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In gate-defined quantum dot systems, the conductance change of electrostatically coupled sensor dots allows the observation of the quantum dots' charge and spin states. Therefore, the sensor dot must be optimally sensitive to changes in its electrostatic environment. A series of conductance measurements varying the two sensor-dot-forming barrier gate voltages serve to tune the dot into a corresponding operating regime. In this article, we analyze the noise characteristics of the measured data and define a criterion to identify continuous regions with a sufficient signal-gradient-to-noise ratio. Hence, accurate noise estimation is required when identifying the optimal operating regime. Therefore, we evaluate several existing noise estimators, modify them for 1-D data, optimize their parameters, and analyze their quality based on simulated data. The estimator of Chen et al. turns out to be best suited for our application concerning minimally scattering results. Furthermore, using this estimator in an algorithm for flank-of-interest classification in measured data shows the relevance and applicability of our approach.

This paper reports the fabrication of a broadband near-infrared response (vis-NIR) photodetector (PD) using Cu2SnS3 (CTS) quantum dots (QDs) as photoactive semiconductor material and graphene as a carrier transport medium. The QDs of earth abundant, nontoxic, and inexpensive CTS have been synthesized by solvothermal method, and the chemical vapor deposition (CVD) technique is used to synthesize few layers and monolayers of graphene. The fabricated CTS QDs/graphene/SiO2/Si PD demonstrated high values of responsivity (~110.089 A/W), detectivity ($\sim 1.25 \times 10^{{12}}\,\,\text {cm} \cdot \text {Hz}^{\text {1/2}} \cdot \text {W}^{-{1}}$), and quantum efficiency (~160.9) for broadband (vis-NIR) region due to high absorption coefficient of CTS QDs and very high mobility (~200 000 cm2/V–s) of graphene. The time-response analysis of PD was also performed under vis-NIR and ON and OFF time were found to be 10.2 and 11.34 s. [ABSTRACT FROM AUTHOR]

This Special Issue is associated with the 10th International Conference on Materials for Advanced Technologies (ICMAT), Symposium C: Semiconductor Photonics held on 23–28 June, 2019 at Marina Bay Sands in Singapore. Organised through the Materials Research Society of Singapore (MRS-S), ICMAT has been held since 2001 and has attracted strong interest amongst the global materials science and engineering research communities. The 10th conference in the ICMAT series attracted over 3,500 delegates with a number of keynote and plenary presentations notably including four Nobel Laureates in Physics and Chemistry. The ICMAT conference consists of a number of topical symposia. Symposium C was organized jointly with Australian MRS and co-chaired by Professors Dao-Hua Zhang (NTU, Singapore), Chennupati Jagadish (ANU, Australia), Stephen J. Sweeney (University of Surrey, UK), Boon S. Ooi (KAUST, Saudi Arabia), Hao Gong (NUS, Singapore) and Weijun Fan (NTU, Singapore). The Symposium focused on recent developments in materials for applications in photonic devices covering systems including III-V and II-VI semiconductors, group IV alloys for silicon compatibility, oxides and perovskites for solar cell and emitter applications, quantum dot based devices and in general a wide variety of organic and inorganic materials spanning applications from the ultra-violet through to the mid-infrared. In total, 20 invited and 53 oral and 19 poster papers were presented over the four days of technical sessions. [ABSTRACT FROM AUTHOR]

An approach is proposed to realize large-scale, “high-temperature” and high-fidelity quantum computing integrated circuits based on single- and multiple-coupled quantum-dot electron- and hole-spin qubits monolithically integrated with the mm-wave spin manipulation and readout circuitry in a commercial CMOS technology. Measurements of minimum-size 6 nm $\times20$ nm $\times80$ nm Si-channel n-MOSFETs (electron-spin qubit), SiGe-channel p-MOSFETs (hole-spin qubit), and double quantum-dot complementary qubits reveal strong quantum effects in the subthreshold region at 2 K, characteristic of resonant tunneling in a quantum dot. S-parameter measurements of a transimpedance amplifier (TIA) for spin readout show an improved performance from 300 K to 2 K. Finally, the qubit-with-TIA circuit has 50- $\Omega $ output impedance and 78-dB $\Omega $ transimpedance gain with a unity-gain bandwidth of 70 GHz and consumes 3.1 mW. [ABSTRACT FROM AUTHOR]

We experimentally study the pulse generation and the pulse train timing and amplitude stability of a monolithic passively mode-locked multisection quantum-well semiconductor laser. The laser emits a stable optical pulse train at a wavelength of 1070 nm and at a fundamental repetition rate of 20 GHz. Timing jitter and amplitude jitter analysis allows identifying distinct laser operating regimes of stable picosecond optical pulses. We obtain an ultra-low pulse-to-pulse timing jitter of 22 fs and find emission regimes which are unaffected by amplitude jitter. The lowest pulse width amounts to 2.6 ps, and the highest pulse peak power is estimated to be 556 mW at a low timing jitter of 170 fs and a negligible relative amplitude jitter of 0.05. [ABSTRACT FROM AUTHOR]

The dynamical properties of InP-based quantum dot (QD) gain media are surveyed and analyzed for three time scales ranging from tens of picoseconds to less than 200 fs, where quantum coherent phenomena are observable. Each of these time scales determines the important properties of QD devices, i.e., modulation capabilities, nonlinear gain, and coherent light-matter interactions. Experimental investigations and modeling results are described, highlighting the state of the art in QD devices for the important 1550-nm telecom wavelength range.

