InP-based Quantum Dots Research Articles

Quantum Dots based on Indium Phosphide (InP): the Effect of Chemical Modifications of the Organic Shell on Interaction with Cultured Cells of Various Origins

CdSe and CdTe-based semiconductor fluorescent nanocrystals, also called quantum dots (QDs), attract the attention of biologists due to their wide range of emission in a visible light interval, high fluorescence quantum yield and photostability. However, their application is limited because of possible toxicity of cadmium. Indeed, there is a probability of metal leakage from QDs cores as a result of damage of both inorganic and organic layers of shells covering QDs. An alternative to cadmium QDs could be nanostructures having as a core, for example, non-toxical indium phosphide (InP), also emitting in the visible region of the spectrum. At present, there is few works on the use of these particles in biology. In this study, a comparative analysis of the spectral-luminescent properties of two InP/ZnS-QDs samples coated with PEG carrying- COOH or -NH2 functional groups was performed. The obtained data were compared with the characteristics of CdSe/ZnS-QDs coated with PEG. The photophysical properties of all QDs in aqueous solution corresponded to the information claimed by manufacturers, but the fluorescence quantum yield of InP-based nanoparticles was found to be lower than that of CdSe-QDs. We also show that the photoluminescence of all types of QDs at pH 4.0 was lower than at pH 7.4, while the decrease in fluorescence intensity was minimal in the case of QDs-PEG-COOH. Studying the uptake of all three types of QDs by J774 macrophages, we found that the fluorescence spectra of internalized QDs do not change in comparison with those in solution. All three types of QDs after 24 hours of incubation were accumulated in the cells, but while QDs-NH2 and QDs without reactive groups were detected mainly in vesicular-like discrete structures, the QDs-COOH were diffusely distributed throughout the cytoplasm. This fact indicates different mechanisms of interaction with cell membranes. In nonphagocytic HeLa cells all types of QDs behaved similarly, but the overall level of cells fluorescence was much lower. This may be due to both reduced nonspecific uptake and possible quenching of QDs fluorescence in acidic endolysosomes. Cytofluorimetric analysis of propidium iodide accumulation showed that after 24 hours incubation with all studied types of QDs as well as in control (no QDs), the proportion of dead HeLa cells did not exceed 10%. Thus, it has been demonstrated that non-toxic InP-based QDs can be used as an effective tool for biological research.

Enhanced luminescence efficiency of wet chemical route synthesized InP-based quantum dots by a novel method: Probing the humidity sensing properties

In indium phosphide quantum dots (InP QDs), the presence of surface states due to unbonded indium or phosphorus atoms quenches its photoluminescence (PL) efficiencies. Hence, it is imperative to passivate these surface states to achieve high photoluminescence efficiencies of InP nanocrystals. In this work, a novel post-synthesis nascent H chemical treatment to enhance the quantum yield of single-pot, wet chemical route synthesized InP QD's is reported for the first time. The main advantages of this post-synthesis treatment are: (i) it is easy, inexpensive and reproducible and (ii) it does not involve harsh chemical treatment viz. dipping of InP QDs in HF-based solutions, nor it requires annealing at high temperatures which may be detrimental to the fragile structure of InP. The significant increment in PL intensity upon aforementioned hydrogen treatment is due to the passivation of surface states and structural recrystallization mechanism that promotes radiative recombination of electrons and holes and hence higher lifetime values. An enhancement in PL intensity of as-synthesized InP QDs upon nascent hydrogen treatment is quite remarkable and is even better than that accomplished by InP-ZnS core-shell QDs with similar size-distribution. The hydrophobicity of H-treated InP QD's is found to be more than untreated InP thus implying higher compactness and structural rigidity similar to as achieved by InP-ZnS core-shell QDs. Mechanisms related to nascent hydrogen treatment, photo-oxidation and PL enhancement and its effect on the surface stoichiometry of InP QDs are discussed via structural, morphological, compositional and optical studies corroborated by various complementary techniques viz. SEM, HRTEM, EDAX,NMR, DLS, Zeta Potential, Contact Angle, PL and Transient Absorption respectively. The application of InP films as a humidity sensor has been demonstrated and untreated InP film in particular shows higher sensitivity values upon exposure to humid treatment as compared with H-treated InP and InP-ZnS core-shell QD's respectively.

