Hall-Effect Studies on Microcrystalline Silicon with Different Structural Composition and Doping

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Abstract
Hall-effect experiments on -type microcrystalline silicon samples with a wide range of structural composition and doping have been performed. For highly doped samples the conductivity Σ and the mobility μ show a non-singly activated behaviour while the carrier density is almost temperature independent. The comparison of the carrier density with the phosphorous concentration in conjunction with the conductivity gives strong evidence that the Hall-effect data have to be corrected with the crystalline volume fraction Xc. Furthermore, the increase of the mobility with Xc, which is linked in our case to the grain size, can be explained when the length of the transport paths is taken into account. Our results will be discussed in the framework of different transport models. It is concluded that transport in μc-Si:H can not be explained in terms of thermionic emission over barriers with a well defined barrier height; instead a distribution of barrier heights have to be considered. A transport model is suggested where μc-Si:H is viewed as an interconnected network.