Thermoelectric Properties of Self-Assembled Nanocristals in Semiconductor Matrix: Experiment and Theory

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Goal of this project is the continuation of the experimental and theoretical investigation of the thermoelectric properties of multilayers of defect-free nanocrystals (quantum dots, QDs) made of SiGe (InGaAs) in Si (GaAs) matrix. The investigations will be extended to quantum posts (QPs), i.e. short nanowires coherently embedded in SiGe (InGaAs). During the current funding period we have shown experimentally that it is possible to precisely control the thermal conductivity of Ge/Si multilayers down to values as low as 1 W/m.K. In addition, we have theoretically predicted that by proper engineering of the properties of QD multilayers, increased values of power factor can be expected. However, experimental measurements of cross-plane thermopower and electric conductivity are still scarce. We will therefore study cross-plane thermoelectric properties of QDs and QPs by varying relevant structural parameters, such as interlayer spacing, and doping level. The results will be compared to calculations using a realistic description of the electronic structure obtained from atomistic modelling and a treatment of thermoelectric transport beyond the constant-relaxation-rate approximation. Moreover, theoretical methods for treating combined non-equilibrium effects in both the electron and phonon system will be developed. The comparison between the two material systems and between QDs and QPs is expected to provide a significant advance on the understanding of the thermoelectric properties of nanostructured semiconductors.