open access

https://hdl.handle.net/2115/45958

Concept and Applications of Carrier Pocket Engineering to Design Useful Thermoelectric Materials Using Superlattice Structures

英語

2000-04

411

In this thesis, a general optimization approach to maximize the values of the thermoelectric figure of merit Z3DT is proposed using semiconducting superlattice systems.This optimization process, denoted by the "Carrier Pocket Engineering concept" in the text, takes the following four stages of actual investigation: (I) theoretical predictions for the materials combinations to be used and for the detailed structure of the superlattices in order to achieve the maximum value of Z3DT for the whole superlattice, using the simplest possible models; (II) experimental proof-of-principle study of the theoretical predictions made in (I) and give feedback to the theoretical concept and its explicit implementation; (III) improvement of the theoretical models to understand the experimental results obtained in (II) and to make improved theoretical predictions; and (IV) application of the knowledge acquired for the mechanisms responsible for enhancing Z3DT during the investigation of one materials system, to another materials system that may provide even larger values of Z3DT after incorporating the newly acquired knowledge for enhancing Z3DT. To demonstrate the above optimization process, a series of theoretical and experimental investigations were carried out using the following materials systems : (1) (Ill) oriented PbTe/Pb1_xEuxTe multiple-quantum-well superlattices to clarify the detailed mechanisms responsible for the previously observed enhancement in the thermoelectric power S in this system; (2) GaAs/AIAs short-period superlattices to propose the new concept of Carrier Pocket Engineering, where unconventional X- and L-point valleys, that do not contribute to the thermoelectric transport in the bulk form, can be made to contribute to the thermoelectric transport in the superlattice form, enhancing the values of Z3DT significantly relative to those for the corresponding bulk materials; (3) Si/Ge short-period superlattices to propose a yet new concept of lattice strain engineering to further increase the values of Z3DT in this superlattice system, and to provide an experimental proof-of-principle study of the Carrier Pocket Engineering concept using this materials system. Besides the above main stream of this thesis, the properties of (111) oriented PbTe/ Te and PbSe0.98Te0.02/PbTe "quantum-dot" superlattices, (001) oriented shortperiod superlattices of PbTe/Pb1_xEuxTe, and (111) oriented Bi/Pb1_xEuxTe superlattices are also discussed as possible candidates for the future high ZT materials.

2000-04

博士(工学)

博士論文

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