Evidence for Exciton Localization in V-Shaped Quantum Wires (original) (raw)
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Optical imaging spectroscopy of V-groove quantum wires: from localized to delocalized excitons
Physica E: Low-dimensional Systems and Nanostructures, 2003
The exciton localization and delocalization is studied in GaAs/GaAlAs V-shaped quantum wires (QWRs) by microscopy and spectroscopy. Scanning optical imaging of di erent 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 m, and form a continuum of 1D states in each of them. 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 built-in piezo-electric ÿeld in the structure.
Excitonic Effects in Quantum Wires
physica status solidi (a), 1997
We review the effects of Coulomb correlation on the linear and non-linear optical properties of semiconductor quantum wires, with emphasis on recent results for the bound excitonic states. Our theoretical approach is based on generalized semiconductor Bloch equations, and allows full three-dimensional multisubband description of electron-hole correlation for arbitrary confinement profiles. In particular, we consider V-and T-shaped structures for which significant experimental advances were obtained recently. Above band gap, a very general result obtained by this approach is that electron-hole Coulomb correlation removes the inverse-square-root single-particle singularity in the optical spectra at band edge, in agreement with previous reports from purely one-dimensional models. Strong correlation effects on transitions in the continuum are found to persist also at high densities of photoexcited carriers.
Phys. Rev. B, 2003
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 µm, and form a continuum of 1D states in each of them, as evidenced by the √ 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.
Excitonic lasing in semiconductor quantum wires
Physical Review B, 2000
Direct experimental evidences for excitonic lasing is obtained in optically pumped V-groove quantum wire structures. We demonstrate that laser emission at a temperature of 10 K arises from a population inversion of localized excitons within the inhomogenously-broadened luminescence line. At the lasing threshold, we estimate a maximum exciton density of about 1.8 10 5 cm -1 .
Excitons in T-shaped quantum wires
Physical Review B, 2001
We calculate energies, oscillator strengths for radiative recombination, and two-particle wave functions for the ground state exciton and around 100 excited states in a T-shaped quantum wire. We include the single-particle potential and the Coulomb interaction between the electron and hole on an equal footing, and perform exact diagonalisation of the two-particle problem within a finite basis set. We calculate spectra for all of the experimentally studied cases of T-shaped wires including symmetric and asymmetric GaAs/AlxGa1−xAs and InyGa1−yAs/AlxGa1−xAs structures. We study in detail the shape of the wave functions to gain insight into the nature of the various states for selected symmetric and asymmetric wires in which laser emission has been experimentally observed. We also calculate the binding energy of the ground state exciton and the confinement energy of the 1D quantum-wire-exciton state with respect to the 2D quantum-well exciton for a wide range of structures, varying the well width and the Al molar fraction x. We find that the largest binding energy of any wire constructed to date is 16.5 meV. We also notice that in asymmetric structures, the confinement energy is enhanced with respect to the symmetric forms with comparable parameters but the binding energy of the exciton is then lower than in the symmetric structures. For GaAs/AlxGa1−xAs wires we obtain an upper limit for the binding energy of around 25 meV in a 10Å wide GaAs/AlAs structure which suggests that other materials must be explored in order to achieve room temperature applications. There are some indications that InyGa1−yAs/AlxGa1−xAs might be a good candidate.
Exciton Dynamics in thin wires
Journal of Luminescence, 1987
When are molecular wires thin enough to show one-dimensional exciton kinetics? What are the characteristics of one-dimensional kinetics? What applications are there? Cylindrical naphthalene wires (5 5000 nanometer radius) show a definite one-to three-dimensional transition (about 25 nm for triplet excitons at 4 K; 40 nm at 77 K). Nuclear channel pore membranes (polycarbonate) serve as templates and calibrators. Monte Carlo simulations on finite-width wires are consistent with the experiments. Vycor glass pores are effectively one-dimensional. A new experimental criterion is based on excitation pulse width. It gives both topological and stochastic information (i.e. dimensionality and hopping rate) Its applicahilit~to ultrathin wires and porous glass is demonstrated via simulations and experiments. The triplet exciton migration (multiple hopping) length is 50 100 molecules for all samples.
High spatial resolution spectroscopy of a single V-shaped quantum wire
Applied Physics Letters, 1997
We report on microscopic photoluminescence of a single V-shaped AlGaAs/GaAs quantum wire. The experiments are performed at low temperature by selectively exciting 1 m 2 of the sample. The main photoluminescence line is split into sharp peaks of width less than 0.5 meV and separated by a few meV. The energy position and the intensity of the peaks are characteristic of the scanned quantum wire. First microphotoluminescence results suggest that localization phenomena are predominant in the quantum wire. They are due to the formation of extended monolayer-step islands, larger than the exciton radius, as in the case of high-quality quantum wells. © 1997 American Institute of Physics. ͓S0003-6951͑97͒00343-4͔
Exciton Binding Energy in GaAs V-Shaped Quantum Wires
Physical Review Letters, 1994
We have determined the main parameters of the quasi-one-dimensional excitons confined in GaAs V-shaped quantum wires, namely exciton Bohr radius and binding energy, by two-photon absorption and magnetoluminescence experiments. The experimental results are in excellent agreement with our calculations, based on realistic wave functions for the actual wire geometry.
Excitons in coupled InAs∕InP self-assembled quantum wires
Physical Review B, 2007
Optical transitions in coupled InAs/InP self-assembled quantum wires are studied within the single-band effective mass approximation including effects due to strain. Both vertically and horizontally coupled quantum wires are investigated and the ground state, excited states and the photoluminescence peak energies are calculated. Where possible we compare with available photo-luminescence data from which it was possible to determine the height of the quantum wires. An anti-crossing of the energy of excited states is found for vertically coupled wires signaling a change of symmetry of the exciton wavefunction. This crossing is the signature of two different coupling regimes.