Summer 2010 Intern Project- John Haberstroh


John Haberstroh
CCS Physics
UC Santa Barbara

Mentor: Alex Sztein
Faculty Advisor: Shuji Nakamura
Department: Materials Science

Recent advances in Metal Organic Chemical Vapor Deposition have made GaN and it’s alloys a leading family of semiconductor materials. Despite this increased interest, however, the thermoelectric properties of this material system remain mostly unexplored, although a few basic studies hint that they may provide a good candidate high temperature (ZT = 1) thermoelectric material.. The goal of this project is to study in depth the properties of GaN and InGaN in the context of viewing it as a thermoelectric material.

The focus of this portion of the study is to model the thermoelectric properties of GaN based materials in order to understand their thermoelectric properties. The model used Boltzmann Transport Equation, solved with the scattering time approximation. These scattering times determine Seebeck coefficient, electrical conductivity, and thermal conductivities as functions of temperature and carrier density. These models agree well with the experimental data gathered in the study for temperatures greater than room temperature, as well as carrier densities near the optimized 1e19 cm-3. Future directions include expanding the model to novel microstructures like quantum dots and superlattices.

Other future directions include gathering data on GaN based materials at high temperatures. This is important because though results from this study have shown theoretical improvements in merit of GaN at high temperatures, the highest published temperature measurement is 450K . The high temperature data will be compared to the results of the theoretical model to provide a more comprehensive understanding of the thermoelectric properties of GaN based materials.

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