We performed comparative optical spectroscopic studies of the excitonic spectrum in self-organized InAs/Al0.3Ga0.7As and InAs/GaAs quantum dots. The exciton excited states were revealed by either measuring photoluminescence spectra using different excitation pump powers or by carrying out selective resonant excitation of the quantum dot photoluminescence through the excited states. As a result, we evaluated average energies of the excitonic transitions and elucidated dominant mechanisms of exciton relaxation from the excited states to the ground one for both types of quantum dots.

We measure low-temperature micro-photoluminescence spectra along a MoS$_2$ nanotube, which exhibit the peaks of the optical whispering gallery modes below the exciton resonance. The variation of the position and intensity of these peaks is used to quantify the change of the nanotube geometry. The width of the peaks is shown to be determined by the fluctuations of the nanotube wall thickness and propagation of the detected optical modes along the nanotube. We analyse the dependence of the energies of the optical modes on the wave vector along the nanotube axis and demonstrate the potential of the high-quality nanotubes for realization of the strong coupling between exciton and optical modes with the Rabi splitting reaching 400 meV. We show how the formation of exciton-polaritons in such structures will be manifested in the micro-photoluminescence spectra.

Microphotoluminescence (μPL) spectra of single In(Ga)P/GaInP quantum dots (QD) were investigated. Measurements were carried out at different optical pump power and at different electric field with constant optical pump. Filling of electron s-, p-, d-states was observed. Quantum confinement Stark effect (QCSE) was detected. Obtained PL life times of s-, p- electron states were 0.5 ns and 0.4 ns respectively. From spectra it is clearly seen that QDs have weak quantum confinement (hω0∼4-8meV).

The anisotropic exchange splitting of the Gamma exciton delta(1) is measured in (In,Al)As/AlAs quantum dots with a type-I band alignment by means of two photoluminescence techniques: The macroscopic technique exploits the competition between the anisotropic exchange interaction and the Zeeman splitting, whereas with the microscopic technique the energy splitting of the exciton fine-structure in a single quantum dot is measured directly. We find that in the spectral region of the Gamma X mixing the anisotropic exchange splitting decreases strongly.

The statistics of photon correlations in the emission of single InAs/AlGaAs quantum dots grown by molecular beam epitaxy and fitted with AlGaAs waveguide nanoantennas for efficient extraction of radiation is investigated. A single-photon source for the red spectral range with an average emission rate exceeding 5 MHz and a zero-delay second-order correlation function of g (2) (0) = 0.08 is realized on the basis of these photonic nanostructures. The degree of indistinguishability of consecutively emitted photons measured in Hong-Ou-Mandel interferometry under above-barrier excitation is about 30%.

We used transmission electron microscopy, Raman, and photoluminescence spectroscopy to identify the effect of CuPt-type GaP-InP atomic ordering (AO) on the structural and emission properties of self-organized (SO) InP/GaInP2 Wigner molecule (WM) quantum dot (QD) structures. We found that the correlation of AO and SO growth results in the formation of InP/GaInP2 QD/AO-domain (QD/AOD) core-shell composites. This observation shows that intrinsic WMs in this system emerge due to a strong piezoelectric field generated by AODs, which induces QD doping and a built-in magnetic field. We found that the bond relaxation of AODs leads to a decrease in the emission energy of WMs of 80 meV. The photoluminescence spectra of single WMs having an emission energy ∼1.53 eV are presented here, the lowest one reported for this system.

Using time-resolved photoluminescence (PL) spectroscopy, we establish the presence of the Förster energy transfer mechanism between two arrays of epitaxial CdSe/ZnSe quantum dots (QDs) of different sizes. The mechanism operates through dipole–dipole interaction between ground excitonic states of the smaller QDs and excited states of the larger QDs. The dependence of energy transfer efficiency on the width of barrier separating the QD insets is shown to be in line with the Förster mechanism. The temperature dependence of the PL decay times and PL intensity suggests the involvement of dark excitons in the energy transfer process.

We report on single photon emission with a wavelength below 500 nm from single CdSe quantum dots (QDs) grown by migration-enhanced epitaxy providing a reduced QD lateral density below 1010 cm-2. The QD photoluminescence was observed at the temperature of 8 K in 200-nm-wide mesa-structures made of CdSe QD heterostructures. The antibunching effect under cw excitation with g(2)(0) ˜ 0.2 was demonstrated.

We investigated structural and emission properties of self-organized InP/GaInP quantum dots (QD) grown by metal organic chemical vapor deposition using an amount of deposited In from 7 to 2 monolayers (ML). In the uncapped samples, using atomic force microscopy (AFM), we observed lateral sizes of 100–200 nm, together with a bimodal height distribution having maxima at ∼5 and ∼15 nm, which we denoted as QDs of type A and B, respectively; and reduction of the density of the type-B dots from 4.4 to 1.6 μm –2 . The reduction of the density of B-type dots were observed also using transmission electron microscopy of the capped samples. Using single dot low-temperature photoluminescence (PL) spectroscopy we demonstrated effects of Wigner localization for the electrons accumulated in these dots.

The emission characteristics of a source of single photons based on an epitaxial heterostructure with CdSe/ZnSe quantum dots and a cylindrical waveguide with a varying cross section formed in a resist layer by electron-beam lithography are investigated. It is shown that a flux of single photons at a wavelength of 530 nm with an average rate of about 1 MHz and the value g ( 2 )(0) = 0.15 ± 0.03 of the second-order correlation function at zero delay can be generated under optical pumping at 80 K.