Highly Photoluminescent InP Based Core Alloy Shell QDs from Air-Stable Precursors: Excitation Wavelength Dependent Photoluminescence Quantum Yield, Photoluminescence Decay Dynamics, and Single Particle Blinking Dynamics

InP based quantum dots (QDs) are coming in a big way as an alternative to toxic Cd, or Pb based QDs. Unlike many literature reports in this work, green-yellow-orange-red emitting highly photoluminescent (PLQY as high as 65%) and photostable InP/ZnSeS core/alloy shell quantum dots (CAS QDs) have been synthesized using a less toxic, air-stable aminophosphine precursor (P(DMA)3). Unlike literature predictions in this paper, we show that green-yellow-orange-red emitting InP based alloyed QDs can be prepared with InCl3 only. We report here the hitherto unobserved and quite interesting excitation wavelength dependent PLQY for all of these green-yellow-orange-red emitting InP based CAS QDs. PLQY increases monotonically with increasing excitation wavelength. Significant deviation of the PL excitation spectrum from the absorption spectrum has been observed in the shorter wavelength region. This observation is perhaps because the surface mediated nonradiative pathways predominate over radiative charge carrier recom...

Flexible InP based quantum dot light-emitting diodes using Ag nanowire-colorless polyimide composite electrode

A smooth, flexible, and transparent electrode was fabricated by embedding a percolated network of Ag nanowires (AgNWs) at a surface of colorless polyimide utilizing an inverted layer film-processing approach. The electrode with buried AgNWs showed excellent physical characteristics: a smooth surface roughness (less than 1 nm in root-mean-square roughness), high flexibility (resisted cyclic bend testing with a curvature radius of 500 μm for 1000 iterations), high transparency (higher than 84% at a wavelength of 550 nm), and good conductivity (12.38 Ω/sq for sheet resistance). One demerit that remained for this electrode was a limited surface coverage of conductive pathways for electric carrier transference, originated from the fully embedded structural configuration. Here, the authors could successfully deal with this issue by an Ar plasma treatment in order to partially excavate the embedded AgNWs without a significant increase in surface roughness. Green quantum-dot light-emitting diodes (QLEDs) using InP based quantum dots were fabricated using these composites as a bottom electrode. Hole-injection was poor for an electrode without the plasma treatment since the AgNWs were fully buried beneath the composite's surface. As a result of the plasma treatment, however, the authors could obtain much improved electroluminescence properties of the flexible QLEDs due to the enlarged conductive pathways. The fabricated flexible devices showed durable performance even under a bending with a curvature radius of 5 mm.

Widely tunable narrow-linewidth 1.5 μm light source based on a monolithically integrated quantum dot laser array

A monolithically integrated widely tunable narrow-linewidth light source was realized on an InP-based quantum dot (QD) gain material. The quasi zero-dimensional nature of QDs and the resulting low linewidth enhancement factor enabled standalone distributed feedback (DFB) lasers with intrinsic linewidths as low as 110 kHz. An integrated device comprising four DFB lasers with on-chip micro-heaters, a 3 dB-coupler network, and a semiconductor optical amplifier (SOA), which covers the entire C+ telecom band, exhibits a linewidth of below 200 kHz independent of the SOA operation current.

Tapping the potential of trioctylphosphine (TOP) in the realization of highly luminescent blue-emitting colloidal indium phosphide (InP) quantum dots

In this work, extremely small blue emitting colloidal InP-based quantum dots (size ~ 2–5nm) have been synthesized using trioctylphosphine (TOP) as a source of phosphorus. The method reported here is unconventional, quite rapid (~90min), more viable, less expensive and relatively greener as compared to other conventional methods that employ tristrimethylsilyylphosphine(P(SiMe3)3) which is scarce, expensive, flammable, highly toxic and even banned in a few countries. Highly luminescent InP QDs having bluish-green emission (λ~ 490nm) can be synthesized using this method without resorting to any post-synthesis etching to tune the emission to the blue region. Besides being the source of phosphorus and the particle size regulating agent, the efficacy of TOP is further realized during synthesis via its reduction of indium salt, which aids in the formation of indium metal and then subsequently in the development of InP QDs. The PL intensity of as-synthesized InP QDs is further enhanced by growing a shell of wide band gap material, i.e. ZnS resulting in a concurrent increment in quantum yield from ~25% to ~38% respectively.

Efficient Förster Resonance Energy Transfer Donors of In(Zn)P/ZnS Quantum Dots

We demonstrate a detailed investigation of the effect of the type and concentration of zinc precursor on the optical properties of In(Zn)P/ZnS quantum dots. We achieved up to 87% quantum yield along with 54 nm emission bandwidth for the green emitters with changing the concentration of the Zn precursors. Employing efficient green emitters as the donor species, we demonstrated an efficient Förster resonance energy transfer (FRET) couple of green and red emitting InP-based quantum dots. With a FRET efficiency level of 70.3% achieved (analyzed from the donor lifetime with and without an acceptor), we further demonstrated the enhancement of the acceptor emission nearly twofold due to the energy transfer. Our results provide new insights toward the understanding of the excitonic interactions among donor and acceptor quantum dots of the III–V family for light harvesting applications.

