Hot Electron Dynamics Modulated by Nonequilibrium Phonon Excitations

With advances in device miniaturization, understanding and manipulating nanoscale hot electron dynamics in semiconductors is recognized as an essential factor for improving performance and energy efficiency in optoelectronics and logic devices in the post-Moore era. This work demonstrates an effective strategy to modulate hot electron dynamics through nonequilibrium phonon excitations, utilizing first-principles-based mode-resolved electron-phonon coupled Boltzmann transport equation calculations. Two different phonon-mediated pathways for perturbing hot electron relaxation dynamics in doped semiconductors are illustrated, i.e., high-frequency optical phonons (e.g., longitudinal optical phonons in GaN) and low-frequency acoustic phonons, both of which exhibit strong coupling with electrons. While exciting high-frequency optical phonons to significant nonequilibrium states can quickly reheat and elevate electron temperatures, their rapid energy decay to other phonons fails to continuously slow down the subsequent hot electron relaxation. In contrast, the weak coupling of low-frequency acoustic phonons with other phonons facilitates the excitation of long-lived phonon nonequilibrium, which effectively prolongs the hot electron relaxation process from a few to tens of picoseconds for GaN, AlN, and Si. These findings reveal a general mechanism to modulate hot electron dynamics in device semiconductors, offering promising approaches to enhance the energy efficiency of advanced nanoscale devices.