Comparison of a-Si1-xCx:H Layers Based on Methane, Di-, Tri- and Tetrasilylmethane as Feedstocks

Abstract

ABSTRACTUsing standard rf glow discharge deposition, we compare the properties of a-Si1-xCx:H films prepared with different carbon sources, namely methane and di-, tri- and tetrasilylme-thane (DSM, TSM and TetraSM). The optical bandgap EG was varied between 1.8 eV and 2.4 eV. All oua-Si1-xCx:H films exhibit low Urbach energies (EQ < 60 meV for EG< 2.0 eV) and low defect absorption, both determined by PDS. Using the silylmetha-nes as feedstocks, we do not find significant differences relative to our methane-based material. Independently of the carbon source material, the energy gap dependences of the film properties (photoconductivity, activation energy of the dark conductivity, Urbach energy and subbandgap defect absorption) show a distinct change around EG = 2.1 eV, which is interpreted as a consequence of structural changes with increasing carbon content.