, contribute as well.