A picosecond-range timing of charged particles and photons is a long-standing challenge for many high-energy physics, biophysics, medical and security applications. We present a design, technological pathway and challenges, and some properties important for realization of an ultrafast high-efficient room-temperature semiconductor scintillator based on self-assembled InAs quantum dots (QD) embedded in a GaAs matrix. Low QD density (< 10^15~\cm^-3), fast (\sim 5~\ps) electron capture, luminescence peak redshifted by 0.2-0.3 eV from GaAs absorption edge with fast decay time (0.5-1 ns) along with the efficient energy transfer in the GaAs matrix (4.2 eV/pair) allows for fabrication of a semiconductor scintillator with the unsurpassed performance parameters. The major technological challenge is fabrication of a large volume ( > 1~\cm^3) of epitaxial QD medium. This requires multiple film separation and bonding, likely using separate epitaxial films as waveguides for improved light coupling. Compared to traditional inorganic scintillators, the semiconductor-QD based scintillators could have about 5x higher light yield and 20x faster decay time, opening a way to gamma detectors with the energy resolution better than 1% and sustaining counting rates > 100~\MHz. Picosecond-scale timing requires segmented low-capacitance photodiodes integrated with the scintillator. For photons, the proposed detector inherently provides the depth-of-interaction information. [ABSTRACT FROM AUTHOR]

We report a quantum dot (QD)-based light emitting diode (LED) structure with a solution processed zinc oxide electron transporting layer, with patterning of anode and cathode on the substrate toward cellular imaging applications. Compared with the use of sputtered thin films, solution processed electron transporting layer improves robustness of the device, as crystalline ZnO shows low CB and VB edge energy levels, efficiently suppressing hole leakage current resulting in LEDs with longer lifetimes. We demonstrate a working lifetime of more than 12 h and a shelf-life of more than 180 days for the devices. Our solution-based process is applicable to microcontact printed and also spin-coated QD films. Further, we demonstrate electroluminescence of QD LEDs at 580and 600-nm emission wavelengths, with typical turn-ON voltage of 12 V. We compare operating characteristics of an array of individually addressable LEDs fabricated on a single substrate, with average size of each element being 800 μm × 200 μm. The LEDs with spin-coated ETL show a lifetime increase of more than three orders of magnitude compared with devices made using sputtered ETL layer. We find marginal increases in the intensity and uniformity of devices fabricated using a spin-coated ZnO layer. Finally, we demonstrate a compact multicolor light source for cell characterizations by imaging HEMA 3 stained MDA-MB 231 breast cancer cells on-chip. We demonstrate the capability of the devices as a light source by measuring intensity across stained cells with QDLEDs of two different wavelengths and show the correlation as expected with the absorption profile of the fluorescent dye. [ABSTRACT FROM PUBLISHER]

We describe an unsaturated gain-loss model in regards to colloidal PbSe quantum dot (QD)-doped fiber laser realized previously. Based on experimental observation on the laser, the numerical simulation on the model indicates there exists a pumping threshold that depends on the QD doping concentration. There is a defined range of doping concentration, within which the laser can be generated. Available doping density depends on the fiber length, following an exponential decrease with the increased fiber length. Our model suggests a reasonable lifetime of 100 ns for the upper level of QDs in the background of UV curing adhesive, which is shorter than the lifetime reported in literatures. [ABSTRACT FROM AUTHOR]

We simulate spin wave (SW) dynamics in a thin film antidot magnonic crystal (MC) with a ring defect. An external magnetic field is applied perpendicular to the film plane in a forward volume configuration. We initially use the plane wave method to obtain the SW band diagram for the antidot MC structure (without the defect), which gives us an idea of modes that are trapped in the crystal. We then use finite element micromagnetic simulations to study the SW propagation in the MC with the ring defect. The power spectral density of the magnetization at the top of the ring shows peaks that fall within the band gap of the MC. The SW energy in other frequency components is dissipated in the MC and do not reach the other end of the ring. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the linear and nonlinear photoabsorption processes in the conduction-band-confined levels of a singly charged ZnO quantum dot (QD) surrounded by HfO2 and AlN matrices. We also investigate the photoelectric process in which the conduction band electron ejects from the dot to the vacuum. We use the effective mass approximation with a finite barrier height at the dot-matrix interface. We consider the self-energy of the electron in the dot and the local field effect. The electromagnetic interaction of the incident radiation with the electron in the dot is considered in the electric dipole plus quadrupole approximation. Results for the photoabsorption coefficient and the photoelectric process are presented for different dot sizes and different intensities of incident radiation. It is found that the inclusion of the quadrupole effect reveals new photoabsorption peaks in the absorption spectra. Both the photoabsorption and photoelectric processes significantly depend on the dot size and the surrounding matrix. The change in the intensity of the incident radiation significantly influences the nonlinear photoabsorption. The photoabsorption coefficient and the photoelectric cross sections are found to be relatively higher for the ZnO QD embedded in the high-dielectric constant matrix HfO2 as compared with the lower-dielectric constant AlN matrix. [ABSTRACT FROM PUBLISHER]

The modulation dynamics and the linewidth enhancement factor of excited-state (ES) lasing quantum dot (QD) semiconductor lasers are investigated through a set of improved rate equation model, in which the contribution of off-resonant states to the refractive index change is taken into account. The ES laser exhibits a broader modulation response associated with a much lower chirp-to-power ratio in comparison with the ground-state (GS) lasing laser. In addition, it is found that the laser emission in ES reduces the linewidth enhancement factor of QD lasers by about 40% than that in GS. These properties make the ES lasing devices, especially InAs/InP ones emitting at 1.55 μm, more attractive for direct modulation in high-speed optical communication systems. [ABSTRACT FROM AUTHOR]

