Thermal origin of light emission in non-resonant and resonant tunnel junctions

TL;DR

This study demonstrates that light emission in tunnel junctions originates from thermal radiation of a hot electronic subsystem, with experimental evidence from graphene-based electrodes confirming a Planck spectrum in non-resonant and combined thermal-resonant spectra in resonant setups.

Contribution

The paper introduces a novel experimental approach using fixed-distance epitaxial graphene electrodes to clearly distinguish thermal light emission mechanisms in tunnel junctions.

Findings

Light emission follows a Planck spectrum in non-resonant geometries.

Resonant environments add a resonant radiation component proportional to thermal emission.

Emission is driven by a hot electronic subsystem interacting with electromagnetic surroundings.

Abstract

Electron tunneling is associated with light emission. In order to elucidate its generating mechanism, we provide a novel experimental ansatz that employs fixed-distance epitaxial graphene as metallic electrodes. In contrast to previous experiments, this permits an unobscured light spread from the tunnel junction, enabling both a reliable calibration of the visible to infrared emission spectrum and a detailed analysis of the dependence of the parameters involved. In an open, non-resonant geometry, the emitted light is perfectly characterized by a Planck spectrum. In an electromagnetically resonant environment, resonant radiation is added to the thermal spectrum, both being strictly proportional in intensity. In full agreement with a simple heat conduction model, we provide evidence that in both cases the light emission stems from a hot electronic subsystem in interaction with its linear electromagnetic environment. These very clear results should resolve any ambiguity about the mechanism of light emission in nano contacts.