Properties Of InP Quantum Dots Research Articles

Correction to “Synthesis, Surface Chemistry, and Fluorescent Properties of InP Quantum Dots”

Correction to “Synthesis, Surface Chemistry, and Fluorescent Properties of InP Quantum Dots”

Guilty as Charged: The Role of Undercoordinated Indium in Electron-Charged Indium Phosphide Quantum Dots.

Quantum dots (QDs) are known for their size-dependent optical properties, narrow emission bands, and high photoluminescence quantum yield (PLQY), which make them interesting candidates for optoelectronic applications. In particular, InP QDs are receiving a lot of attention since they are less toxic than other QD materials and are hence suitable for consumer applications. Most of these applications, such as LEDs, photovoltaics, and lasing, involve charging QDs with electrons and/or holes. However, charging of QDs is not easy nor innocent, and the effect of charging on the composition and properties of InP QDs is not yet well understood. This work provides theoretical insight into electron charging of the InP core and InP/ZnSe QDs. Density functional theory calculations are used to show that charging of InP-based QDs with electrons leads to the formation of trap states if the QD contains In atoms that are undercoordinated and thus have less than four bonds to neighboring atoms. InP core-only QDs have such atoms at the surface, which are responsible for the formation of trap states upon charging with electrons. We show that InP/ZnSe core-shell models with all In atoms fully coordinated can be charged with electrons without the formation of trap states. These results show that undercoordinated In atoms should be avoided at all times for QDs to be stably charged with electrons.

Synthesis, Surface Chemistry, and Fluorescent Properties of InP Quantum Dots

InP quantum dots (QDs) have great potential as emitters for solid-state lighting, lasing, and bioimaging without the inherent toxicity concern of Cd and Pb-based emitters. Indium phosphide’s small bandgap and high covalency make it uniquely capable of color-pure fluorescence that can be tuned throughout the visible and lower IR spectrum. Until recently, InP-based QDs consistently underperformed when compared with CdSe-based counterparts. Recent efforts to understand indium phosphide’s nonclassical growth mechanisms, control the nanocrystal shape, control in situ formation of surface oxides, and grow thick, uniform shells have produced InP-based QDs comparable to their CdSe competitors with >95% quantum yields (QYs) in red, green, and blue emission wavelengths. This review covers the most common synthetic techniques, the most recent theories on InP formation mechanisms, the current understanding of InP surface chemistries, and the breadth of fluorescent properties of InP-based QDs.

Zinc Oxo Clusters Improve the Optoelectronic Properties on Indium Phosphide Quantum Dots

This study explored the effect of zinc precursors on the optical properties of InP quantum dots (QDs) by controlling the reactivity of zinc carboxylates via a simple thermal treatment. The formatio...

Effect of the indium myristate precursor concentration on the structural, optical, chemical surface, and electronic properties of InP quantum dots passivated with ZnS

In this work, we present results on the synthesis and characterization of InP and InP@ZnS quantum dots (QDs), grown using a single-step chemical synthesis method without injection of hot precursors, varying the concentration of indium myristate in both cases. It was found a color variation of the QDs in solution due to the quantum confinement effects when the nanoparticle sizes are smaller than the exciton Bohr radius. The band-gap energy of the samples was determined from the absorption spectra. From the photoluminescence (PL) spectra, emission peaks located in the range from 2.1 to 3.0 eV were observed. Furthermore, an enhanced PL emission due to a passivation effect in the ZnS-covered InP QDs was obtained. From X-ray diffraction (XRD), it was shown the presence of crystalline phases of the InP, ZnS, and In2O3 nanoparticles, with sizes ranging from 8 to 10 nm as determined by high resolution transmission electron microscopy (HR-TEM). From X-ray photoelectron spectroscopy (XPS) analysis, it was confirmed the formation of InP, ZnS, and In2O3; moreover, by means of a valence band analysis, the electronic structure of the samples was further investigated. The effect of the indium myristate precursor concentration on the optical, structural, surface chemical, and electronic properties of InP and InP@ZnS QDs will be discussed.