Data on the molecular beam epitaxy (MBE) technology, design, and luminescent properties of heterostructures with CdTe/Zn(Mg)(Se)Te quantum dots on InAs(001) substrates are presented. X-ray diffraction has been used to study short-period ZnTe/MgTe/MgSe superlattices used as wide-bandgap barriers in structures with CdTe/ZnTe quantum dots for the effective confinement of holes. It is shown that the design of these superlattices must take into account the replacement of Te atoms by selenium on MgSe/ZnTe and MgTe/MgSe heterointerfaces. Heterostructures with CdTe/Zn(Mg)(Se)Te quantum dots exhibit photoluminescence at temperatures up to 300 K. The spectra of microphotoluminescence at T = 10 K display a set of emission lines from separate CdTe/ZnTe quantum dots, the surface density of which is estimated at ~1010 cm−2.

We report on fabrication by molecular beam epitaxy and optical studies of hybrid semiconductor-dielectric micropillar structures with distributed Brag reflectors and a microcavity containing InAs/AlGaAs quantum dots. The single photon emission in the visible spectral range with the autocorrelation function g((2))(0)<0.2 is detected in such structures with a photon count rate above 1 MHz.

We report on single-photon emission of InAs/AlGaAs self-assembled quantum dots (QDs) grown by molecular beam epitaxy. By varying the growth conditions the QDs luminescence could be tuned over a wide wavelength range from 0.64 to 1 μm, including red part of the visible spectrum. Emission properties of individual QDs are investigated by micro-photoluminescence (μ-PL) spectroscopy using 500-nm-size etched mesa structures. Autocorrelation functions of photons from single QDs, measured in the wide spectral range demonstrate antibunching effect at zero delay time with a value of g(2)(0) ~ 0.17 that is a clear evidence of non-classical light.

Structural and emission properties of few-electron In(Ga) P/GaInP quantum dots (QDs) representing natural Wigner molecules (WM) and whispering gallery mode (WGM) electron (e) cavities have been investigated. QD structures were grown using self-organized metal-organic vapor phase epitaxy and deposition from similar to 3 to 7 monolayers of InP at 700 degrees C. Using atomic force microscopy, transmission electron microscopy, near-field scanning optical microscopy (NSOM), and mu-photoluminescence (mu-PL) spectra we obtained In(Ga) P/GaInP QDs having lateral size 80-180 nm, height 5-30 nm, Ga content 0.0-0.4, density 2-10 mu m(-2), and electron population up to 20 and demonstrated control of their density and size distribution. Using high-spatial-resolution low-temperature PL spectra, NSOMimaging, and calculations of charge density distributions we observed Wigner localization and e-cavity effects for a series of dots having quantum confinement h omega(0) = 0.5-6 meV. We used these data together with time-resolved PL measurements to clarify the effect of Coulomb interaction and WM formation on emission spectra of few-electron QDs. We present direct observation of 2e, 6e, and 9e WMs; 2e and 4e WGMs; and Fabry-Perot e modes and establish conditions of e-WGM-cavity formation in these QDs.

We report on micro-photoluminescence studies of InAs/AlGaAs single self-assembled quantum dots grown by molecular beam epitaxy. A variation of the exciton fine structure splitting induced by the anisotropic part of the electron-hole exchange interaction is systematically studied depending on the exciton emission energy and the insertion of a GaAs interlayer prior formation of the InAs QDs.

We report on Förster resonance energy transfer in the dense arrays of epitaxial quantum dots (QDs), formed by fractional monolayer CdSe insertions within a ZnSe matrix. In such arrays comprising the QDs of different sizes, the energy transfer can take place between the ground levels of small QDs and the excited levels of large radiating QDs, when these states are in resonance. This mechanism provides directional excitation of a limited number of the large QDs possessing the excited levels. It reveals itself by the shrinkage of photoluminescence (PL) bands and the appearance of the narrow single excitonic lines in micro-PL spectra. The strong shortening of characteristic PL decay times in the energy-donating QDs is observed when the distance between them and the energy-accepting QDs decreases. Photoluminescence excitation spectroscopy demonstrates the switching of the dominant energy transfer mechanism at the energy predicted by theoretical modeling of the excitonic levels in the QD arrays. Our results pave the way for engineering of the architecture of excitonic levels in the QD arrays to realize efficient nano-emitters.

We report on micro-photoluminescence studies of individual self-organized CdTe/ZnTe quantum dots intended for single-photon-source applications in a visible spectral range. The quantum dots surface density below 10(10) per cm(2) was achieved by using a thermally activated regime of molecular beam epitaxy that allowed fabrication of etched mesa-structures containing only a few emitting quantum dots. The single photon emission with the autocorrelation function g((2))(0)<0.2 was detected and identified as recombination of charged excitons in the individual quantum dot.

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.

We report on single photon emission from single CdTe/ZnTe quantum dots (QDs) grown by thermally-activated molecular beam epitaxy providing a reduced QD lateral density below 10(10) cm(-2). For micro-photoluminescence spectroscopy studies and correlation measurements, the mesa structures of 200 and 500 nm diameters are fabricated by combination of electron-beam lithography and reactive plasma etching. Autocorrelation function of photons emitted from a single QD under cw excitation demonstrates antibunching with a value of g((2))(0) similar to 0.3 that is a signature of non-classical light.

We report on emission properties of single-photon sources of visible light, based on InAs/AlGaAs, CdTe/ZnTe, and CdSe/ZnSe quantum dot (QD) heterostructures grown by molecular beam epitaxy. For all types of QDs, the studies performed by micro-photoluminescence and photon correlation spectroscopies demonstrated the single-photon nature of emission with typical values of the second-order correlation function g((2)) (0) less than 0.2 and allowed evaluation of sub-microsecond kinetics of blinking governed by local charging effects.