Thermal conductivity of thermally annealed nanocrystalline silicon film grown by PECVD technique

Nanocrystalline silicon films (nc-Si) have been shown to have significantly lower lattice thermal conductivity than its micro-polycrystalline counterparts. However, it is essential for high temperature applications, such as thermoelectrics, to maintain their low thermal conductivity characteristics upon annealing, which may depend on the details of film preparation techniques. We investigate the effect of postdeposition thermal annealing on the thermal conductivity of nc-Si films prepared by plasma-enhanced chemical vapor deposition (PECVD) . After annealing the PECVD nc-Si at 600°C for two hours, its thermal conductivity is increased two-fold, reaching 1.86 W/mK at 300K, however this value is lower than similarly annealed nc-Si films prepared by the hot-wire chemical vapor deposition technique by a factor of 2.5. Our structural characterizations reveal that after annealing, the average crystalline grain size of PECVD nc-Si is increased to ~4.6 nm from the as-grown value of 3 nm. We discuss the possible cause of the low lattice thermal conductivity of PECVD nc-samples in terms of grain boundary scattering.