Improving the ensemble optical properties of InP quantum dots by indium precursor modification

Indium phosphide quantum dots typically exhibit broad and poorly defined ensemble optical properties due to a highly pronounced nucleation period that consumes virtually all phosphorus precursors, leading to subsequent growth by Ostwald ripening and poor final size distributions. Previous attempts to reduce the reactivity of the phosphorus precursor, and thereby limit its consumption during the nucleation phase, have not led to appreciably better optical properties due to an unwanted increase in the duration of nucleation. Here we present an alternative approach to reducing initial precursor consumption using a simple modification of the indium precursor, in which the widely used carboxylate ligand is replaced by a phosphine. The change of ligand leaves residual precursor available for size-focusing growth after nucleation, leading to significantly improved spectral features. Band-edge emission peaks are typically 30% narrower than for the standard method.

Phosphine synthetic route features and postsynthetic treatment of InP quantum dots

In this paper we report on the development of synthesis of InP quantum dots with a gaseous phosphine PH3 as a source of phosphorus and myristic acid and TOP/TOPO as stabilizers. Samples synthesized using myristic acid as stabilizer at relatively low temperatures were found to contain admixture of In(OH)3. We studied the influence of HF concentration and duration of illumination on luminescence properties of InP quantum dots during photoetching process. Quantum yields of photoetched samples reached about 20%. Additionally, electrophoresis as a new technique of purification and size-depended separation of synthesized quantum dots was developed.

Modeling on the size dependent properties of InP quantum dots: a hybrid functional study

Theoretical calculations based on density functional theory were performed to provide better understanding of the size dependent electronic properties of InP quantum dots (QDs). Using a hybrid functional approach, we suggest a reliable analytical equation to describe the change of energy band gap as a function of size. Synthesizing colloidal InP QDs with 2–4 nm diameter and measuring their optical properties was also carried out. It was found that the theoretical band gaps showed a linear dependence on the inverse size of QDs and gave energy band gaps almost identical to the experimental values.

Effect of GaP and GaP/InGaP insertion layers on the structural and optical properties of InP quantum dots grown by metal-organic vapor phase epitaxy

A comparison of ultra-thin insertion layers (GaP and GaP/In0.4Ga0.6P) on InP self-assembled quantum dots (SAQDs) grown on GaAs (001) substrates using metal-organic vapor phase epitaxy (MOVPE) was studied. Atomic force microscopy (AFM) and photoluminescence (PL) were employed to characterize the optical and structural properties of the grown InP QDs. It is found that the QD dimension, size distribution and density strongly depend on the insertion layer thickness which led to tune the emission wavelength and narrowing of full width at half maximum (FWHM) at low temperature (20–250K) and at room-temperature PL measurements. This result is attributed to the improved QD size and quantum confinement effect arising from the insertion of the GaP and GaP/In0.4Ga0.6P layers.

Charge storage properties of InP quantum dots in GaAs metal-oxide-semiconductor based nonvolatile flash memory devices

Metal organic vapor phase epitaxially grown 5 nm InP quantum dots (QDs) were embedded as charge storage elements between high-k control and tunneling dielectric layers in GaAs metal-oxide-semiconductor based nonvolatile memory devices. The QDs trap more electrons resulting in a large memory window (6.3 V) along with low leakage due to Coulomb blockade effect. 16.5% charge loss was found even after 105 s indicating its good charge storing potential. The programming and erasing operations were discussed with proposed band diagram.

Optical and structural properties of InP quantum dots embedded in(AlxGa1−x)0.51In0.49P

Within this work we present optical and structural properties of InP quantum dots embedded in ${({\text{Al}}_{x}{\text{Ga}}_{1\ensuremath{-}x})}_{0.51}{\text{In}}_{0.49}\text{P}$ barriers. Atomic force microscopy measurements show a mainly bimodal height distribution with aspect ratios (ratio of width to height) of about 10:1 and quantum dot heights of around 2 nm for the smaller quantum dot class (type A) and around 4 nm for the larger quantum dot class (type B). From ensemble-photoluminescence measurements we estimated thermal activation energies of up to 270 meV for the type-A quantum dots, resulting in a 300 times higher luminescence intensity at 200 K in comparison to our InP quantum dots in ${\text{Ga}}_{0.51}{\text{In}}_{0.49}\text{P}$ at the same emission wavelength. Photon statistic measurements clearly display that InP quantum dots in ${({\text{Al}}_{0.20}{\text{Ga}}_{0.80})}_{0.51}{\text{In}}_{0.49}\text{P}$ emit single photons up to 80 K, making them promising candidates for high-temperature single-photon emitters.

