Phonon-mediated quantum processes in semiconductors from first principles

Quantum processes among electrons, excitons, photons, and phonons lie at the heart of the operation of semiconducting devices for electronics, optoelectronics, and energy applications. Many of these processes are direct, such as the absorption and emission of light in direct-gap semiconductors, and can be treated with a high degree of accuracy using modern computational methods based first-order perturbation theory. In other cases, however, such as for optical transitions in indirect-gap materials, direct processes are forbidden by energy and momentum conservation, and the dominant indirect processes are enabled by the additional momentum provided by phonons. In this talk, I will present our work on the development and application of first-principles computational methods and codes for the predictive study of phonon-mediated quantum processes in semiconducting materials. I will discuss how phonons enable light absorption in indirect-gap semiconductors such as Si, BAs, and SiC, as well as how phonon-mediated transitions introduce optical loss in metals and doped semiconductors. I will also present our work on the phonon-mediated radiative recombination of excitons in indirect-gap semiconductors, and how these phonon-assisted processes in indirect-gap materials such as hexagonal BN can be as strong or even stronger than in direct-gap semiconductors. Last, I will also present our methodology for the study of non-radiative Auger-Meitner recombination in semiconductors, and how phonons are crucial to accurately quantify the non-radiative loss in silicon solar cells and in nitride optoelectronic devices. Our work sheds light on the intrinsic energy-conversion and loss mechanisms that are at work in modern semiconducting materials, and can propose avenues to alleviate them and improve the efficiency of devices.