Influence of free carriers on exciton ground states in quantum wells

The influence of free carriers on the ground state of the exciton at zero magnetic field in a quasi-two-dimensional quantum well doped with electrons is considered in the framework of the random phase approximation. The effects of the exciton-charge-density interaction and the inelastic scattering processes due to the Hartree-Fock electron-electron exchange interaction are taken into account. The effect of phase-space filling is considered using an approximate approach. The results of the calculation are compared with the experimental data available.Comment: 8 pages, 5 fugure

Manifestation of interface anisotropy in CdTe quantum wells

Photoluminescence and polarized reflection spectra of quantum well structures with symmetric Cd$_{0.9}$Zn$_{0.1}$Te/CdTe/Cd$_{0.9}$Zn$_{0.1}$Te and asymmetric Cd$_{0.9}$Zn$_{0.1}$Te/CdTe/Cd$_{0.4}$Mg$_{0.6}$Te barriers were studied. The Stokes parameters of the reflected light from these structures were measured. In the structures with symmetric barriers, exciton resonances were found in the reflection spectra and were not present in the photoluminescence spectra. In structures with asymmetric barriers, in the region of exciton resonances, the phenomenon of light birefringence was detected, caused by a lower symmetry of the interfaces compared to the symmetry of bulk crystals. A discussion of both phenomena was given

Optical Study of GaAs quantum dots embedded into AlGaAs nanowires

We report on the photoluminescence characterization of GaAs quantum dots embedded into AlGaAs nano-wires. Time integrated and time resolved photoluminescence measurements from both an array and a single quantum dot/nano-wire are reported. The influence of the diameter sizes distribution is evidenced in the optical spectroscopy data together with the presence of various crystalline phases in the AlGaAs nanowires.Comment: 5 page, 5 figure

Observation of Spin Relaxation Anisotropy in Semiconductor Quantum Wells

Spin relaxation of two-dimensional electrons in asymmetrical (001) AlGaAs quantum wells are measured by means of Hanle effect. Three different spin relaxation times for spins oriented along [110], [1-10] and [001] crystallographic directions are extracted demonstrating anisotropy of D'yakonov-Perel' spin relaxation mechanism. The relative strengths of Rashba and Dresselhaus terms describing the spin-orbit coupling in semiconductor quantum well structures. It is shown that the Rashba spin-orbit splitting is about four times stronger than the Dresselhaus splitting in the studied structure.Comment: 4 pages, 3 figure

Phase diagrams of magnetopolariton gases

The magnetic field effect on phase transitions in electrically neutral bosonic systems is much less studied than those in fermionic systems, such as superconducting or ferromagnetic phase transitions. Nevertheless, composite bosons are strongly sensitive to magnetic fields: both their internal structure and motion as whole particles may be affected. A joint effort of ten laboratories has been focused on studies of polariton lasers, where non-equilibrium Bose-Einstein condensates of bosonic quasiparticles, exciton-polaritons, may appear or disappear under an effect of applied magnetic fields. Polariton lasers based on pillar or planar microcavities were excited both optically and electrically. In all cases a pronounced dependence of the onset to lasing on the magnetic field has been observed. For the sake of comparison, photon lasing (lasing by an electron-hole plasma) in the presence of a magnetic field has been studied on the same samples as polariton lasing. The threshold to photon lasing is essentially governed by the excitonic Mott transition which appears to be sensitive to magnetic fields too. All the observed experimental features are qualitatively described within a uniform model based on coupled diffusion equations for electrons, holes and excitons and the Gross-Pitaevskii equation for exciton-polariton condensates. Our research sheds more light on the physics of non-equilibrium Bose-Einstein condensates and the results manifest high potentiality of polariton lasers for spin-based quantum logic applications.Comment: 21 pages, 11 figure

Optical Method for Determination of Carrier Density in Modulation Doped Quantum Wells

An optical method is suggested to determine the concentration of two-dimensional electrons in modulation-doped quantum wells at low and moderate electron densities between 10^{9} and 2x10^{11} cm^{-2}. The method is based on an analysis of magneto-reflectivity spectra of charged excitons (trions). The circular polarization degree and the oscillator strength of the charged excitons contain information about the density and spin polarization of two-dimensional electron gas. The method is applied to CdTe/(Cd,Mg)Te and ZnSe/Zn,Mg)(S,Se) heterostructures