Potential barriers and hall mobility of polycrystalline silicon

Grain boundaries play a dominant role in understanding the properties of polycrystalline silicon and make it difficult to analyse the results. By illuminating the samples with light of approximately solar intensity, the potential barriers at the grain boundaries can be removed and thus approach single crystal behaviour. When the barriers are removed, the mobility between 200 and 400 K is found to vary as $\text{T}{}^{\mathrm{-2}}$, which is the dependence observed in single crystals for the same order of magnitude of doping. The free carrier concentration of 5 × 10¹⁵ cm⁻³ is not affected by illumination. The room temperature mobility in 1 mm grain size material after barrier elimination by light is 900 cm² V⁻¹ s⁻¹. The theory of Hall mobility in polycrystalline silicon which explains these observations has been examined.