In-plane Thermal Conductivity of PECVD Nanocrystalline Silicon Films

Nanocrystalline silicon (nc-Si) is of interest for high temperature thermoelectric (TE) devices due to its low thermal conductivity which strongly depends on grain size and crystalline orientation. We have recently reported out-of-plane thermal conductivity of nanocrystalline films prepared by plasma-enhanced chemical-vapor deposition (PECVD) method over a temperature range of 80K to 800K. We found that PECVD nc-Si films tend to grow in columnar grain-structure. Here, we will report the surface and grain boundary effects on the in-plane thermal conductivity of PECVD nc-Si films between 100 and 550K using the 3ω-Völklein method. The in-plane thermal conductivity measurements are compared with the out-of-plane thermal conductivity results. We discuss the possible cause of the low thermal conductivity of PECVD nc-Si films in terms of grain boundary scattering.