Ultrafast spontaneous emission: Exciton radiative decay vs phonon scattering and disorder

Abstract

A theory of the exciton spontaneous emission from a semiconductor slab with strong exciton–photon interaction is developed. The limit of the radiative decay rate Γ large compared to the exciton–phonon scattering rate γ is studied for the first time. It is shown that simultaneous account for the structural disorder and exciton–acoustic phonon scattering results in a two-exponential photoluminescence decay under off-resonant pulse excitation. In a well-organized structure (weak disorder), the fast component determined by Γ can lead to ultrafast photoluminescence decay with the lifetime of tens of fs. In a strongly disordered structure the decay turns out to be one-exponential and independent of Γ, in accordance with recent experimental results.