Localization-Dependent Photoluminescence Spectrum of Biexcitons in Semiconductor Quantum Wires (original) (raw)

One-dimensional biexcitons in a single quantum wire

2002

We report the direct observation of one-dimensional (1D) excitonic molecules (biexcitons) in high quality disorder free semiconductor quantum wires. By means of spatially resolved near-field photoluminescence spectroscopy, we detected delocalized 1D excitons through the spatial extension of their homogeneous emission. 1D biexciton transitions are evidenced by their correlation to the 1D excitons as well as their power dependence.

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

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.

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.

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.

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.

Exciton localization and migration in individual CdSe quantum wires at low temperatures

2009

Low-temperature ͑Ͻ40 K͒ photoluminescence ͑PL͒ spectra of individual CdSe nanocrystal quantum wires exhibit narrow ͑Ͻ5 meV͒ isolated peaks spanning a range Յ50 meV. We attribute these features to emission of excitons localized in shallow ͑a few meV deep͒ tight potential minima superimposed on longer-scale and larger-amplitude variations of the potential energy. Spectrally resolved PL dynamics reveal decreasing excitondecay rates with decreasing emission energy. These observations are consistent with exciton relaxation within a manifold of localization sites characterized by an exponential density of states.

Probing Excitonic Nonlinearities in Quantum Wires

physica status solidi (b), 2000

We report on the experimental observation of excitonic molecules (biexcitons) in high-quality Vshaped quantum wires. By means of spatially resolved near-field photoluminescence spectroscopy, first we unambiguously isolate excitons with a one-dimensional character, and secondly we present the optical transition from 1D biexciton to 1D exciton as a function of excitation power density. The density of these biexcitonic molecules is shown to increase superlinearly compared to the linear variation of exciton density.

Exciton dynamics of a single quantum dot embedded in a nanowire

Physical Review B, 2009

We have carried out a detailed optical characterization of a single CdSe quantum dot embedded in a ZnSe nanowire. Exciton, biexciton, and charged exciton lines have been identified unambiguously using photon correlation spectroscopy. This technique has provided a detailed picture of the dynamics of this system. It has been found that the dark exciton has a strong influence on the optical properties. The most visible influence is the strongly reduced excitonic emission compared to the biexcitonic one. Temperature-dependent lifetime measurements have allowed us to measure a large splitting of ⌬E = ͑6.0Ϯ 0.2͒ meV between the dark and the bright exciton as well as the spin-flip rates between these two states. This type of semiconducting quantum dot turns out to be a very efficient single photon source in the visible. Its particular growth technique opens additional possibilities as compared to the usual self-assembled quantum dots.