Fluctuations in the optical spectra of disordered microstructures due to quantum-interference effects

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Abstract
We describe a novel quantum-interference phenomenon that gives rise to fluctuations in the optical spectra of disordered microstructures when the inelastic scattering time in the structures exceeds the radiative recombination lifetime. The origin of this phenomenon lies in the fact that an electron or hole, forming an optical dipole, does not lose its phase memory in the absence of inelastic scattering. Consequently, when the dominant relaxation process for the optical dipole moment is elastic impurity scattering, the optical spectra of disordered samples depend sensitively on the phase relationships between the various electron (hole) states in the system due to quantum interference. Since these phase relationships themselves depend on the exact locations of the impurities (scattering centers) within the structure, the optical spectra will also depend on the precise details of the impurity ‘‘configuration’’ inside the structure. In addition, if the phase relationships are altered with an external field which perturbs the states, the optical spectrum will exhibit sample-specific fluctuations. In many ways, this phenomenon is an optical analog of ‘‘universal conductance fluctuations’’ and indeed has the same physical origin. An important consequence of this phenomenon is that in a superlattice structure, each quantum well will have a slightly different optical spectrum if they merely have different impurity configurations but are otherwise identical. Consequently, this phenomenon will induce a unique type of inhomogeneous broadening in such a structure. This inhomogeneous broadening can be quite large and at low enough temperatures can even be the dominant cause of linewidth broadening.