Radiatively broadened thermal emitters

TL;DR

This paper investigates how radiative and non-radiative processes influence the incandescence spectrum of a heavily doped quantum well with collective electronic excitations, revealing angle-dependent emission characteristics and conditions for perfect emissivity.

Contribution

It introduces a quantum Langevin model for radiatively broadened emitters, showing angle-dependent emission spectra and conditions for unity emissivity in a solid-state system.

Findings

Emission spectrum shape depends on radiative/non-radiative rate ratio.

Emissivity can reach unity at specific angles.

Angular emission pattern differs from a simple dipole.

Abstract

We study the incandescence of a semiconductor system characterized by a radiatively broadened material excitation. We show that the shape of the emission spectrum and the peak emissivity value are determined by the ratio between radiative and non-radiative relaxation rates of the material mode. Our system is a heavily doped quantum well, exhibiting a collective bright electronic excitation in the mid-infrared. The spontaneous emission rate of this collective mode strongly depends on the emission direction and, uncommonly for a solid-state system, can dominate non-radiative scattering processes. Consequently the incandescence spectrum undergoes strong modifications when the detection angle is varied. Incandescence is modelled solving quantum Langevin equations, including a microscopic description of the collective excitations, decaying into electronic and photonic baths. We demonstrate that the emissivity reaches unity value for a well-defined direction and presents an angular radiative pattern which is very different from that of an oscillating dipole.