• nanomaterials
• heat transport
• thermoelectrics
• GeSn
• thermal conductivity
• 3-omega method

Thermoelectric (TE) effects offer an interesting perspective for the direct solid-state conversion of heat in electrical energy, and vice versa.
However, large-scale diffusion of TE devices is hindered by the low conversion efficiency and high cost of existing TE materials. Therefore, in the last few decades, research has focused on searching new materials and new strategies to improve TE efficiency and reduce fabrication costs. Typically, conversion efficiency can be enhanced by reducing the thermal conductivity of the material, for example using nanostructured materials or alloys.
In this thesis, I investigate the potential of GeSn, a novel promising alloy that could become the core of a future Si-compatible thermoelectric technology. GeSn alloys have been developed over the past decade with the target of implementing optoelectronic devices based on Si-compatible group-IV materials, and poses non-trivial challenges due to the intrinsic instability of GeSn towards segregation. Interestingly, GeSn is known to exhibit excellent electrical conductivity and is expected to have a low thermal conductivity.
As a first enabling step towards thermoelectric applications, the purpose of my work is to measure the thermal conductivity of epitaxial GeSn thin films at various concentrations of tin content, in order to quantify the reduction in thermal conductivity due to alloy scattering.
The technique adopted for the measurements is the “3-omega” method, a reliable and accurate electrothermal technique based on the detection of the third harmonic voltage generated across a thin metal wire deposited onto the specimen, when an alternating current is applied.
Experimental data confirms the expected reduction in the thermal conductivity of GeSn as a function of the concentration of Sn. These results constitute a promising starting point for further investigations of thermoelectric properties of GeSn alloys.