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We describe the growth, material characterization, and lasing of InP/GaInP quantum dot (QD) microdisks (diameter D = 2.2 μ m, quality factor Q ∼ 9000) with an emission lasing line of 693 nm (77 K). We demonstrate that MOVPE growth can result in two types of InP/GaInP QDs, differing in height (type A h ∼ 5 –10 nm, type B h ∼ 20 nm), whose emission has different decay lifetimes (τ A = 0.6 ns, τ B = 2.4 ns). We show, importantly for technological microlasing applications, that lasing occurs via the excited states of type A QDs, as inferred from a number of experimental results: power-dependent photoluminescence, time-resolved experiments, and temperature dependence of the generation threshold. [ABSTRACT FROM AUTHOR]

In magneto-photoluminescence (magneto-PL) spectra of quasi two-dimensional islands (quantum dots) having seven electrons and Wigner–Seitz radius rs~1.5, we revealed a suppression of magnetic field (B) dispersion, paramagnetic shifts, and jumps of the energy of the emission components for filling factors ν > 1 (B < 10 T). Additionally, we observed B-hysteresis of the jumps and a dependence of all these anomalous features on rs. Using a theoretical description of the magneto-PL spectra and an analysis of the electronic structure of these dots based on the single-particle Fock–Darwin spectrum and many-particle configuration-interaction calculations, we show that these observations can be described by the rs-dependent formation of the anyon (magneto-electron) composites (ACs) involving single-particle states having non-zero angular momentum and that the anyon states observed involve Majorana modes (MMs), including zero-B modes having an equal number of vortexes and anti-vortexes, which can be considered as Majorana anyons. We show that the paramagnetic shift corresponds to a destruction of the equilibrium self-formed ν~5/2 AC by the external magnetic field and that the jumps and their hysteresis can be described in terms of Majorana qubit states controlled by B and rs. Our results show a critical role of quantum confinement in the formation of magneto-electrons and implies the liquid-crystal nature of fractional quantum Hall effect states, the Majorana anyon origin of the states having even ν, i.e., composite fermions, which provide new opportunities for topological quantum computing. [ABSTRACT FROM AUTHOR]

The proposal of fault-tolerant quantum computations, which promise to dramatically improve the operation of quantum computers and to accelerate the development of the compact hardware for them, is based on topological quantum field theories, which rely on the existence in Nature of physical systems described by a Lagrangian containing a non-Abelian (NA) topological term. These are solid-state systems having two-dimensional electrons, which are coupled to magnetic-flux-quanta vortexes, forming complex particles, known as anyons. Topological quantum computing (TQC) operations thus represent a physical realization of the mathematical operations involving NA representations of a braid group Bn, generated by a set of n localized anyons, which can be braided and fused using a "tweezer" and controlled by a detector. For most of the potential TQC material systems known so far, which are 2D-electron–gas semiconductor structure at high magnetic field and a variety of hybrid superconductor/topological-material heterostructures, the realization of anyon localization versus tweezing and detecting meets serious obstacles, chief among which are the necessity of using current control, i.e., mobile particles, of the TQC operations and high density electron puddles (containing thousands of electrons) to generate a single vortex. Here we demonstrate a novel system, in which these obstacles can be overcome, and in which vortexes are generated by a single electron. This is a ~ 150 nm size many electron InP/GaInP2 self-organized quantum dot, in which molecules, consisting of a few localized anyons, are naturally formed and exist at zero external magnetic field. We used high-spatial-resolution scanning magneto-photoluminescence spectroscopy measurements of a set of the dots having five and six electrons, together with many-body quantum mechanical calculations to demonstrate spontaneous formation of the anyon magneto-electron particles (eν) having fractional charge ν = n/k, where n = 1–4 and k = 3–15 are the number of electrons and vortexes, respectively, arranged in molecular structures having a built-in (internal) magnetic field of 6–12 T. Using direct imaging of the molecular configurations we observed fusion and braiding of eν-anyons under photo-excitation and revealed the possibility of using charge sensing for their control. Our investigations show that InP/GaInP2 anyon-molecule QDs, which have intrinsic transformations of localized eν-anyons compatible with TQC operations and capable of being probed by charge sensing, are very promising for the realization of TQC. [ABSTRACT FROM AUTHOR]

