Measurement of transversal ambipolar diffusion coefficient in microcrystalline silicon

Transport properties of microcrystalline silicon (μc-Si) are analyzed by diffusion-induced time resolved microwave conductivity (DTRMC), a new contactless method. Computer simulations show that with this method the ambipolar diffusion coefficient of carriers in the transversal direction, even for thin layers (typically 100 nm), can be determined. Ex situ measurements are made on several samples with various μc-Si thicknesses deposited in the same conditions. The evolution of transport parameters with layer thickness is correlated with the inhomogeneity of the layer structure detected by ellipsometry. In particular, we demonstrate that the presence of an amorphous interface between the substrate and μc-Si can be the main limiting factor of transversal transport.