Published online by Cambridge University Press: 26 February 2011
We study the dark conductivity σ d, dark conductivity activation energy Ea and photoconductivity σ ph of a-Si:H,F/a-Si,Ge:H,F superlattices both perpendicular and parallel to the plane of the layers. In parallel transport, both the σ ph and σ d are dominated by the alloy layer characteristics with the superposition of carrier confinement quantum effects. In perpendicular transport, the σ d shows an interplay of quantum mechanical tunneling through the barriers and of classical thermal emission over the barrier layer and the σ ph is controlled by the decreasing absorption by the silicon barrier layer as the optical gap Eopt of the structure decreases.
We also found that the multilayer structure allows to grow lower gap a-Si,Ge:H,F alloys than achievable under the same deposition conditions for bulk materials. This stabilizing effect allowed us to study low-gap superlattice structures and extract information about these very low gap (<1.2 eV) a- Si,Ge:H,F alloys.