In this paper, the gain, phase, and refractive index dynamics of photonic crystal quantum-dot semiconductor optical amplifiers (PC-QDSOAs) are investigated for the first time. For this purpose, we establish a comprehensive nonlinear state space model with 1088 state variables to simulate the carrier dynamics of the inhomogeneously broadened InAs/GaAs QD active region embedded in a flat-band slow-light photonic crystal waveguide. The gain and phase recovery responses are monitored during the amplification of an ultrashort pump pulse. Simulation results show that changes in refractive index in the PC-QDSOA active region are much stronger than the index changes in the conventional QDSOAs. In addition, the gain and phase recovery time in PC-QDSOAs are similar to those in the conventional QDSOAs based on ridge waveguide structures. Also, we found that the injected current and the consumed power in PC-QDSOAs can be two orders of magnitude less than those values in the conventional QDSOAs. [ABSTRACT FROM AUTHOR]

In this letter, we propose a new design for a multicolor InAs/GaAs quantum dot (QD) infrared photodetector based on metallic nanoslits array. The proposed device has an absorption coefficient of more than 50% for designed wavelengths in the infrared (IR) range. We analyze the absorption characteristics of the InAs/GaAs QDs affected by metallic nanoslits. Distributed Bragg reflector layers with a buried grating layer are used for enhancement of local field in active layer. The dielectric function of the InAs/GaAs QD layer is calculated by modified Maxwell-Garnett model considering homogeneous and inhomogeneous broadenings, which is then substituted into Maxwell's equations. Results show absorption enhancement of ~100% for certain wavelengths in the IR range, compared with reference structure. [ABSTRACT FROM PUBLISHER]

We discuss relevant design considerations for the fabrication of electromechanically tunable photonic crystal cavities based on double semiconductor slabs. A simple optical and electromechanical model of the device based on coupled-mode theory and electrostatics is discussed and used jointly with 3-D finite-element calculations of optical cavity modes to extract the tuning-range dependence on geometrical parameters. A design rule, which avoids the sticking of membranes due to capillary forces and keeps a large tunability, is defined. The details of the fabrication process and a summary of the experimental results on GaAs and InGaAsP/InP material systems are given. We also address the problem of nonsymmetric devices, where the thicknesses of the membranes are not exactly the same, resulting in an imbalanced power emission of coupled modes. [ABSTRACT FROM AUTHOR]

We have investigated the dislocation filtering characteristics of InGaN/GaN quantum dot multilayers grown at the substrate/active layer interface along the c-axis. Etch pit dislocation density measurements reveal a reduction in defect density by a factor of 5, from ~ 5×108 cm-2 to ~ 9.8×107 cm-2 in a GaN overlayer with an optimized quantum dot multilayer. This is accompanied by a reduction of electron and hole trap densities in the GaN layer by a factor of 3 and an increase in the luminescence efficiency of green-emitting In0.35Ga0.65N/GaN quantum dots grown atop such filters. Green-emitting (λ = 525 nm) quantum dot light emitting diodes having optimized dislocation filter show marked improvement in their current-voltage and light-current characteristics and in their external quantum efficiency. The peak efficiency is achieved at an injection level of 27 A/cm2. [ABSTRACT FROM PUBLISHER]

The ideal diode approximation is used to evaluate the properties of many semiconductor diode-based devices. However, when it is applied to lasers and photovoltaics, which incorporate quantum dots (QDs), the ideality factors measured are difficult to interpret. Here, we show that a proper consideration of carrier escape from the QD confined states overcomes this problem. In addition, this approach suggests a novel method of empirically estimating the absolute value of the escape current at the threshold current of a laser diode. We argue that this technique will be of great importance in the experimental analysis of nonradiative losses in lasers and should also prove useful to the development of next-generation QD photovoltaics where thermal carrier escape must be minimized. [ABSTRACT FROM PUBLISHER]

The performance improvements of adding InAs quantum dots (QDs) in the middle subcell of a lattice matched triple-junction InGaP/InGaAs/Ge photovoltaic device are studied using the simulated external quantum efficiency, photocurrent, open circuit voltage, fill factor, and efficiency under standard testing conditions. The QDs and wetting layer are modeled using an effective medium consisting of trap states for the former and low confinement potentials for the latter. Although the efficiency stabilizes for more than 100 layers of QDs for the structure studied, the efficiency achieves an absolute efficiency of 31.1% under one sun illumination for 140 layers of QDs. This corresponds to a relative increase of 1.3% compared with a control structure with no QD layers. The performance of the device depends intricately on the magnitude of the confinement potentials representing the wetting layer. [ABSTRACT FROM PUBLISHER]

We realized two PbS colloidal quantum dot (CQD) based Schottky photodetectors, formed of indium tin oxide anode, the photosensitive PbS layer, and a Schottky contacts of titanium-gold (Ti-Au) stack for higher longer lifetime and aluminum (Al) for higher responsivity. Long capping ligands of PbS QDs were replaced with shorter ones and layer-by-layer deposition method was applied to form pinhole-free and uniform PbS CQD films, enabling better responsivity and longer lifetime. In Al/PbS, under 2 V reverse bias and 5 mW/cm2 illumination at 1550 nm, 0.195 A/W responsivity, 15.6% quantum efficiency, and 8.19 ×1010 Jones normalized detectivity is achieved. In Au-Ti/PbS, under 3 V reverse bias and 5 mW/cm2 illumination, 0.667 A/W responsivity, 53.3% quantum efficiency, and 2.12 ×1010 Jones normalized detectivity is achieved. [ABSTRACT FROM PUBLISHER]

