Ab initio study of hot electrons in GaAs

Abstract

Hot carrier dynamics critically impacts the performance of electronic, optoelectronic, photovoltaic, and plasmonic devices. Hot carriers lose energy over nanometer lengths and picosecond timescales and thus are challenging to study experimentally, whereas calculations of hot carrier dynamics are cumbersome and dominated by empirical approaches. In this work, we present ab initio calculations of hot electrons in gallium arsenide (GaAs) using density functional theory and many-body perturbation theory. Our computed electron–phonon relaxation times at the onset of the Γ, L, and X valleys are in excellent agreement with ultrafast optical experiments and show that the ultrafast (tens of femtoseconds) hot electron decay times observed experimentally arise from electron–phonon scattering. This result is an important advance to resolve a controversy on hot electron cooling in GaAs. We further find that, contrary to common notions, all optical and acoustic modes contribute substantially to electron–phonon scattering, with a dominant contribution from transverse acoustic modes. This work provides definitive microscopic insight into hot electrons in GaAs and enables accurate ab initio computation of hot carriers in advanced materials. Significance How does an excited electron lose its energy? This problem is central in fields ranging from condensed matter physics to electrical engineering and chemistry. The cooling of hot electrons in gallium arsenide (GaAs) is the critical process underlying the operation of exciting electronic and optoelectronic devices, but the nature of this cooling is controversial. Here, we present calculations showing that hot electrons in GaAs lose energy chiefly by emitting lattice vibrations. We find a dominant role of acoustic vibrations, challenging the common notion that optical vibrations dominate excited electron energy loss. Our computational approach shines light on microscopic processes that are hard to capture with both experiments and semi-empirical calculations and opens new avenues to compute excited electron dynamics.