Microcrystalline silicon -: Relation of transport properties and microstructure

Understanding of transport in hydrogenated microcrystalline silicon (mu c-Si:H) is difficult due to its complicated microstructure (grains, grain boundaries, amorphous tissue). mu c-Si:H layers often exhibit preferential orientation leading to transport anisotropy. Furthermore, specific mu c-Si:H growth features lead to the thickness dependence of the structure and properties. mu c-Si:H incubation layer was studied by AFM with conductive cantilever measuring simultaneously morphology and local conductivity maps with submicron resolution. Clear identification of Si crystallites (with size of few tens of nanometers) is demonstrated. The crystalline fraction at the surface may be easily evaluated. For the charge collection in solar cells we need to study transport perpendicular to the substrate. Measurement of frequency spectra of A.C, conductivity is introduced as a new tool which can exclude the influence of contact barriers in sandwich geometry and can be used for finding the "true" conductivity perpendicular to the substrate. Using this technique transport anisotropy in some mu c-Si:H samples was clearly demonstrated. Finally, it is shown how the transport properties change with growing mu c-Si:H thickness and how these changes correlate with the structure observed by AFM.