We deposited a p-i-n structure device with alternative amorphous Si (a-Si) and amorphous SiC (a-SiC) multilayers as an intrinsic layer in a plasma-enhanced chemical vapor deposition (PECVD) system. A KrF pulsed excimer laser-induced crystallization of a-Si/a-SiC stacked structures was used to prepare Si quantum dots (Si QDs)/SiC multilayers. The formation of Si QDs with an average size of 4 nm was confirmed by Raman spectra, whereas the layered structures were revealed by cross-sectional transmission electron microscopy. Electroluminescence (EL) devices containing Si QDs/SiC multilayers embedded in a p-n junction were fabricated, and the device performance was studied and compared with the reference device without the p-i-n structure. It was found that the turn-on voltage was reduced and that luminescence efficiency was significantly enhanced by using the p-i-n device structure. The recombination mechanism of carriers in a Si-QD-based EL device was also discussed, and the improved device performance can be attributed to the enhanced radiative recombination probability in a p-i-n EL device. [ABSTRACT FROM PUBLISHER]

We have used ferromagnetic resonance (FMR) at fixed frequency 9.7 GHz to investigate permalloy thin films patterned with antidots to form a five-fold quasicrystal pattern. For DC applied fields H below 3.5 kOe, we observed robust FMR spectra exhibiting two-fold rotational symmetry instead of the five-fold symmetry expected for quasicrystals. Dynamic micromagnetic simulations of the FMR spectra performed at H=1\ kOe and 12 kOe exhibit two-fold and ten-fold rotational symmetry, respectively. The ten-fold symmetry observed in simulations is consistent with a saturated state of isolated write fields. We infer the two-fold rotational symmetry observed for H=1\ kOe is due to an unsaturated state of five-fold write fields closely spaced on a square lattice. [ABSTRACT FROM AUTHOR]

Bright single-photon emission from single quantum dots (QDs) in suspended circular Bragg grating microcavities is demonstrated. This geometry has been designed to achieve efficient (>\!50\%) single-photon extraction into a near-Gaussian-shaped far-field pattern, modest (\approx 10 \times) Purcell enhancement of the radiative rate, and a spectral bandwidth of a few nanometers. Measurements of fabricated devices show progress toward these goals, with collection efficiencies as high as \approx\!10\% demonstrated with moderate spectral bandwidth and rate enhancement. Photon correlation measurements are performed under above-bandgap excitation (pump wavelength = 780 to 820 nm) and confirm the single-photon character of the collected emission. While the measured sources are all antibunched and dominantly composed of single photons, the multiphoton probability varies significantly. Devices exhibiting tradeoffs among collection efficiency, Purcell enhancement, and multiphoton probability are explored and the results are interpreted with the help of finite-difference time-domain simulations. Below-bandgap excitation resonant with higher states of the QD and/or cavity (pump wavelength = 860 to 900 nm) shows a near-complete suppression of multiphoton events and may circumvent some of the aforementioned tradeoffs. [ABSTRACT FROM PUBLISHER]

In this paper, the acceleration of phase recovery in quantum-dot semiconductor optical amplifiers (QD-SOAs) is investigated by employing optical pumping (OP) scheme. For this purpose, the state space theory has been used to derive a dynamic model for the QD-SOA. The derived nonlinear state space model is employed to simulate the gain and phase responses of the device. For the first time, we show that OP can realize a shorter phase recovery time in comparison with electrical pumping (EP) scheme under equal pumping powers. We found that under OP, the contribution of slow phase recovery component induced by the slow carrier dynamics of the carrier reservoir is drastically reduced, and consequently, a fast phase response becomes feasible. Also, we found that under EP, the gain is recovered within a shorter time compared to OP scheme. [ABSTRACT FROM PUBLISHER]

This paper reviews recent progress in nanophotonics, a novel optical technology proposed by one of the authors (M. Ohtsu). Nanophotonics utilizes the local interaction between nanometric particles via optical near fields. The optical near fields are the elementary surface excitations on nanometric particles, that is, dressed photons that carry the material energy. Of the variety of qualitative innovations in optical technology realized by nanophotonics, this paper focuses on devices and systems. The principles of device operation are reviewed considering the excitation energy transfer via the optical near-field interaction and subsequent dissipation. As representative examples, the principles of a nanophotonic and gate, not gate, and optical nanofountain are described. Experimental results for operating devices using CuCl quantum dots (QDs), InAlAs QDs, and nanorod ZnO double quantum wells are described. Using a systems-perspective approach, the principles of content-addressable memory based on nanophotonic device operations and experimental results are reviewed. The hierarchy of optical near-field interactions is discussed, and its application to a multilayer memory retrieval system is demonstrated. [ABSTRACT FROM PUBLISHER]

This paper reports on integration of two silicon (Si) charge quantum bits (qubits) and series-connected double single-electron transistors (DSETs) as readout for the first time. We design and fabricate the DSETs composed of double quantum dots (DQDs) connected in series with two side gates patterned on a silicon-on-insulator substrate. The individual SETs are sufficiently sensitive to detect single-charge polarization on the adjacent charge qubits. The fabricated DSETs are characterized at a temperature of 4.2 K by changing the gate voltages applied to the two side gates. The measured Coulomb oscillation characteristics exhibit a clearly defined hexagon pattern, manifesting that the patterned DQDs of the DSETs, indeed, act as interacting charging islands. These results agree very well with the results of equivalent circuit simulation combined with 3-D capacitance simulation. Furthermore, we simulate how single-charge configurations on two charge qubits are sensed with the DSETs by using the measured electrical characteristics for the DSET and the equivalent model. Finally, the scaling-up properties of the proposed system to multiple single-electron transistors (MSETs) are discussed by simulating triple single-electron transistors (TSETs) with triple qubits. [ABSTRACT FROM PUBLISHER]