We used the measurements of the photo-luminescence spectra vs photon pumping and Coulomb blockade charge tuning together with Kelvin probe microscopy to study piezo-electric fields in self-organized InP/GaInP2 quantum dots (QDs) having a strong Wigner localization regime. These exciton/electron state-filling measurements together with the surface potential imaging and the band structure calculations demonstrate a piezo-electric doping and type-I optical transitions induced in these dots by an atomic ordering (AO) of GaInP2. Our results clarify a critical role of AO in the formation of natural Wigner and anyon molecules and represent an important step for realization of the topological quantum gates using these QDs. [ABSTRACT FROM AUTHOR]

The size and positions of regions of line localization and the magnetic-field (0–10 T) dependence of the low-temperature (10 K) photoluminescence spectra of single InP/GaInP quantum dots with a number of electrons of N = 5–7 and a Wigner–Seitz radius of ~2.5 are determined using a near-field scanning optical microscope. The formation of composite fermion molecules with a size coinciding with that of localization regions and bond lengths of ~30 and 50 nm, respectively, at a Landau-level filling factor from 1/2 to 2/7 in zero magnetic field is established. At N = 6, the pairing and rearrangement of composite fermions under photoexcitation are found, which offers opportunities for the use of InP/GaInP quantum dots to create a magnetic-field-free topological quantum gate. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We used a low temperature near-field scanning optical microscopy (NSOM) to study a formation of Wigner molecules (WMs) in the emission spectra of self-organized InP/GaInP QDs having up to seven electrons. We used a Schottky diode structure for the electrostatic control of the number of the electrons (N) in QD, and we observed the emission of the charged excitons (for N < 3) and of the WMs (for N > 2) in the regime of weak Wigner localization. We show, that a contribution of whispering gallery modes (WGMs) of the electrons and rearrangement of the electrons between the WM and WGM states in the QDs, can explain the anomalous dependence of NSOM image size on the quantum confinement observed for some dots. [ABSTRACT FROM AUTHOR]

A technique of cantilever based scanning near-field optical microscopy is applied. Using InP/GaInP quantum dots structures, 100nm (λ/7) spatial resolution of the technique in illumination-collection regime is tested. The possibility to obtain optical data with a subdiffraction resolution is exploited for clarifying the transversal electric field mode configuration of the radiating semiconductor laser. [ABSTRACT FROM PUBLISHER]

The article reports that exciton localisation in InGaAsN and GaAsSbN observed by near-field magnetoluminescence and scanning optical microscopy (NSOM). Dilute nitride alloys have recently attracted considerable attention as promising materials for laser diodes in the 1.3-1.5 mm range, as well as for more efficient solar cells. The article focuses on use of low-temperature NMPL, at fields up to 10 T, to study these fluctuations in detail. Researchers also employ near-field scanning optical microscopy (NSOM) to study the lateral distribution of such QD-like compositional fluctuations by imaging their individual sharp emission lines.

We report optical measurements (photoluminescence, Raman scattering, and infrared reflectance) of direct band gap and of optical phonon energies of Be[sub x]Zn[sub 1-x]Se alloys grown by MBE on (001) GaAs substrates for a wide range of Be concentrations. The high band gap of BeSe (5.15 eV) suggests the possibility of using isoternary alloys for ultraviolet optoelectronic applications. Be[sub x]Zn[sub 1-x]Se has the unique advantage that it can be lattice matched to Si at about x= 0.5. We observed a strong linear shift of the Be[sub x]Zn[sub 1-x]Se direct band gap to higher energies with increasing Be content (to 3.63 eV for x = 0.34). Furthermore, optical phonon parameters for the entire range of BeSe content have been obtained. Finally, polarized infrared and Raman spectra revealed local atomic ordering (anti-clustering) effects in the group-II sublattice. [ABSTRACT FROM AUTHOR]

The effect of lattice relaxation instability (martensitic transition) on piezoelectric fields (EPE) in spontaneously ordered GaInP2/GaAs epitaxial layers was demonstrated using scanning Kelvin probe microscopy in combination with electron microscopy and optical spectroscopy measurements. The transition manifests itself in the dependence of the surface potential of the epi-layer on the mechanical (cleavage) and thermal (annealing) impacts. This is associated with a switching of the crystal lattice between relaxed and strained martensitic states, corresponding to a change in EPE in the epi-layer. The measured surface potential values (0.2–2.4 V) correspond to EPE within ±100 kV/cm and a strong decrease in |EPE| with increasing layer thickness, indicating the pinning of the Fermi level and piezoelectric doping. Our results open up the prospects for using spontaneously ordered semiconductor alloys to control electronic states in semiconductor nanostructures by controlling their piezoelectric fields. [ABSTRACT FROM AUTHOR]

