Exciton-phonon coupling effects on the optical properties of semiconductors: an ab-initio density functional theory approach

Temperature effects play an important role on the performance of optoelectronic devices since they induce significant changes in the electronic and optical properties of different materials. Although there is a significant understanding of these phenomena on conventional semiconductors such as silicon and III-V alloys, the role played by the electron-phonon interaction on the photo excited states of novel synthesized layered-materials such as black phosphorus (BP) and its allotropes are in its early stage. Therefore, theoretical studies concerning the exciton-phonon coupling are needed in order to elucidate its role on the optical properties, and consequently, help in the design of novel optoelectronic devices based on these interesting materials. In that sense, this project will use ab-initio density functional theory simulations combined with the many-body perturbation theory that includes a temperature dependent self-energy term that accounts for the electron-phonon interaction in the system. Thus, we will study the exciton-phonon coupling effects on the optical spectrum of w-GaN as well as layered-materials such as BP and its allotropes. By studying w-GaN we will be able to validate the methodology with available experimental measurements. For the case of BP, we will focus on the optical response for different incident light-polarization and number of layers as the anisotropic structure of BP leads to interesting optical properties. In addition, based on Fermi's golden rule, we will explore the role of temperature over the exciton lifetimes as well as exciton extension radius, oscillator strength intensity, and optical transitions which are crucial processes in determining the performance of optoelectronic devices. Finally we will propose a prototypical photovoltaic device based on BP heterostructures and study its performance as a function of temperature. (AU)