The multicolor absorption of MOS SiGe/Si quantum-dot (QD) infrared photodetectors is demonstrated using the boron delta-doping in Si spacers. The energy-dispersive X-ray spectroscopy shows that the Ge concentration in the wetting layers is much smaller than that in QDs. Most holes stay at the ground state in QDs instead of wetting layers. The energy band structure in QDs is calculated to understand the absorption spectrum. The absorption at 3.7-6 mum is due to the intersubband transition in the SiGe QDs. The other absorption at 6-16 mu m mainly comes from the intraband transition in the boron delta-doping wells. Since the broadband spectrum covers most of the atmospheric transmission windows for infrared, the broadband detection is feasible using this device. [ABSTRACT FROM PUBLISHER]

In this paper, we study an unconventional kind of quasi-three-dimensional (3-D) photonic crystal (PhC) with circular lattice pattern: it consists of air holes in a GaAs material (n=3.408) along circular concentric lines. This particular PhC geometry has peculiar behavior if compared with the traditional square and triangular lattices, but it is difficult to model by using conventional numerical approaches such as wave expansion method. The resonance and the radiation aspects are analyzed by the 3-D finite-element method (FEM). The model, based on a scattering matrix approach, considers the cavity resonance frequency and evaluates the input-output relationship by enclosing the photonic crystal slab (PhCS) in a black box in order to define the responses at different input-output ports. The scattering matrix method gives important information about the frequency responses of the passive 3-D crystal in the 3-D spatial domain. A high sensitivity of the scattering parameters to the variation of the geometrical imperfection is also observed. The model is completed by the quality factor (Q-factor) estimation. We fabricated the designed circular photonic crystal over a slab membrane waveguide embedding InAs/GaAs quantum dots emitting around 1.28 mum. Good agreement between numerical and experimental results was found, thus validating the 3-D FEM full-wave investigation. [ABSTRACT FROM PUBLISHER]

In this paper, the basics and some of the recent developments in quantum dots-in-a-well (DWELL) focal plane arrays (FPAs) are reviewed. Fundamentally, these detectors represent a hybrid between a conventional quantum well infrared photodetector (QWIP) and a quantum dot infrared photodetector (QDIP), in which the active region consists of quantum dots (QDs) embedded in a quantum well (QW). This hybridization grants DWELLs many of the advantages of its components. These advantages include normally incident photon sensitivity without gratings or optocoupers, like QDIPs, and reproducible control over operating wavelength through ldquodial-in recipesrdquo as seen in QWIPs. Recently reported high-temperature operation results for DWELL FPAs now back up the conclusions drawn by the long carrier lifetimes observed in DWELL heterostructures using femtosecond spectroscopy. This paper will conclude with a preview of some upcoming advances in the field of DWELL FPAs. [ABSTRACT FROM PUBLISHER]

Lateral ordering, position, and number control of self-organized epitaxial semiconductor quantum dots (QDs) are demonstrated. Straight linear InAs QD arrays are formed by self- organized anisotropic strain engineering of an InGaAsP/InP (10 0) superlattice template in chemical beam epitaxy. The QD emission wavelength at room temperature is tuned into the important 1.55 mum telecom wavelength region through the insertion of ultrathin GaAs interlayers. Guided self-organized anisotropic strain engineering is demonstrated on shallow- and deep-patterned GaAs (3 1 1)B substrates by molecular beam epitaxy for the formation of complex InGaAs QD arrays. Lateral positioning and number control of InAs QDs, down to a single QD, are demonstrated on truncated InP (100) pyramids by selective-area metal-organic vapor phase epitaxy. Sharp emission around 1.55 mum is observed well above liquid nitrogen temperatures. The regrowth of a passive waveguide structure establishes submicrometer-scale active- passive integration. The demonstrated control over QD formation is the key to future functional nanophotonic devices and paves the way toward the ultimates of photonic-integrated circuits operating at the single and multiple electron and photon level with control of the quantum mechanical and electromagnetic interactions. [ABSTRACT FROM PUBLISHER]

A growth technique for wide emission wavelength quantum dots (QDs) via the Stranski-Krastanov (S-K) growth mode using a double-cap procedure and metal-organic vapor phase epitaxy (MOVPE) selective area growth is proposed. By using the double-cap procedure, we have improved the uniformity of the QDs height. Selective area growth by low-pressure MOVPE using a SiO2 narrow stripe mask array pattern was carried for controlling and widening the emission wavelength range of the QDs in 16 stripe mask array waveguides. We have successfully demonstrated QD characteristics under various growth conditions, and have realized 120 nm emission wavelength range in 16 array, five layer InAs QD waveguides. [ABSTRACT FROM PUBLISHER]

We have demonstrated the fabrication and characterization of hybrid CdSe/ZnS quantum dot (QD)–InGaN blue LEDs. The chemically synthesized red light (lambda = 623 nm) QD solutions with different concentrations were dropped onto the blue InGaN LEDs with an emission peak of 453 nm and the turn-on voltage of 2.6 V. In this configuration, the CdSe/ZnS core/shell QDs played the role of a color-conversion center. It was clearly observed that the emission intensity from QDs was increased with increasing QD concentration. With a QD concentration of 10 mg/ml in toluene was incorporated, the ratio of emission intensity of QDs to that of InGaN quantum wells reached 0.17, whereas the Commission Internationale de l’Eclairage (CIE) chromaticity coordinates greatly shifted to (0.29, 0.14). From the spatial mapping of electroluminescence spectra, the decrease of the intensity of EQW seems to be faster than that of EQD, which suggests that the QD film thickness may be thicker in the edge of the surface of InGaN chip. There will, therefore, convert higher proportion of blue light to red light. Also, the resin-encapsulated hybrid LEDs have a divergence angle (the full angle at 1/e^2 intensity) of about 20^circ as the device is operated at 10 mA. Furthermore, under the injection current of 20 mA and room temperature, this device can be operated for more than 1000 h without any obvious degradation. From our results, it can be proven that the synthesized QDs are promising nanophosphors for color-conversion applications of solid-state LEDs. However, to more efficiently convert the blue light to red light, a denser QD solution with higher quantum yield must be utilized. [ABSTRACT FROM PUBLISHER]

