Thermoelectric properties of SiGeSn microdevices

• Applicants: Dan Buca, Ph.D.; Professor Giovanni Capellini, Ph.D., since 5/2024; Professorin Dr. Inga Fischer
• Subject Area: Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 537127697

Thermoelectrics (TE) holds great potentiality for the development of green information technology, as it can provide energy harvesting and thermal control with direct heat-electricity conversion. However, current materials are difficult to integrate in large scale production, or their performance is too low around room temperature. To this aim, the use of tin (Sn)-based alloys with Si and Ge is of great interest, as it can bring CMOS-integrated TE with qualitatively better performance with respect to SiGe. SiGeSn material system has been in the spotlight recently due to its application in lasers thanks to possible direct bandgap, and these developments are supported by epitaxial growth techniques for high-quality materials. Its TE application is nonetheless little explored and confined to amorphous and polycrystalline materials, that may not be suitable for optoelectronic CMOS devices. Our recent results have shown that thermal conductivity in high-quality GeSn epilayers can be as low as in amorphous GeSn, a desired feature for TE performance. Therefore, we propose an investigation of the SiGeSn alloys for its use in thermoelectric devices. Based on state-of-the-art growth facilities with wafer-scale Chemical Vapour Deposition, we propose to characterize the alloy thermoelectric properties depending composition and doping. The critical issue in the optimization of semiconductors for TE is to reduce the thermal conductivity due to phonon transport; we aim to address this topic using different strategies, that leverage on the expertise of the Applicants: the role of composition in ternary alloys; the effect of nanostructuring of the material, for example with the reduction to 1-dimensional transport; the control of the phonon transport in multilayers. The target is a detailed evaluation of the various material parameters affecting TE properties in simple devices. Beside these technological steps, we will develop advanced experimental techniques for the study of heat transport. In particular, we will go beyond standard electrical and optical methods, and assess the validity of mapping system at nanoscale (scanning probe microscopy) and of combined spectroscopy methods. The results from this research will build a relevant cluster of knowledge and expertise in a field crucial in the development of energy materials which are environmentally friendly and resilient to geo-political crises.

• DFG Programme: Research Grants
• Ehemaliger Antragsteller: Davide Spirito, Ph.D., until 5/2024