InP/ZnSe/ZnS quantum dots with strong dual emissions: visible excitonic emission and near-infrared surface defect emission and their application in in vitro and in vivo bioimaging.

Quantum dots (QDs) exhibit many unique optical properties, and show great promise as fluorescent markers in molecular, cellular and in vivo imaging. In this thematic issue, a major concern is their cytotoxicity. Among various Cd-free alternatives, InP-based QDs without highly toxic heavy metal elements have received the most attention. This article first focuses on the synthetic control of oil-soluble InP/ZnSe/ZnS QDs, exhibiting strong dual emissions, namely, visible excitonic emission and near-infrared (NIR) surface defect emission. Next, the organic-to-aqueous phase transfer of the dual emissive QDs was explored systematically. It was found that the dual emissions are relatively stable against the water transfer strategies used here; among them, aqueous dual emissive QDs obtained by wrapping oil-soluble QDs with a poly(acrylic acid)-octylamine (PAA-based) amphiphilic polymer (or modified with the cRGD peptide) exhibit enhanced NIR emission. Finally, using in vitro cell and in vivo small animal optical imaging techniques, the bioactivities of the cRGD-modified amphiphilic polymer-wrapped QDs were also investigated. The results confirm that single-wavelength excitation with strong dual emissions ranging from 550 to >1000 nm will endow the InP-based QDs with the capability for biomedical optical imaging across different spatial scales, as a promising alternative for Cd- and Pb-based QDs.

Numerical characterization of InP-based quantum dot semiconductor optical amplifier.

This paper is devoted to the development of a steady-state behavior of a quantum dot-semiconductor optical amplifier (QD-SOA). The investigated performance characteristics cover a wide range that includes material gain coefficient, spatial distribution of the occupation probabilities, fiber to fiber gain, gain spectrum as a function of the bias current, relaxation time, and capture time. A set of traveling-wave equations is used to model the signal and spontaneous photons along the device active region. The obtained results indicate a high gain that reaches 34 dB for an InAs/InGaAsP/InP-based QD-SOA, with a corresponding device length of 4 mm. The obtained signal-to-noise ratio is larger than 75 dB for all input powers without using an output filter.

Surface Stabilized InP/GaP/ZnS Quantum Dots with Mg Ions for WLED Application.

One of the most highlighted cadmium-free quantum dots (QDs), InP-based QDs, have improved their optical properties. However, InP-based QDs have some practical drawbacks, for example, stability, compared with CdSe-based QDs. Poor stability of InP-based QDs yields critical problems, such as agglomeration and photoluminescence quenching in light emitting diode (LED). It has to be solved for applications and most research has focused on thick outer shells as an effective solution. We introduced magnesium cations for improving stability of InP-based QDs. We applied very small amounts of Mg cations as surface stabilizers, as a result, stability of QDs is clearly improved. Then, QD based LED chips also yield improved values including RA of 84.4, CCT of 3799 K, and luminous efficiency of 129.57 Im/W, which are highly improved data compared with our previous results.

Coherent photocurrent spectroscopy of single InP-based quantum dots in the telecom band at 1.5 µm

In this work we study the resonant and coherent properties of single InP-based InAs quantum dots, which show an optical emission in the telecom C-band and L-band. High-resolution resonant photocurrent spectroscopy on p–i–n devices reveals narrow linewidths and fully resolved fine structure splittings. We observe Lorentzian line shapes, which allow for the extraction of dephasing times as a function of the applied bias voltage. Coherent ps laser excitation results in pronounced Rabi rotations with increasing pulse area. For π-pulse excitation, we obtain more than 93 % of the theoretically expected photocurrent amplitude. Our results also demonstrate that such state-of-the-art InP-based quantum dots for the telecom band exhibit promising key parameters comparable to well-established InAs/GaAs counterparts.

Power Emission Enhancement of Light Emitting Diode by Using InN based Quantum Dot

This paper highlights the enhancement of emitted power from light emitting diodes using InN based quantum dot in the active layer of the device structure. We have developed mathematical models and analyzed numerically the temperature dependence of the degradation rate of the device lifetime, the effect of light transmission factor and the operating time on the power emitted from the light emitting diodes. The results obtained by using InN based quantum dot in the active layer of the device have been compared with those obtained by using InP based quantum dot in the active layer of the device. The comparison results reveal that the degradation rate of the device has been reduced and the power emission has been enhanced significantly by using InN based quantum dot in the active layer of the device. It can be then concluded that InN based quantun dot will bring a revolusionary changes in the performance improvement of LEDs in the near future.

Breakthroughs in Photonics 2014: Time-Scale-Dependent Nonlinear Dynamics in InAs/InP Quantum Dot Gain Media: From High-Speed Modulation to Coherent Light–Matter Interactions

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.