A nonvolatile memory is explored theoretically by utilizing the magnetic exchange interaction between localized holes and an adjacent ferromagnetic (FM) material. The active device consists of a buried semiconductor quantum dot (QD) and an FM insulating layer that share an interface. The hole population in the QD is controlled by particle transfer with a reservoir of itinerant holes over a permeable barrier. A theoretical model based on the free energy calculation demonstrates the existence of a bistable state through the mechanism of a collective spin polaron, whose formation and dissolution can be manipulated electrically via a gate bias pulse. The parameter space window suitable for bistability is examined along with the conditions that support maximum nonvolatility. The limitation of QD size scaling is analyzed in terms of the bit retention time. [ABSTRACT FROM PUBLISHER]

Selective postgrowth band gap tuning of self-assembled InAs/InGaAs/InP quantum dot (QD) structures has been investigated. Very large band gap blueshift of over 158 meV of the InAs QD structure has been received through the intermixing by exposing the sample under argon plasma and followed by thermal annealing at 780 °C. Selective intermixing of the InAs QD structure has been studied by depositing a SiO2 mask layer on the sample for the intermixing. The largest selective band gap shift between the SiO2 covered and uncovered regions of the sample reaches 77 meV. This intermixing selectivity decreases when the annealing temperature is increased. This reduction in the intermixing selectivity is attributed to the enhanced QDs intermixing of the SiO2-masked samples because of the out diffusion of different elements from the InAs/InGaAs/InP QD structure into the SiO2 cover layer. Three different energy band gap shifts of an InAs/InGaAs/InP QD structure across the wafer have been received by this postgrowth selective intermixing. The selective band gap tuning paves a way for monolithic integration of passive and active optoelectronic devices in QD systems. [ABSTRACT FROM PUBLISHER]

We report time-resolved measurements of the linewidth enhancement factors (-factors) , and , associated with the adiabatic carrier recovery, carrier heating, and two-photon absorption dynamical processes, respectively, in semiconductor optical amplifiers (SOAs) with different degrees of dimensionality-one InAs/InGaAsP/InP quantum dot (0-D), one InAs/InAlGaAs/InP quantum dash (1-D), and a matching InGaAsP/InGaAsP/InP quantum well (2-D)-all operating near 1.55- wavelengths. We find the lowest values in the QD SOA, 2-10, compared to 8-16 in the QW, and values of and that are also lower than in the QW. In the QD SOA, the -factors exhibit little wavelength dependence over the gain bandwidth, promising for wide-bandwidth all-optical applications. We also find significant differences in the -factors of lasers with the same structure, due to the differences between gain changes that are induced optically or through the electrical bias. For the lasers we find the QW structure instead has the lower -factor, having implications for directly modulated laser applications. [ABSTRACT FROM PUBLISHER]

Doped with PbSe nanocrystals of different sizes, a multiquantum-dot-doped fiber amplifier (MQDFA) is proposed. Performance of the MQDFA is simulated by solving light-propagation equations and rate equations for a three-level system, and by applying superposed emission-absorption cross sections of the quantum dots (QDs). Pumped with 980 nm, this proposed MQDFA has characteristics of broader band, flatter gain, and lower noise than those of the erbium-doped fiber amplifiers at present. There is evidence to show that two factors, i.e., the equivalent Stokes shifts and the full wave at half maximum of the superposed spectra, dominate the performances of the MQDFA. Also, the equivalent Stokes shift and the FWHM are tunable by adopting the QDs in different sizes and choosing the doped number available. It is expected that such a MQDFA may be able to cover the all waveband in telecommunications if it is optimized on the doped number, sizes, and doped concentrations of the QDs. [ABSTRACT FROM PUBLISHER]

We report a room temperature operating InAs quantum-dot infrared photodetector grown on InP substrate. The self-assembled InAs quantum dots and the device structure were grown by low-pressure metalorganic chemical vapor depositon. The detectivity was 6 times 1010 cm Hz1/2/W at 150 K and a bias of 5 V with a peak detection wavelength around 4.0 mum and a quantum efficiency of 48%. Due to the low dark current and high responsivity, a clear photoresponse has been observed at room temperature. A 320 times 256 middle wavelength infrared focal plane array operating at temperatures up to 200 K was also demonstrated. The focal plane array had 34 mA/W responsivity, 1.1% conversion efficiency, and noise equivalent temperature difference of 344 mK at 120 K operating temperature. [ABSTRACT FROM PUBLISHER]

In this paper, we analyze vibration-assisted sequential tunneling (including current-voltage characteristics and zero-frequency shot noise) through a molecular quantum dot with two electronic orbitals asymmetrically coupled to the internal vibration. We employ rate equations for the case of equilibrated phonons, and strong Coulomb blockade. We find that a system with a strongly phonon-coupled ground state orbital and weakly phonon-coupled excited state orbital exhibits strong negative differential conductance; and it also shows super-Poissonian current noise. We discuss in detail the reasons and conditions for the appearance of negative differential conductance. [ABSTRACT FROM PUBLISHER]

