Radiatively broadened thermal emitters

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.