Thermoelectric properties on Ge/Si1−xGex superlattices

Ferre Llin, Lourdes (2014) Thermoelectric properties on Ge/Si1−xGex superlattices. PhD thesis, University of Glasgow.

Abstract

Thermoelectric generation has been found to be a potential field which can be exploited in a wide range of applications. Presently the highest performances at room temperature have been using telluride-based devices, but these tech- nologies are not compatible with MEMs and CMOS processing. In this work Silicon and Germanium 2D superlattices have been studied using micro fabri- cated devices, which have been designed specifically to complete the thermal and electrical characterization of the different structures.
Suspended 6-contact Hall bars with integrated heaters, thermometers and ohmic contacts, have been micro-fabricated to test the in-plane thermoelectric properties of p-type superlattices. The impact of quantum well thickness on the two thermoelectric figures of merit, for two heterostructures with different Ge content has been studied.
On the other hand, etch mesa structures have been presented to study the cross-plane thermoelectric properties of p and n-type superlattices. In these experiments are presented: the impact of doping level on the two figures of merit, the impact of quantum well width on the two figures of merit, and the more efficient reduction of the thermal conductivity by blocking phonons with different wavelengths. The n-type results showed the highest figures of merit values reported in the literature for Te-free materials, presenting power factors of 12 mW/K2 · m, which exceeded by a factor of 3 the highest values reported in the literature.
The results showed, that Si and Ge superlattices could compete with the current materials used to commercialise thermoelectric modules. In addi- tion, these materials have the advantage of being compatible with MEMs and CMOS processing, so that they could be integrated as energy harvesters to create complete autonomous sensors.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Thermoelectric, Superlattices, Silicon and Germanium heterostructures, thermal and electrical characterization, micro/nano fabrication
• Subjects: Q Science > Q Science (General); Q Science > QC Physics; T Technology > TK Electrical engineering. Electronics Nuclear engineering
• Colleges/Schools: College of Science and Engineering > School of Engineering > Electronics and Nanoscale Engineering
• Supervisor's Name: Paul, Prof. Douglas
• Date of Award: 2014
• Depositing User: Miss Lourdes Ferre Llin
• Unique ID: glathesis:2014-4861
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 28 Mar 2014 09:32
• Last Modified: 28 Mar 2014 09:37
• URI: https://theses.gla.ac.uk/id/eprint/4861