Abstract

THERMOELECTRIC GENERATORS are devices for direct conversion of heat into electricity. Their outstanding reliability due to the lack of moving parts makes them attractive candidates for a series of applications. However, today's thermoelectric devices are limited by their low efficiency and high costs. Thus, their operation is restricted to highly specialized niches. Optimization of thermoelectric devices to given thermal and geometrical constraints depends on a physics-based simulation framework. This work focuses on the extension and application of semiconductor device simulation, which is a well established tool in mainstream microelectronics to thermoelectrics.

In the theoretical part, proper transport description for thermoelectric devices is developed. Models based on different approximations of the scattering operator within Boltzmann's equation are systematically derived by the method of moments and compared to a phenomenological approach based on the principles of irreversible thermodynamics. Models for the Seebeck coefficient, which play a major role in thermoelectric devices are discussed and compared to measurement data.

A material related part highlights important properties of thermoelectric materials as well as mechanisms for possible optimization. After an overview of the most important thermoelectric materials and their attributes, the focus is put on lead telluride, which serves as a thermoelectric material in the intermediate temperature range. A detailed discussion on the physical modeling of several simulation-relevant material properties is carried out.

The practical part incorporates case studies of both conventional thermoelectric devices as well as a novel structure containing a large scale pn-junction. Simulation results for both silicon and lead telluride structures are compared to measurement data, whereby excellent agreement is achieved. In a detailed simulation study, the influences of several design parameters like geometry, material composition, and doping profiles on the device performance of thermoelectric generators are assessed. Furthermore, the device behavior is discussed within non-ideal thermal environments. The novel structure incorporating a large scale pn-junction turns out to be highly adaptable to given environmental conditions.

M. Wagner: Simulation of Thermoelectric Devices