Si and SiGe Nanowires: Fabrication Process and Thermal Conductivity Measurement by 3ω-Scanning Thermal Microscopy

We have grown various samples of Si and SiGe nanowires (NWs), either by a classical vapor-liquid-solid (VLS) process or by chemical etching, to measure their thermal conductivity and thus evaluate their efficiency for thermoelectrics applications. To do so, we have chosen a 3 omega-Scanning Thermal Microscopy (SThM) imaging technique which is until now the only method able to perform topographical and thermal measurements simultaneously on an assembly of individual NWs, leading to a statistical value of their thermal conductivity. A size effect is clearly observed on Si NWs: 50 nm diameter NWs offer a reduced thermal conductivity in comparison with 200 nm diameter or even larger NWs. On the contrary, the thermal conductivity of SiGe NWs is widely reduced in comparison with the SiGe bulk value; even for large diameters, bigger than Si NWs ones. We discuss our results, comparing them with thermal conductivity values from the literature obtained by other measurement methods or models.