InP Based Quantum Dots for Long Wavelength Emissions and Their Post-Growth Bandgap Tuning

InP Based Quantum Dots for Long Wavelength Emissions and Their Post-Growth Bandgap Tuning

InP and Sn:InP based quantum dot sensitized solar cells

InP and Sn doped InP (Sn:InP) based quantum dot sensitized solar cells with a moderate efficiency were successfully fabricated.

Lasing characteristics of InP-based InAs quantum dots depending on InGaAsP waveguide conditions.

We report the influences of a dot-in-a-well structure with a thin GaAs layer and the thickness of a waveguide (WG) on the lasing characteristics of InAs quantum dots (QDs) based on InP. The QD laser diodes (QDLDs) consist of seven-stacked InAs QDs separated by a 10 nm-thick InGaAsP (1.15 μm, 1.15Q-InGaAsP) layer, which is further sandwiched by a 800 nm-thick 1.15Q-lnGaAsP WG (reference QDLD). For comparison, the InAs QDs were inserted into the InGaAsP (1.35 μm, 1.35Q-InGaAsP) quantum well embedded in the 1.15Q-InGaAsP matrix at the active layer. And a 2 monolayer (ML)-thick GaAs layer was additionally introduced right before the QD layer (GDWELL-LDs). Lasing emission from the reference QDLD with only the 1.15Q-InGaAsP structure was not observed at room temperature (RT). However, the lasing emission from the GDWELL-LDs was clearly observed at the wavelength of 1.46 μm at RT under continuous-wave (CW) mode. The threshold current density of the GDWELL-LD with the 800 nm-thick InGaAsP WG was measured to be 830 A/cm2, which was lower than that of the GDWELL-LD with the 200 nm-thick WG (900 A/cm2). Also, the slope efficiency of the GDWELL-LD was significantly improved with increasing thickness of the InGaAsP WG.

Thermal coefficient of InP-based quantum dot laser from cavity-mode measurements

The thermal coefficient of InP-based InAs quantum dot lasers covering its wavelength in the range of 1.55μm were reported. The measurements were based on analyzing the junction temperature in the active region. Under continuous wave mode, a more than 24°C junction temperature rise is obtained from the Fabry–Perot-cavity-mode shifts. The laser exhibits a coefficient of thermal resistance of 26.76°C/W when the injection current increases from 90 to 500mA. At the same time, a thermal resistivity of 8.62°Ccm/W with a thermal conductivity of 0.116W/cm°C was also obtained from the thermal resistance. The thermal resistance might be a crucial factor of quantum dot laser diodes and has greatly impact on their performance.

Intermixing of InP-based quantum dots and application to micro-ring resonator wavelength-selective filter for photonic integrated devices

In this study, we investigated quantum dot intermixing (QDI) for InAs/InGaAlAs highly stacked QDs on an InP(311)B substrate with low-temperature annealing at 650 °C in order to realize integrated photonic devices with QDs and passive waveguides. In particular, we adopted the method of introducing point defects by ICP-RIE to realize a blue shift of the PL peak wavelength by about 150 nm. Moreover, we successfully fabricated double micro-ring resonators by QDI. The output power contrasts of the devices were found to be 9.0 and 8.6 dB for TE and TM modes, respectively.

Low-density InP-based quantum dots emitting around the 1.5 μm telecom wavelength range

The authors report on low-density InAs quantum dots (QDs) grown on AlGaInAs surfaces lattice matched to InP using post-growth annealing by solid-source molecular beam epitaxy. Clearly spatially separated QDs with a dot density of about 5 × 108 cm−2 are obtained by using a special capping technique after the dot formation process. High-resolution micro-photoluminescence performed on optimized QD structures grown on distributed Bragg reflector exhibits single QD emissions around 1.5 μm with narrow excitonic linewidth below 50 μeV, which can be used as single photon source in the telecom wavelength range.

Telecom-wavelength (1.5 μm) single-photon emission from InP-based quantum dots

We demonstrate pronounced single-photon emission from InAs/AlGaInAs/InP quantum dots (QDs) at wavelengths above 1.5 μm that are compatible with standard long-distance fiber communication. The QDs are grown by molecular beam epitaxy on distributed Bragg reflectors. A low QD density of about 5 × 108 cm−2 was obtained using optimized growth conditions. Low-temperature micro-photoluminescence spectroscopy exhibits sharp excitonic emission lines from single QDs without the necessity of further processing steps. The combination of excitation power-dependent and polarization-resolved photoluminescence measurements reveal a characteristic exciton-biexciton behavior with biexciton binding energies that range from 3.5 to 4 meV and fine-structure splitting values down to 20 μeV.