Anisotropic Hot-Electron Kinetics Revealed by Terahertz Fluctuation

Abstract

In modern electronics, understanding hot-electron kinetics along with related lattice heating on nanoscales is prerequisite for realizing functional devices with the highest energy efficiency. Conventional nanothermometry techniques using either (contact-type) thermal sensing or (noncontact-type) optical excitation schemes are, however, fundamentally insensitive and typically intrusive to the embedded hot electrons. Here we image nanoscopic hot-electron distributions by passively detecting their intrinsic terahertz fluctuations. Through direct comparison with lattice heat, we demonstrate that, in GaAs current-carrying nanodevices, the effective temperature of the hot electrons is not only quantitatively much higher than that of the hosting lattice (Te ≫ TL) but also exhibits discernibly different spatial profiles, deviating from common expectation of mutual imprints between Te and TL in the solid-state environment. Te-profiles seen from the terahertz fluctuation mapping show microscopic hot-electron kinetic behaviors; in particular, crystalline anisotropy in hot electron kinetics has been found: Neighboring electron hotspots expand toward crystallographically favored orientations and eventually merge to form a self-organized directional hot-electron domain. This work demonstrates the powerfulness of a passive terahertz nanoimaging technique for probing nanoscale hot-electron kinetics in operative nanodevices that will help realization of efficient heat management in the future solid-state electronics.