Spontaneous emission, elastic scattering and localization of exciton‐polaritons in disordered quantum wells

Abstract

PACS 71.35.Cc, 78.67.Pt Steady-state resonant effects due to multiple scattering of exciton-polaritons are studied for quantum wells in disordered semiconductor multilayers. Single quantum wells with laterally fluctuating width and random arrays of quantum wells are considered as the basic objects with intra-and inter-well disorder. Discussed are the following issues: a model of fluctuating quasi-2D exciton polarization, steady-state resonant Rayleigh scattering and resonant localization of exciton-polaritons. 1 Introduction Coherent re-emission of photons from low-dimensional excitonic states is known to cause exciton-polaritonic energy transfer through quantum-size structures. Imperfections of real heterostructures induce resonant elastic (Rayleigh) scattering of light mediated by exciton-polaritons. Coherent scattering, rather than incoherent luminescence, dominates in the emission from exciton states at low densities of optical excitation. Study of polaritonic versus excitonic character of resonant Rayleigh scattering (RRS) from disordered quantum wells (QW) is a complex problem, with spectral, temporal and spatial (angular) aspects being essential. The first two manifests directly in time-resolved emission from disordered QWs dealt with in most works, e.g. [1][2][3], where the concept of random potential affecting the motion of exciton center-of-mass in QW plane is exploited. The fitted correlation lengths of the potential range from a few nanometers to a few thousand nanometers [1-3], the differences being unexplained. From the viewpoint of scattering (diffraction) theory [4], the extreme of the cited values serve as a sign that the probed static disorder hardly could be optimum for electromagnetic (polaritonic) RRS. This is confirmed by the observation [5] that the angle dependences of steady-state RRS from semiconductor rough surfaces is the most informative for roughness whose correlation length is comparable with the wavelength of light. One can soundly argue that interface profiles seen by a probing electromagnetic wave and by an exciton are different rather than identical. Actually, atomic-force microscopy of semiconductor surface reveals two correlation lengths belonging to short-scale (≈ 40 nm) and long-scale (≈ 300 nm) surface shape fluctuations, and it is only the long-scale disorder that manifests in RRS from the surface in excitonic spectral range [6].This work is focused on the steady-state RRS through exciton-polariton states. Discussed are the polaritonic multiple-scattering effects in semiconductor quantum-well structures with both intra-well and inter-well disorder. Spectral and especially angular features of RRS from single quantum wells are studied for a developed model of fluctuating exciton polarization, and one-dimensional localization of polaritons is analyzed for disordered arrays of QWs.