Executive Summary : | In the history of TE materials, in the 1950s and 1960s, doped semiconductors were identified as best candidates, due to the flexibility to control their electronic band structure. This gave a very high figure of merit (zT) values close to unity. Bismuth, Antimony, lead, selenium, tellurium and their compounds are known to be best materials. They still remain the best choice for TE power generation devices as oxides and more earth-abundant materials like suffer from low zT. Materials such as intermetallic alloys, clatharates, chalcogenides, skutterudites etc. have been the primary choice for TE applications[11]. The TE zT of these materials is only improving each passing year as we go to next generation thermoelectrics with zT=2 and 3 in materials like PbSe, SnSe and GeTe Most of these materials show high zT due to unique attributes such as unharmonic lattice vibration[14] (low thermal conductivity), high band degeneracy (high seebeck coefficient and optimum carrier mobility. Nevertheless, no single material is reported so far has high zT in the entire temperature range of 300 to 700 K, let alone flat temperature independent zt. Either the thermoelectric Figure of Merit (FoM) is high near room temperature as in case of Bi2Te3, or near 500 K like Sb2Te3 or at high temperatures i.e.above 500K for GeTe and SnSe etc. In this project, our objective is to fabricate thermoelectric thin films having a superlattice structures of Bi2Te3, Sb2Te3 and GeTe with the aim that it will be having a high zt throughout the temperature range of 300 to 700K or more. Such that these thin films can be practically more efficient for cooling applications. The modulation of uniformity and coherency of the nanocomposite has pronounced effect on the TE properties. and hence, study of composition and microstructure forms integral part of the project. The thin films deposition is proposed by semiconductor fabrication process friendly method of Atomic layer deposition (ALD) which offers greater control over crystallinity, conformity and interface engineering. |