Direct observation of localized unoccupied states by synchrotron radiation two-color resonant photoemission

Observation of localized unoccupied state in luminescent amorphous silicon-rich nitride films was reported by using the synchrotron radiation two-color resonant photoemission technique. The energy separation between the localized unoccupied state and top valence band was observed to shift from 2.4 to 1.8 eV while increasing the silicon richness. This observation is in agreement with the previously reported photoluminescence red-shift results. Moreover, it is found that the localized unoccupied states are strongly correlated with the SiN bonding configurations. Considering the microstructures (silicon platelets embedded into the amorphous silicon nitride environments) of these samples, it is believed that the localized unoccupied states would possible come from the surface region of silicon platelets.