When heat goes astray -- non-local heating in a semiconductor

TL;DR

This paper demonstrates that in semiconductor membranes, heat distribution can be non-local and exceed local laser heating due to ballistic phonon transport, challenging traditional Fourier law assumptions.

Contribution

It reveals non-local heat transfer phenomena in semiconductors on micrometer scales, driven by ballistic phonons, contradicting classical heat conduction models.

Findings

Non-local heating can surpass local laser heating in semiconductor membranes.

Ballistic phonon transport occurs at temperatures well above cryogenic levels.

Heat locality assumptions break down on micrometer length scales.

Abstract

Heating of semiconductor devices limits their performance and lifetime, which must be addressed by thermal management starting at the heat source. It is a common assumption that the heat source and the resulting heat spot locally coincide, if their size exceeds the mean free paths of the main heat carriers, the phonons. We show that this paradigm of heat locality breaks down on length scales spanning several micrometers. As a consequence, non-local heating occurs in contradiction to Fourier's law. Therefore, we heat laterally structured semiconductor membranes that feature a rising number of interfaces with a well-focussed laser and map-out lattice temperatures by Raman thermometry. Remarkably, the non-local heating can exceed the laser-induced local heating, which we attribute to ballistic phonon transport far above cryogenic temperatures.