Thermal relaxation of electrons in semiconductors*

Using a novel first-principles framework, we study the timescales of energy transfer and thermalization of highly energetic "hot" electrons with an atomic lattice for semiconductors [1]. In particular, we compute phonon-specific temperatures and account for both phonon-phonon and electron-phonon interactions in our semiclassical description. For polar and nonpolar semiconductors, we show that the coupled phonon and electron dynamics departs qualitatively from the two-temperature (2T) physical picture over time scales ranging from 1 to 100 ps after excitation. We demonstrate that this disagreement stems from the breakdown of the hypothesis of thermal equilibrium within the lattice subsystem, and generalize the 2T model of Allen [2] to account for slow phonon thermalization as a limiting step of electron-phonon thermalization. We discuss how our model can be used to extract more information on the electron-phonon interactions from time-resolved spectroscopy experiments.
[1] Sadasivam, Chan, Darancet PRL 119, 136602 (2017)
[2] Allen, Phys. Rev. Lett. 59, 1460 (1987)