Electronic structure of hydrogen-terminated silicon surfaces [H-Si(111)] studied by two-photon photoemission

The surface and bulk electronic states of hydrogen-terminated Si(111)-(1 × 1) [H-Si(111)] were studied by two-photon photoemission (2PPE) spectroscopy. With the polarization and emission-angle dependence of the 2PPE spectra, five series of electronic structures for H-Si(111) can be identified as A, B, C, D, and E in the 2PPE spectra by fine tuning the exciting photon energy, hv, from 4.23 to 4.90 eV. For hv < 4.6 eV, peak A arises from a surface resonance at a 1.01 eV from E_F, and at the photon energy higher than 4.6 eV, peak A indicates photoemission from an intermediate state, corresponding to an image-potential state at 3.61 eV from EF. Other structures, B, C, and D arise from bulk states, while structure E occurs from an electronhole excitation process. This work has revealed the surface resonance and the image-potential state on H-Si(111) for the first time.