Valence band offset and interface stoichiometry at epitaxial Si3N4/Si(111) heterojunctions formed by plasma nitridation

Ultrathin β-Si3N4(0001) epitaxial films formed by N2-plasma nitridation of Si(111) substrates have been studied by photoelectron spectroscopy using synchrotron radiation. The valence band offset at the β-Si3N4/Si interface was determined by valence-band photoelectron spectra to be 1.8 eV. Furthermore, the Si 2p core-level emissions were analyzed for nitride (Si4+) and subnitride (Si3+ and Si+) components to characterize the interface stoichiometry. In contrast to the interfaces formed by ammonia thermal nitridation and N2-plasma nitridation at room temperature, the interface formed by N2-plasma nitridation at high substrate temperature is very close to subnitride free with an abrupt composition transition.