High-field charge transport in semiconductors is of fundamental interest and practical importance. While the ab initio treatment of low-field transport is well developed, the treatment of high-field transport is much less so, particularly for multiphonon processes that are reported to be relevant in GaAs. Here, we report a calculation of the high-field transport properties and current power spectral density (PSD) of hot electrons in GaAs from first principles including on-shell two-phonon (2ph) scattering. The on-shell 2ph scattering rates are found to qualitatively alter the high-field distribution function by increasing both the momentum and energy relaxation rates as well as contributing markedly to intervalley scattering. This finding reconciles a long-standing discrepancy regarding the strength of intervalley scattering in GaAs as inferred from transport and optical studies. The characteristic nonmonotonic trend of PSD with electric field is not predicted at this level of theory. Our work shows how ab initio calculations of high-field transport and noise may be used as a stringent test of the electron-phonon interaction in semiconductors.

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• Electrical conductivity
• Electron relaxation
• Electron-phonon coupling
• First-principles calculations
• Noise
• Transport phenomena
• Boltzmann theory