Temperature Dependence of Structure, Transport and Growth of Microcrystalline Silicon: Does Grain Size Correlate with Transport?

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Abstract
The temperature dependence of the growth, structure and transport of plasma-deposited microcrystalline and polycrystalline silicon films have been investigated over the temperature range of 50°C to 350°C. While low substrate temperature yields small grain sizes as expected, high temperature also tends to suppress the grain growth, contrary to the normal behavior observed in thermal CVD (chemical vapor deposition) where crystallinity grows with temperature. In fact, the highest temperature of 350°C corresponds to the lowest degree of crystallinity. Furthermore, it is found that, unlike the polycrystalline Si prepared by thermal CVD, the transport properties of the Si films do not necessarily correlate with the grain size or structural defects. While the largest average grain size of 800–1000 Å was obtained at 200°C, the highest Hall mobility and conductivity were obtained near 250°C, which corresponds to a material with smaller grains and an abundance of voids.