Photoluminescence Of Single Quantum Dots Research Articles

Tuning Single Quantum Dot Emission with a Micromirror.

The photoluminescence of single quantum dots fluctuates between bright (on) and dark (off) states, also termed fluorescence intermittency or blinking. This blinking limits the performance of quantum dot-based devices such as light-emitting diodes and solar cells. However, the origins of the blinking remain unresolved. Here, we use a movable gold micromirror to determine both the quantum yield of the bright state and the orientation of the excited state dipole of single quantum dots. We observe that the quantum yield of the bright state is close to unity for these single QDs. Furthermore, we also study the effect of a micromirror on blinking, and then evaluate excitation efficiency, biexciton quantum yield, and detection efficiency. The mirror does not modify the off-time statistics, but it does change the density of optical states available to the quantum dot and hence the on times. The duration of the on times can be lengthened due to an increase in the radiative recombination rate.

CdTe/Zn(Mg)(Se)Te quantum dots for single photon emitters grown by MBE

We report on pseudomorphic MBE growth of CdTe/Zn(Mg)(Se)Te quantum dot (QD) structures on InAs(100) substrates and studies of their structural and optical properties. The QDs were fabricated by using a thermal activation technique comprising deposition of a strained CdTe 2D layer, covering it with amorphous Te, followed by fast thermal desorption of the Te layer, which results in a 2D-3D RHEED pattern transition. The QDs exhibit the surface density as low as ~1010cm−2. The influence of MBE growth parameters and the structure design on photoluminescence properties of the QDs are discussed. Single QD photoluminescence was observed at T=8K from the 200-nm-wide mesa-structures made of the CdTe QD structures, and the antibunching effect with g(2)(0)=0.16±0.04 was demonstrated. The peculiarities of MBE growth of ZnTe/MgTe/MgSe short-period superlattices nearly lattice-matched to InAs, which could serve as wide gap barriers for efficient electron and hole confinement in the CdTe/Zn(Mg)(Se)Te QDs, are also described.

Efficient Emission from InAlGaAs Single Quantum Dots with Low Lattice Misfit and AlGaAs Indirect Bandgap Barrier

We report on molecular beam epitaxy growth and properties of rarely studied quaternary In0.4(Al0.75Ga0.25)0.6As self-assembled quantum dots, which show strong and efficient emission of red light from single quantum dots. The increased yield is, among others, due to efficient energy transfer from indirect band-gap Al0.75Ga0.25As barriers. To maximize photon energy emitted from quantum dots, low In composition, xIn = 0.4 was applied, which also lowered the lattice misfit close to the limit of 2D/3D transition in the Stranski–Krastanov growth mode. Time-resolved micro-photoluminescence shows emission at 650–750 nm. Well-resolved single quantum dot photoluminescence lines (decay time of ≈ 1−2 ns) are observed despite a high concentration ≈ 3 × 10 cm−2 of quantum dots. We discuss this observation assuming newly a role of carriers or excitons diffusion/tunneling between quantum dots at high surface concentration of dots and a possible role of lattice disorder inside the dot on the exciton lifetime.

Photoluminescence of single quantum dots in microcavities

We study theoretically the photoluminescence of a single quantum dot in a microcavity under incoherent excitation. Analytical results including pure dephasing show that strong coupling and linewidths are largely independent on the pumping intensity (until saturation effects come into play). We show the reliable predicting character in the analysis of some experiments.

Comparison of the photoluminescence properties of semiconductor quantum dots and non-blinking diamond nanoparticles. Observation of the diffusion of diamond nanoparticles in living cells

Long-term observations of photoluminescence at the single-molecule level were until recently very diffcult, due to the photobleaching of organic ?uorophore molecules. Although inorganic semiconductor nanocrystals can overcome this diffculty showing very low photobleaching yield, they suffer from photoblinking. A new marker has been recently introduced, relying on diamond nanoparticles containing photoluminescent color centers. In this work we compare the photoluminescence of single quantum dots (QDs) to the one of nanodiamonds containing a single-color center. Contrary to other markers, photoluminescent nanodiamonds present a perfect photostability and no photoblinking. At saturation of their excitation, nanodiamonds photoluminescence intensity is only three times smaller than the one of QDs. Moreover, the bright and stable photoluminescence of nanodiamonds allows wide field observations of single nanoparticles motion. We demonstrate the possibility of recording the tra jectory of such single particle in culture cells.

