Band-tail photoluminescence in nanocrystalline Si

The characteristic subgap photoluminescence (PL) observed in nanocrystallin e Si films was found to shift to higher energies with increasing optical ga p and decreasing crystallite size. This behavior, along with the temperatur e dependence of the PL, is consistent with transitions between band-tail st ates in the energy gap of the crystallites. The PL bandwidth is too broad t o be explained by the tail width as deduced from the temperature behavior. Hence, the broadening is ascribed to electron-phonon coupling, while the re lated Stokes shift was found to increase with decreasing crystallite size, possibly due to decreasing exciton size. (C) 2000 American Institute of Phy sics. [S0003-6951(00)03527-0].