We used high-spatial-resolution, low-temperature near-field scanning optical microscopy (NSOM) operating at magnetic fields B=0-10T to study the effects of Wigner localization (WL) on emission spectra of single self-organized InP/GaInP quantum dots (QDs) and investigate the stability of singly (trion) and doubly (tetron) charged exciton complexes in the weak quantum confinement regime. Using NSOM measurements together with configuration interaction calculations, we identify the dots having different electron population N(N=1-12), quantum confinement (ℏω0=0.6-8meV) and size D(D=70-170nm). For N=2, we observed a magnetic-field-induced molecular-droplet transition, accompanied by the decomposition of the tetron into a Wigner molecule complex (WMC), and the activation of rotovibronic structure. For N=1, unusually strong vibronic structure resulting from a trion-type WMC was observed. We have shown that magnetic-field-induced shifts of this structure allow measurement of single particle Fock-Darwin levels and angular momentum transitions of the WMC. In addition, we demonstrated the use of NSOM imaging to probe the charge density distribution and observed anomalous dependence of the image size on the quantum confinement, implying a pairing of electrons or formation of whispering gallery modes in the QD. We demonstrated that InP/GaInP QDs, provide a Wigner-Seitz radius (rs) up to 13, and that the measurements of NSOM magneto-optical spectroscopy using these dots makes it possible to study effects arising from strong Coulomb interaction of a few confined electrons (holes). [ABSTRACT FROM AUTHOR]

We report non-contact local doping of a monolayer WSe2 transferred onto a piezoelectric substrate having surface potential wells (SPWs) induced by structural inhomogeneities. We used epitaxial GaN and InP/GaInP2 structures, in which there are SPWs ∼0.2 V deep and 0.1–2 μm in size. Using surface topography and potential scanning probe microscopy, as well as optical reflectance, photoluminescence, and Raman spectroscopy measurements, we observed strong enhancement of charged exciton emission and Raman intensity in the SPW regions of the monolayer WSe2, which indicate on piezoelectric doping at a level n ≥ 1012 cm−2 on a length scale ∼0.2–1 μm. Our results can be used to create electron/hole quantum puddles with anyon states in transition metal dichalcogenides, promising for the development of room temperature and magnetic-field-free fault-tolerant topological quantum computing. [ABSTRACT FROM AUTHOR]

Quantum dots (QDs) formed on GaAs(100) substrates by InAs deposition followed by (Al,Ga)As or (In,Ga,Al)As overgrowth demonstrate a photoluminescence (PL) peak that is redshifted (up to 1.3 μm) compared to PL emission of GaAs-covered QDs. The result is attributed to redistribution of InAs molecules in the system in favor of the QDs, stimulated by Al atoms in the cap layer. The deposition of a 1 nm thick AlAs cover layer on top of the InAs-GaAs QDs results in replacement of InAs molecules of the wetting layer by AlAs molecules, leading to a significant increase in the heights of the InAs QDs, as follows from transmission electron microscopy. This effect is directly confirmed by transmission electron microscopy indicating a transition to a Volmer-Weber-like QD arrangement. We demonstrate an injection laser based on this kind of QDs. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract: We report a realization of room temperature lasing threshold of 1 μW in GaInP microdisk containing a few self-aggregated InP/GaInP quantum dots (QDs) grown by metal-organic vapor phase epitaxy. InP/GaInP QD microdisk cavities emitting in the spectral range of 700-800 nm and having the size of ~2 μm, free spectral range of ~35 nm and quality factors Q ~ 4000 were formed by wet chemical etching. Low dot density (~2 μm-2) and large dot size (~150 nm), suggesting a single dot lasing and maximum overlap of QD and cavity mode, were achieved using deposition of 3 ML of InP layer at 700°C. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Formation, emission, and lasing properties of strain-free InP(As)/AlInAs quantum dots (QDs) embedded in AlInAs microdisk (MD) cavity were investigated using transmission electron microscopy and photoluminescence (PL) techniques. In MD structures, the QDs have the nano-pan-cake shape with the height of ~2 nm, the lateral size of 20-50 nm, and the density of ~5×109 cm-2. Their emission observed at ~940 nm revealed strong temperature quenching, which points to exciton decomposition. It also showed unexpected type-I character, indicating In-As intermixing as confirmed by band structure calculations. We observed lasing of InP(As) QD excitons into whispering gallery modes in MD having the diameter of ~3.2 lm and providing a free spectral range of ~27 nm and quality factors up to Q~13 000. Threshold of ~50 W/cm2 and spontaneous emission coupling coefficient of ~0.2 were measured for this MD-QD system. [ABSTRACT FROM AUTHOR]