Electrical charging of a single quantum dot by a spin polarized electron

Voltage controlled electrical charging of a single InAs quantum dot by a spin polarized electron from a ZnMnSe spin aligner is presented, and the spin information is read out optically. We demonstrate that the characteristic single quantum dot photoluminescence polarization pattern of the negative trion and the neutral exciton lines directly reflects the spin state of the electrically injected electron.

Green photoluminescence of single InP-quantum dots grown on [formula omitted]InP/AlInP distributed Bragg reflectors

We demonstrate the growth of an Al 0.66 Ga 0.33 InP/AlInP distributed Bragg reflector (DBR) for wavelengths around 570 nm at 5 K. The DBR was used for light enhancement of self-assembled InP-quantum dots embedded in Al 0.7 Ga 0.3 InP where we detected single quantum dot photoluminescence in the green spectral region.

Optical study of single InAs on In0.12Ga0.88As self-assembled quantum dots: biexciton binding energy dependence on the dots size

Single self-assembled InAs quantum dots embedded in a In0.12Ga0.88As quantum well and emitting in the near infrared have been optically investigated. The dependence on the excitation power of the single quantum dot photoluminescence has been used to identify the emission of the biexciton complex. The biexciton binding energy, which has been measured for a dozen dots, increases with increasing exciton transition energy for the dot sizes investigated in the present work, as a consequence of stronger confinement in a smaller quantum dot. The obtained data is compared with experimental results available in the literature for InAs quantum dots.

Spin injection into a single self-assembled quantum dot

We demonstrate spin injection into a single self-assembled CdSe/ZnSe quantum dot using a semimagnetic BeMnZnSe spin aligner. Comparing quasiresonant excitation of the single quantum dot to excitation above the spin-aligner band gap, spin injection is evidenced by a strong increase of the polarization degree of the single quantum dot photoluminescence emission even at small magnetic fields. A spin injection efficiency into a single quantum dot of about 70% can be estimated. From a detailed analysis of the polarization degree, we derive an exciton spin-relaxation time from the upper to the lower Zeeman level of about a nanosecond in the quantum dot, independent of magnetic field.

Carrier–carrier interaction in single In0.5Ga0.5As quantum dots at room temperature investigated by near-field scanning optical microscope

We describe carrier–carrier interaction in self-assembled In0.5Ga0.5As quantum dots (QDs) at room temperature. The spectral shift and linewidth broadening of ground state emission as a function of the excitation density are investigated through near-field single quantum dot photoluminescence spectroscopy. From the viewpoint of excitation density dependent spectral broadening of the ground state emission, we discuss the dephasing process in QDs due to Coulomb interaction.

Dark exciton signatures in time-resolved photoluminescence of single quantum dots

ABSTRACTTime-resolved photoluminescence of single charge tuneable quantum dots allows us to probe the differences in recombination dynamics between neutral and negatively charged excitons. We find that the luminescence decay from a neutral exciton contains a second lifetime component of several nanoseconds that is not present in the luminescence from singly or doubly charged excitons. We attribute the slowly decaying component to excitation cycles in which the initial exciton formed in the dot is dark, with angular momentum M = 2, and which subsequently scatters into the bright state with M = 1.The nature of the scattering mechanism is revealed by the dependence of the lifetime on the electrical bias applied across the charge-tuneable device. That the lifetime changes by an order of magnitude within a short bias range implies that the dark-to-bright transmutation does not occur through a simple spin flip. Rather it appears to come about by the dot briefly entering a higher energy charging state which allows exchange of the existing electron with another from the n-type contact region. We model the lifetimes and relative intensities of the two decay components using a simple rate equation analysis.

Optical anisotropy of self-assembled InGaAs quantum dots embedded in wall-shaped and air-bridge structures

Strain effect on optical anisotropy of quantum dots has been investigated by changing the surrounding matrix of the dots. Optical anisotropy can be induced by lateral patterning of the matrix of the dots, although such anisotropy is absent in the as-grown dots. A reduction of the optical anisotropy is observed by changing the laterally patterned structure into a free-standing structure or an air bridge. The optical anisotropy is mainly attributed to strain asymmetry in the fabricated structures. The presence of the strain asymmetry is confirmed by the observation of a doublet fine structure in spectrally resolved photoluminescence of single quantum dots.