Bulusu, Anuradha Ph.D. in Interdisciplinary Materials Science, August 2007 Research Information
Ph.D. Dissertation Coupled Quantum  Scattering Modeling of Thermoelectric Performance of Nanostructured Materials Using the NonEquilibrium Green's Function Method
Ph.D. Advisor Greg Walker, Mechanical Engineering
Committee Members Leonard Feldman, Physics Deyu Li, Mechanical Engineering Ronald Schrimpf, Electrical Engineering Norman Tolk, Physics

Abstract. Thermoelectric effects in materials allow for energy conversion in devices through the Seebeck effect and the Peltier effect. Applications of thermoelectric include electronics cooling, power generators for remote telecommunication etc. The usefulness of thermoelectric materials is characterized by the dimensionless figure of merit ZT = S2σT/κ where S is the Seebeck coefficient, σ is the electrical conductivity and κ is the thermal conductivity. The Seebeck coefficient and electrical conductivity depend only on the electronic properties of the material while the thermal conductivity can be dominated by contributions from both the electronic component as well as lattice vibrations. The advent of quantum well nanofilm and nanowire structures that improve the value of ZT through reduced thermal conductivity shifted the focus towards understanding carrier transport behavior in nanostructures. In this regard, the two main phenomena that affect electron transport in nanostructures are 1) electron confinement and 2) electron scattering effects such as electronphonon scattering, electronimpurity scattering etc. Common models to predict thermoelectric performance in nanostructures are based on finding a solution to the Boltzmann transport equation using the relaxationtime approximation where quantum effects are captured using quantum corrections to the model. The objective of this research is to develop a coupled quantumscattering model to calculate thermoelectric transport coefficients in nanostructures through the nonequilibrium Green’s function (NEGF) formalism. We propose to use the NEGF method as a design tool to model thermoelectric structures with optimized values of doping, effective mass, substrate strain and superlattice geometry taking into consideration the effects of electron confinement and scattering to give the best value of ZT. This effort represents the first reported use of the nonequilibrium Green’s function method to predict thermoelectric performance. Selected Publications
Onedimensional thinfilm phonon transport with generation. Bulusu, A; Walker, DG, MICROELECTRONICS JOURNAL, 39, 950956 , (2008) Quantum modeling of thermoelectric properties of Si/Ge/Si superlattices. Bulusu, A; Walker, DG, IEEE TRANSACTIONS ON ELECTRON DEVICES, 55, 423429 , (2008) Review of electronic transport models for thermoelectric materials. Bulusu, A; Walker, DG, SUPERLATTICES AND MICROSTRUCTURES, 44, , (2008) Modeling of thermoelectric properties of semiconductor thin films with quantum and scattering effects. Bulusu, A; Walker, DG, JOURNAL OF HEAT TRANSFERTRANSACTIONS OF THE ASME, 129, 492499 , (2007) Quantum modeling of thermoelectric performance of strained Si/Ge/Si superlattices using the nonequilibrium Green's function method. Bulusu, A; Walker, DG, JOURNAL OF APPLIED PHYSICS, 102, 073713 , (2007) 
