Thermoelectric power factor in thin-films and nanostructures.

摘要

Thermoelectric materials are used for power generation and local cooling applications. In this thesis, we study thermoelectric properties of different structures including impurity doped bulk semiconductors, thin films, single barrier heterostructures, metal/semiconductor superlattices and bulk structures with embedded spherical nano-particles. The thermoelectric properties of different samples were characterized experimentally. These measured properties were used to validate the developed theoretical modeling. Developed models include relaxation time approximation for linear transport, the Monte Carlo model for non-linear in-homogeneous transport, modified Boltzmann solver for superlattices and the coherent potential approximation to include randomness in the system. Electron-phonon exchange at interfaces is studied to identify the length scales of the Peltier cooling and heating. Nonlinear Peltier and Seebeck is investigated with the Monte-Carlo method. Enhanced cooling is observed due to nonlinearity at low temperatures and low doping concentrations. Nano-particle doped sample are promising if they contribute electrons to the conduction band but scatter them weakly. It is shown that more than 400% enhancement is achievable at low temperatures compared to the impurity doped samples. Nitride Metal/Semiconductor superlattices are very promising at high temperatures (more than 800K). It is shown that by engineering their band offset, they can have ZT values as high as 3.