Localized-State-Density Distribution in Post-Hydrogenated CVD Amorphous Silicon

Abstract

Chemically-vapor-deposited amorphous Si films containing no bonded hydrogen were hydrogenated by hydrogen plasma annealing. The remarkable reduction of the localized state density in the mobility gap produced by the hydrogenation was confirmed quantitatively by the field-effect technique. The localized state density near the center of the mobility gap was reduced to less than 1×1018cm-3eV-1, and the widths of the tail states below the conduction band and above the valence band were also decreased by the hydrogenation. An energy band model involving an electron trapping level ∼0.12 eV below the conduction band and hole trapping levels ∼0.35 and ∼0.20 eV above the valence band is proposed, and the ∼1.25 eV- and ∼1.10 eV-luminescence peaks are explained in terms of the radiative transitions between these trapping states.