Novel fluorescent silkworm silks incorporated with CdTe quantum dots (QDs) have been prepared via electrostatic assembly using a polyelectrolyte (PE) as a fixer. The bright fluorescence of the silks/QDs obtained could be tuned from green to near-infrared (NIR) by changing the QD size, thereby enabling the fluorescence to penetrate through an opaque pig skin of ~3.5 mm in thickness. A large amount of the QDs were not only deposited on the surface of the silk, but also found permeated into the silk. The silk incorporated with just one PE/QDs/PE layer exhibited a smooth surface. However, the presence of more PE/QDs/PE layers in the silk resulted in an increased surface roughness. The mechanical properties of the silks incorporated with one PE/QDs/PE layer were close to those of pure silks, but the maximum pull force and elastic limit elongation at break of a single silk thread decreased with increasing number of PE/QDs/PE layers. Although a very small amount of Cd2+ and Te2- ions were released from the silks/QDs in neutral and alkaline aqueous solutions, nearly no QD were released from these fluorescent silks. The fluorescence intensity of the silk/QDs was stable in neutral and alkaline aqueous solutions, but significantly decreased in acidic solution. The simple preparation method of the silks/QDs reported in this paper is both highly efficient and low cost, and the fluorescent silks obtained are anticipated to be of great interest for fabricating multicolored fluorescent cloths and anticounterfeiting labels, as well as being useful for other bio- or physico-related applications. [ABSTRACT FROM PUBLISHER]

We report the optical characteristics and the linewidth enhancement factor (alpha-factor) of InAs/GaAs quantum dot (QD) laser diodes (LDs) with a 5-mum-wide stripe and 1-mm-long cavity. Continuous wave (CW) operation of the laser yielded a kink-free output power of 160 mW with an external efficiency of 0.35 W/A. The threshold current was 28 mA and the lasing occurred at 1286 nm, solely at the ground state (GS) up to a current of 345 mA, without switching to the excited state (ES). Then, to estimate the alpha-factor of the LDs, we investigated the differential gain and wavelength shift versus the current. The differential gain was 2.37 cm-1/mA at 1286 nm, and the wavelength shift was 0.00046 nm/mA, which resulted in an alpha-factor of 0.057 at 1286 nm. The alpha-factor decreased with increasing wavelength. To the best of our knowledge, this is the lowest value of the alpha-factor that has been reported so far, indicating that our QD-LD has excellent beam quality under high-power operation due to the elimination of the filamentation. [ABSTRACT FROM PUBLISHER]

We demonstrate the first reported use of single-walled carbon nanotubes as nano-optical probes in apertureless near-field fluorescence microscopy. We show that, in contrast to silicon probes, carbon nanotubes always cause strong fluorescence quenching when used to image dye-doped polystyrene spheres and Cd-Se quantum dots. For quantum dots, the carbon nanotubes induce very strong near-field contrast with a spatial resolution of 20 nm. Images of dye-doped spheres exhibit crescent-shaped artifacts caused by distortions in the surface water layer found in ambient conditions. [ABSTRACT FROM PUBLISHER]

In this paper we report on a general methodology to investigate nanowire MOSFETs based on the coupling of mechanical simulation with 3-D real-space Monte Carlo simulation. The Monte Carlo transport model accounts for both strain silicon and quantum mechanical effects. Mechanical strain effects are accounted for through an appropriate change of the anisotropic band structure computed with the empirical pseudopotential method. Quantum effects are instead included by means of a quantum mechanical correction of the potential coming from the self-consistent solution of the Schrodinger equation. This methodology has been then applied to the simulation of a test case silicon nanowire n-MOSFET. Impact of mechanical strain and quantum effects on the drive current is investigated. It is shown that only the inclusion of strain and quantum mechanical effects allows a good agreement with experimental data, demonstrating the validity of the proposed methodology for ultimate devices. [ABSTRACT FROM PUBLISHER]

In this paper, we report that low-density InAs/GaAs quantum dots (QDs) can be formed by postgrowth annealing the samples with 1.5-monolayer (ML) InAs coverage, which is thinner than the critical layer thickness for the Stranski-Krastanov growth. The annealing procedure was performed immediately after the deposition of the InAs layer. The effects of annealing time and annealing temperature on the dot density, dot size, and optical characteristics of the QDs were investigated. The optimum annealing conditions to obtain low-density QDs are longer than 60 s and higher than 500degC . Meanwhile, no luminescence can be observed for the wetting-layer, which may suggest that the postgrowth annealing will make the wetting layer thinner and thus reduce the effects of wetting layer on carrier relaxation and recombination. On the other hand, we observe that a decrease of the PL intensity at the annealing conditions of 60 s and 515degC , which is possibly due to the increasing surface dislocations resulted from the In adatom desorption at higher annealing temperature. [ABSTRACT FROM PUBLISHER]

Quantum dot (QD) superluminescent diodes (SLDs) exhibiting 8 mW and 95 nm full-width at half-maximum centered at 1270 nm are demonstrated with a flat-topped spectral profile. This is achieved using 3 times 2 dots in compositionally modulated wells technique. Furthermore, techniques for realization of high-power SLDs are also demonstrated. A continuous-wave output power of 42 mW is achieved for narrowband devices centered at 1250 nm. [ABSTRACT FROM PUBLISHER]

We have reported the effects of using an As2 source and gradient composition-strain reducing laser (GC-SRL) to fabricate InAs quantum dot (QD) structures. The coalescence of the coherent QDs was reduced under the As2 source. We have realized high density (8.0 times1010 cm-2 per sheet) measured by SEM and high uniformity (full-width at half-maximum: 23 meV measured by photoluminescence at room temperature) QDs using an As2 source and the GC-SRL technique. Further, we have demonstrated nine- stack QD lasers with high-density and high-uniformity QDs for the first time. We achieved a large modal gain of 54 cm-1 at a ground state emission of beyond 1.3-mum. A very low threshold current can be realized by a quantum effect for further equalization of QDs. We believe that the method of fabricating this QD laser with high density, high uniformity, and high modal gain will qualify as a novel technique. [ABSTRACT FROM PUBLISHER]