The experimentally measured input-output characteristics of optically pumped semiconductor microcavities exhibits unexpected oscillations modifying the fundamentally linear slope in the excitation power regime below lasing. A systematic microscopic analysis reproduces these oscillations, identifying them as a genuine quantum-memory effect, i.e., a photon-density correlation accumulated during the excitation. With the use of projected quantum measurements, it is shown that the input-output oscillations can be controlled and enhanced by an order of magnitude when the quantum fluctuations of the pump are adjusted. [ABSTRACT FROM AUTHOR]

Optical and light-emitting diode structures with an active InGaN region containing short-period InGaN/GaN superlattices are studied. It is shown that short-period superlattices are thin two-dimensional layers with a relatively low In content that contain inclusions with a high In content 1–3 nm thick. Inclusions manifest themselves from the point of view of optical properties as a nonuniform array of quantum dots involved in a residual quantum well. The use of short-period superlattices in light-emitting diode structures allows one to decrease the concentration of nonradiative centers, as well as to increase the injection of carriers in the active region due to an increase in the effective height of the AlGaN barrier, which in general leads to an increase in the quantum efficiency of light-emitting diodes. [ABSTRACT FROM AUTHOR]

InGaN quantum dot (QD) formation in a wide pressure range MOCVD reactor was studied. The existence of QDs and their lateral size (2–5 nm) were demonstrated using transmission electron microscopy and high spatial resolution (~ 100 nm) near-field magneto-photoluminescence spectroscopy. We found that an increase of the reactor pressure from 400 to 1000 mbar leads to an order of magnitude increase in light emission efficiency of the InGaN/GaN QDs accompanied by ~ 100 meV redshift of the emission wavelength. We explored stimulated phase separation (SPS) to control carrier localization and emission wavelength. The SPS was achieved by adding In in the matrix material. This leads to formation of extremely deep InGaN/InGaN QDs having energy localization up to ~ 0.8 eV, which was revealed from selectively excited far-field photoluminescence (PL) spectra. Without SPS the QD activation energy is found to be below 0.2 eV. A nonequilibrium carrier population strongly suppresses the temperature-induced shift of the PL emission in deep InGaN QDs. [ABSTRACT FROM AUTHOR]

We have investigated the influence of Si–N complexes on the electronic properties of GaAsN alloys. The presence of Si–N complexes is suggested by a decrease in carrier concentration, n, with increasing N-composition, observed in GaAsN:Si films but not in modulation-doped heterostructures. In addition, for GaAsN:Te (GaAsN:Si), n increases substantially (minimally) with annealing-T, suggesting a competition between annealing-induced Si–N complex formation and a reduced concentration of N-related traps. Since Si–N complex formation is enhanced for GaAsN:Si growth with the (2×4) reconstruction, which has limited group V sites for As–N exchange, the (Si–N)As interstitial pair is identified as the dominant Si–N complex. [ABSTRACT FROM AUTHOR]

We have studied the optical properties of pseudo-alloy monolayer InAs/GaAsN superlattices with highly planar interfaces. In spite of the two-dimensional growth mode, we found that the photoluminescence (PL) reveals strong exciton localization through the whole PL band, dominating the spectrum up to high excitation densities and observation temperatures. Pump-and-probe PL experiments provide the following time constants: (a) the exciton relaxation time to the ground states of the localization regions is found to be ∼40–70 ps, depending on the photon energy, and (b) the time for depopulation of these localized states is between 2 and 4 ns. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]