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.hot carriers | semiconductors | GaAs | ultrafast | electron-phonon scattering H ot carriers (HCs) generated by the absorption of light or injection at a contact are commonly found in many advanced technologies (1-9). In electronics, the operation of high-speed devices is controlled by HC dynamics, and HC injection is a key degradation mechanism in transistors (10, 11). In solar cells and plasmonics, recent work has focused on extracting the kinetic energy of HCs before cooling (7, 9), a process defined here as the energy loss of HCs, ultimately leading to thermal equilibrium with phonons. HC dynamics is also crucial to interpret time-resolved spectroscopy experiments used to study excited states in condensed matter (12). This situation has sparked a renewed interest in HCs in a broad range of materials of technological relevance.Experimental characterization of HCs is challenging because of the subpicosecond timescale associated with the electron-phonon (e-ph) and electron-electron (e-e) scattering processes regulating HC dynamics. For example, HCs can be studied using ultrafast spectroscopy, but microscopic interpretation of time-resolved spectra requires accurate theoretical models. However, modeling of HCs thus far has been dominated by empirical approaches, which do not provide atomistic details and use ad hoc parameters to fit experiments (13,14). Notwithstanding the pioneering role of these early studies, the availability of accurate ab initio computational methods based on density functional theory (DFT) (15) and many-body perturbation theory (16) enables studies of HCs with superior accuracy, broad applicability, and no need for fitting parameters.Hot electrons in gallium arsenide (GaAs) are of particular interest because of the high electron mobility and multivalley character of the c...

First-principles calculations of thermal, electrical, and thermoelectric transport properties of semiconductors

“…Along this path, we think some of the challenges include the consideration of the spin-orbit coupling for heavy elements and alloy (and doping) effects on the electrical transport. Since the band structure greatly affects the scattering rate profile as we have seen in GaAs [122], more advanced first-principles method such as GW calculation (a method to more accurately describe the electron-electron interaction with G stands for Green's function and W stands for the screened Coulomb interaction) to take into account the electron many-body effects on the band structure will be necessary for a better description of the electronic properties.…”

“…9c), and a GW calculation (including electron many-body effect) was used to accurately describe the band structure [122]. [38].…”

“…Copyright (2015) American Physical Society; Doped Si results reprinted with permission from Qiu et al [37]. Copyright (2015) Institute of Physics; GaAs results reprinted with permission from Bernardi et al [122]. Copyright (2015) United States National Academy of Sciences)…”

“…For a finite phonon wave vector, DFPT exactly solves the eigen-equation and therefore automatically includes such long-range effect. This merit of DFPT is also used in the study of hot electron relaxations in GaAs [122].…”

Temperature tuning from direct to inverted bistable electroluminescence in resonant tunneling diodes

“…1(c)), impact ionization processes in the GaInNAs region, and additional parasitic voltage drops. For polar GaAs and the high energy electrons involved in the ionization process, the energy loss is mainly attributed to LO-phonon generation (see Reference 27 for a discussion about optical and acoustic phonon contributions) with an energy loss of 36 meV per phonon emission 28,29 . Fig.…”