Local disorder and optical properties in V-shaped quantum wires: Toward one-dimensional exciton systems (original) (raw)

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.

Near-field optical spectroscopy of localized and delocalized excitons in a single GaAs quantum wire

Physical Review B, 2001

Excitons in a GaAs quantum wire are studied in high-resolution photoluminescence experiments performed at a temperature of about 10 K with a spatial resolution of 150 nm, and a spectral resolution of 100 eV. We report an observation of quasi-one-dimensional excitons which are delocalized over a length of up to several microns along the quantum wire. Such excitons give rise to a 10-meV broad luminescence band, representing a superposition of transitions between different delocalized states. In addition, we find a set of sharp luminescence peaks from excitons localized on a sub-150-nm length scale. Theoretical calculations of exciton states in a disordered quasi-one-dimensional potential reproduce the experimental results.

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.

Disorder Effects on Carrier Dynamics in a Single Quantum Wire

phys. stat. sol. (a), 2002

An overview is presented of the optical properties in single GaAlAs/GaAs quantum wires grown on a V-grooved GaAs substrate studied by high spatial resolution spectroscopy. In these structures there is evidence for strong localization effects hiding completely the expected one-dimensional character of the system. Exciton dynamics are governed essentially by the properties of a zerodimensional system, since the monolayer fluctuations of the wire thickness create local potential minima that naturally form quantum boxes along the free axis of the wire. A systematic study of the exciton relaxation processes and radiative recombination as well as the fine structure of exciton states is presented as a function of the size of the quantum boxes.

Exciton relaxation and level repulsion in GaAs/Al_ {x} Ga_ {1-x} As quantum wires

2004

A common topic in the growth of semiconductor nanostructures, nowadays, concerns the quality of the interfaces. In general, quantum well QW and quantum wire QWR interfaces, although of very high quality, are rough at the atomic scale and just in few cases interfaces of exceptional quality extend over mesoscopic distances.

Exciton relaxation and level repulsion in quantum wires

physica status solidi (c), 2003

PACS 63.20. Ls, 73.20.Àr, 78.55.Cr, 78.67.Lt Luminescence spectra of V-groove GaAs/AlGaAs quantum wires are investigated at different temperatures by spatially resolved photoluminescence spectroscopy using a low temperature scanning near-field optical microscope (SNOM). Raising the sample temperature, the evolution of the photoluminescence spectra evidences that excitons are not completely relaxed in the deepest minima of the disordered potential. Simulations of exciton relaxation in a disordered 1D potential show that this behaviour is related to a reduction of the phonon scattering rates for the lowest lying states, which causes a bottleneck effect for exciton relaxation. These results suggest that the observed level repulsion effect in quantum wires is due to light emission from both fundamental and excited states localized in the same potential minima.

Existence of exciton crystals in quantum wires

Physical Review Letters, 1993

An exciton crystal (EC) is predicted in a quasi-one-dimensional (1D) semiconductor quantum wire for the densities (1 ( r, ( 5. 5) due to the repulsive interaction between singlet excitons (x s).