In this study we investigated the effects that the carrier dynamics have on the temperature- and excitation-intensity- dependent photoluminescence (PL) spectra of a self-assembled quantum dot heterostructure. A rate equation model is proposed to take into account the dot size distribution, the random population of density of states, state filling effects, and the important carrier transfer mechanisms for the quantum dot system, including carrier capture, relaxation, thermal emission, and retrapping. This model reproduces the PL spectra quite well. Our quantitative calculations of the behavior of the thermal emitting carriers under various incident power intensities within the temperature range 15 K-240 K explain the carrier transfer process quite reasonably for the quantum dot system. In addition, we discuss the thermal redistribution and state filling effects in detail in our analysis of the dependence of the PL spectra on the temperature and excitation power intensity applied to the sample. Index [ABSTRACT FROM PUBLISHER]

We report on the operation of a novel single-photon detector, where a layer of self-assembled quantum dots (QDs) is used as an optically addressable floating gate in a GaAs/Al0.2Ga0.8As delta-doped field-effect transistor. Photogenerated holes charge the QDs, and subsequently, change the amount of current flowing through the channel by screening the internal gate field. The photoconductive gain associated with this process makes the structure extremely sensitive to light of the appropriate wavelength. We investigate the charge storage and resulting persistent photoconductivity by performing time-resolved measurements of the channel current and of the photoluminescence emitted from the QDs under laser illumination. In addition, we characterize the response of the detector, and investigate sources of photogenerated signals by using the Poisson statistics of laser light. The device exhibits time-gated, single-shot, single-photon sensitivity at a temperature of 4 K. It also exhibits a linear response, and detects photons absorbed in its dedicated absorption layer with an internal quantum efficiency (IQE) of up to (68 plusmn18)%. Given the noise of the detection system, the device is shown to operate with an IQE of (53 plusmn 11)% and dark counts of 0.003 counts per shot for a particular discriminator level. [ABSTRACT FROM PUBLISHER]

We describe the design and characterization of a fiber-coupled double-channel single-photon detection system based on superconducting single-photon detectors (SSPD), and its application for quantum optics experiments on semiconductor nanostructures. When operated at 2-K temperature, the system shows 10% quantum efficiency at 1.3-mum wavelength with dark count rate below 10 counts per second and timing resolution <100 ps. The short recovery time and absence of afterpulsing leads to counting frequencies as high as 40 MHz. Moreover, the low dark count rate allows operation in continuous mode (without gating). These characteristics are very attractive-as compared to InGaAs avalanche photodiodes-for quantum optics experiments at telecommunication wavelengths. We demonstrate the use of the system in time-correlated fluorescence spectroscopy of quantum wells and in the measurement of the intensity correlation function of light emitted by semiconductor quantum dots at 1300 nm. [ABSTRACT FROM PUBLISHER]

The detailed study of the effects of spin recipe and GaAs substrate doping (i.e., semi-insulating, n-type, or p-type) on the structural and optical properties of spin-cast CdSe-CdS core-shell CQDs provides insight into the surface adsorption and charge transfer mechanisms that will influence any potential optoelectronic device. The hypotheses of this study are: i) it is possible to establish spin-casting recipes that yield a thin film of CQDs with large surface density and uniform size, and ii) it is possible to control the optical response of CQDs by varying the GaAs substrate doping to influence charge transfer processes. As a result of these measurements, we have been able to demonstrate a strong dependence of spin-cast CQD structural properties on the doping type of the GaAs substrate, as well as evidence from measured optical properties to support the idea that hot carriers photoexcited in the GaAs substrate are transferred either to the CQD surface states through organic surface ligands or directly to confined states within the CQD. [ABSTRACT FROM PUBLISHER]

Recent progress in transition metal (TM)-doped II-VI semiconductor materials (mainly Cr2+:ZnSe) makes them the sources of choice for laser when one needs a compact continuous wave (CW) system with tunability over 1.9-3.1 mum, output powers up to 2.7 W, and high (up to 70%) conversion efficiency. The unique combination of technological (low-cost ceramic material) and spectroscopic characteristics make these materials ideal candidates for new regimes of operation such as microchip and multiline lasing. This paper reviews these nontraditional Cr-doped middle-infrared (mid-IR) lasers as well as describes emerging Fe2+:ZnSe lasers having potential to operate at room temperature (RT) over the spectral range extended to 3.7-5.1 mum. In addition to being wideband semiconductors, effective RT mid-IR lasing TM-doped II-VI media also hold potential for direct electrical excitation. This paper shows the initial steps toward achieving this goal by studying Cr2+-Co2+- and-doped quantum dots. We have demonstrated a novel method of TM-doped II-VI quantum dots fabrication based on laser ablation in liquid environment. TM-doped II-VI quantum dots demonstrated strong mid-IR luminescence. It opens a new pathway for future optically and electrically pumped mid-IR lasers based on TM-doped quantum confined structures. [ABSTRACT FROM PUBLISHER]

For the future development of semiconductor quantum dot transistors, a novel n-i-p-type semiconductor quantum dot transistor consisting of an n-type source, an i-type dot, and a p-type drain is presented in this paper. The explicit steady-state solution to a set of an infinite number of stochastic theoretical probability equations is given. The solution is applicable to both metal and semiconductor quantum dot transistors. The electron and hole current characteristics controlled by means of the gate voltage are computed numerically, and it is pointed out that the electron or hole current state can be selected by applying a positive or negative gate voltage [ABSTRACT FROM PUBLISHER]