Subgap Absorption and Electrical Properties of Compositional Multilayers of a-Si:H and Alloys

ABSTRACTUrbach tails and midgap absorption, as determined by PDS, and temperature dependent coplanar and sandwich conductivity were systematically investigated on compositional multilayers of a-Si:H and its alloys with Ge and C, under the main aspect of a critical evaluation with respect to a possible existence of quantum size effects. Both electronic well and barrier widths were varied, with and without keeping the mean composition of the multilayers constant. Neither the overall dependences of the Urbach slopes, nor of the conductivity activation energies and room temperature αdark values are consistent with a quantization picture. Other effects, as imposing on each other the own sublayer's degree of structural disorder, and adjustment of the Fermi level by charge transfer, play a dominant role and may feign quantum size effects, if in a multilayer series only variation of the well widths is considered.