Fano Resonances In The Excitation Spectra Of Semiconductor Quantum Wells

Fano resonances are observed in the photoluminescence excitation spectra of GaAs-AlAs quantum wells. They originate from the Coulomb interaction that couples a discrete state and a continuum of excitonic states belonging to different pairs of conduction and valence subbands. This interpretation is supported by our calculations and by the behavior of the excitonic line shape in the presence of a magnetic field applied perpendicular to the layers. © 1994 The American Physical Society.4985757576

Local disorder and optical properties in V-shaped quantum wires : towards one-dimensional exciton systems

The exciton localization is studied in GaAs/GaAlAs V-shaped quantum wires (QWRs) by high spatial resolution spectroscopy. Scanning optical imaging of different generations of samples shows that the localization length has been enhanced as the growth techniques were improved. In the best samples, excitons are delocalized in islands of length of the order of 1 micron, and form a continuum of 1D states in each of them, as evidenced by the sqrt(T) dependence of the radiative lifetime. On the opposite, in the previous generation of QWRs, the localization length is typically 50 nm and the QWR behaves as a collection of quantum boxes. These localization properties are compared to structural properties and related to the progresses of the growth techniques. The presence of residual disorder is evidenced in the best samples and explained by the separation of electrons and holes due to the large in-built piezo-electric field present in the structure.Comment: 8 figure

Donor states in modulation-doped Si/SiGe heterostructures

We present a unified approach for calculating the properties of shallow donors inside or outside heterostructure quantum wells. The method allows us to obtain not only the binding energies of all localized states of any symmetry, but also the energy width of the resonant states which may appear when a localized state becomes degenerate with the continuous quantum well subbands. The approach is non-variational, and we are therefore also able to evaluate the wave functions. This is used to calculate the optical absorption spectrum, which is strongly non-isotropic due to the selection rules. The results obtained from calculations for Si/Si$_{1-x}$Ge$_x$ quantum wells allow us to present the general behavior of the impurity states, as the donor position is varied from the center of the well to deep inside the barrier. The influence on the donor ground state from both the central-cell effect and the strain arising from the lattice mismatch is carefully considered.Comment: 17 pages, 10 figure

Quantum Dot Exciton Dynamics Probed by Photon-Correlation Spectroscopy

The dynamics of charging and recombination of photoexcited, site-controlled semiconductor quantum dots (QDs) are investigated using microphotoluminescence (PL) and photon-correlation spectroscopy combined with rate equation modeling. Several species of neutral and charged exciton complexes are identified in the PL spectra and their dynamics are evaluated by analyzing the temporal profiles of the second-order auto- and cross-correlation functions. The results provide insight into exciton dynamics relevant for designing QD structures for applications in quantum information processing and quantum communication systems

Correlation between optical properties and interfaces morphology of GaAs/AlGaAs quantum wells

We investigate the embedded interfaces of GaAs/AlGaAs quantum wells grown by metal organic vapor phase epitaxy on slightly (< 1 degrees)-misoriented (001) substrates using selective etching and atomic force microscopy. Depending on the substrate misorientation, we observe different growth modes at the embedded interfaces, which are directly correlated to the photoluminescence linewidth. We show that the narrowest linewidth is obtained on 0.2 degrees-off (001) substrates for which the heterointerfaces consist of atomically smooth narrow terraces. We investigate the embedded interfaces of GaAs/AlGaAs quantum wells grown by metal organic vapor phase epitaxy on slightly (< 1 degrees)- misoriented (001) substrates using selective etching and atomic force microscopy. Depending on the substrate misorientation, we observe different growth modes at the embedded interfaces, which are directly correlated to the photoluminescence linewidth. We show that the narrowest linewidth is obtained on 0.2 degrees-off (001) substrates for which the heterointerfaces consist of atomically smooth narrow terraces. (c) 2006 American Institute of Physics