When 12:00 PM - 2:00 PM Aug 05, 2015
Where 1670 Beyster Building
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First-Principles Calculations of Optoelectronic and Transport Properties of Materials for Energy Applications


Dylan Bayerl
Thesis Defense

Emmanuel Kioupakis, advisor

 

Modern semiconductor technology and nanoengineering techniques enable rapid development of new materials for energy applications such as photovoltaics, solid- state lighting, and thermoelectric devices. Yet as materials engineering capabil- ities become increasingly refined, the space of controllable properties becomes increasingly large and complex. Selecting the most promising materials and pa- rameters to focus on represents a significant challenge.

 

We approach this challenge by applying state-of-the-art predictive first-principles calculation methods to guide research and development of materials for energy applications. This work describes our first-principles investigations of nanos- tructured group-III-nitrides for solid-state lighting applications and bulk titanium dioxides for thermoelectric applications.

 

We demonstrate several remarkable properties of nanostructured group-III- nitrides, including visible light emission from highly quantum-confined InN nanowires and tunable ultraviolet light emission with enhanced radiative recombi- nation efficiency in ultra-thin GaN-AlN quantum wells. These findings highlight the capability of quantum-confined group-III-nitrides to improve the efficiency and utility of visible and ultraviolet solid-state light emitters. Additionally, we calculate the n-type thermoelectric transport properties of nat- urally occurring polymorphs of TiO2 and predict optimal temperatures and free- carrier concentrations for thermoelectric energy conversion. We also predict the- oretical limits on the figure of merit ZT and demonstrate that TiO2 can achieve thermoelectric energy conversion efficiency comparable to that of commercialized thermoelectrics.