The morphology of the InAs/GaAs(001) system has been imaged by atomic force microscopy (AFM) at different stages of the epitaxial growth from the initial formation of a pseudomorphic two-dimensional (2D) interace up to the self-aggregation of InAs quantum dots (QDs). The substrate texture and the dependence of the cation diffusion on the elastic strain field fully control the lateral ordering of the nanoparticles in the self assembling process and determine the final morphology of multistacked InAs QD arrays. (C) 2002 American Institute of Physics

Exciton-polariton propagation in a quantum well, under centre-of-mass quantization, is computed by a variational self-consistent microscopic theory. The Wannier exciton envelope functions basis set is given by the simple analytical model of ref.[1], based on pure states of the centre-of-mass wave vector, free from fitting parameters and "ad hoc" (the so called additional boundary conditionsABCs) assumptions. In the present paper, the former analytical model is implemented in order to reproduce the centre-of-mass quantization in a large range of quantum well thicknesses (5aB ≤ L ≤ ∞). The role of the dynamical transition layer at the well/barrier interfaces is discussed at variance of the classical Pekar's dead-layer and ABCs. The Wannier exciton eigenstates are computed, and compared with various theoretical models with different degrees of accuracy. Excitonpolariton transmission spectra in large quantum wells (L ≫ aB) are computed and compared with experimental results of Schneider et al.2 in high quality GaAs samples. The sound agreement between theory and experiment allows to unambiguously assign the exciton-polariton dips of the transmission spectrum to the pure states of the Wannier exciton center-of-mass quantization.

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The exciton–polariton propagation in resonant hybrid periodic stacks of isotropic/anisotropic layers, with misaligned in-plane anisotropy and Bragg photon frequency in resonance with Wannier exciton of 2D quantum wells is studied by self-consistent theory and in the effective mass approximation. The optical tailoring of this new class of resonant Bragg reflectors, where the structural periodicity of a multi-layer drives the in-plane optical -axis orientation, is computed for symmetric and asymmetric elementary cells by conserving strong radiation–matter coupling and photonic band-gaps. The optical response computation, on a finite cluster of N-asymmetric elementary cells, shows anomalous exciton–polariton propagation and absorbance properties strongly dependent on the incident wave polarizations. Finally, the behaviour of the so-called intermediate dispersion curves, close to the unperturbed exciton resonance, and located between upper and lower branches of the first band gap, is studied as a function of the in-plane -axis orientation. This latter optical property is promising for storing exciton–polariton impulses in this kind of Bragg reflector.

The presence of a ternary alloy as well material in InxGa1−xAs/GaAs(001) strained quantum wells introduces a disorder mechanism by which the optical selection rules for symmetric wells may be relaxed and forbidden transitions usually appear in optical spectra. Strain and alloy disorder are studied as a function of well thickness and indium concentration in noninteracting double quantum wells of InxGa1−xAs/GaAs(001). Optical spectra are compared with an accurate Wannier exciton model. The agreement between theory and experiments points out that the optical selection rule for symmetric wells is restored in “high quality” and rather thin quantum wells. Finally, the presence of forbidden transitions in optical spectra is used as a fingerprint of nonhomogeneous indium concentration in thick quantum wells. This property is promising in order to study indium composition for well thicknesses in the range of quasi-two-dimensional behavior of the Wannier exciton.