Structural and optical properties of InP quantum dots grown on GaAs(001)

We investigated structural and optical properties of type-II InP/GaAs quantum dots using reflection high energy electron diffraction, transmission electron microscopy, atomic force microscopy, grazing incidence x-ray diffraction, and photoluminescence techniques. The InP dots present an efficient optical emission even when they are uncapped, which is attributed to the low surface recombination velocity in InP. We compare the difference in the optical properties between surface free dots, which are not covered by any material, with dots covered by a GaAs capping layer. We observed a bimodal dispersion of the dot size distribution, giving rise to two distinct emission bands. The results also revealed that the strain accumulated in the InP islands is slightly relieved for samples with large InP amounts. An unexpected result is the relatively large blue shift of the emission band from uncapped samples as compared to capped dots.

Structural and optical properties of InP quantum dots grown on GaAs (001)

AbstractWe present structural and optical properties of type‐II self‐assembled InP/GaAs quantum dots using different techniques. The results reveal that the uncapped InP dots present an efficient optical emission and are partially relaxed: strain relaxation increases with the amount of InP deposited. The photoluminescence spectra show two optical emission bands associated to the quantum dots, in agreement with the bi‐modal dot‐height distribution observed by atomic force microscopy. We observed distinct photoluminescence results for uncapped and capped samples, which are mainly attributed to surface state and strain relaxation effects. A remarkable result is the large blue shift of the optical emission band from uncapped sample as compared to capped one for increasing excitation intensities. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Improved area density and luminescence properties of InP quantum dots grown on In0.5Al0.5P by metal-organic chemical vapor deposition

We report on the growth of InP self-assembled quantum dots (QDs) on In0.5Al0.5P matrices by metal-organic chemical vapor deposition (MOCVD) on (001) GaAs substrates. The effects of the growth temperature and V/III-precursor flow ratio on the areal density and the cathodoluminescence (CL) properties of the grown QDs were systematically studied. We found that, when the growth temperature is ≤630°C, coherent QDs as well as large dislocated InP islands can be observed on the matrix surface. However, by using a two-step growth method, i.e., by growing the InAlP matrix layer at higher temperatures and growing InP QDs at lower temperatures, the formation of large dislocated islands can be effectively suppressed. Moreover, the areal density of the InP QDs is increased as the QD growth temperature is reduced. Furthermore, we found that the V/III ratio used in growing QDs and in growing the InAlP matrix layers has a quite different effect. In growing QDs, decreasing the V/III ratio results in an increase in the CL intensity and a decrease in CL line width; while in growing the InAlP matrix layers, increasing the V/III ratio results in an increase in the CL intensity of the InP QDs.

Effect of Si delta doping on the luminescence properties of InP/InAlP quantum dots

We show that the cathodoluminescence (CL) properties of InP quantum dots (QDs) grown on In0.5Al0.5P matrix layers, lattice-matched to (001) GaAs substrates, can be greatly improved by introducing silicon delta doping in the layer adjacent to the QDs. Under optimized conditions, the room-temperature CL intensity of QDs can be improved by ∼16 times. We speculate that the increased CL intensity is caused by the efficient capture of electrons from the reservoir of the delta-doped layer into the QDs, which, to some extent, counterbalances the thermal escape of electrons from the QDs. A temperature-dependent CL study of InP QDs grown without Si delta doping shows a quenching of the CL at high temperatures, which supports the unipolar escape of electrons from QDs, while delta-doped QDs show an anomalous behavior. The QD integrated CL intensity increases with temperature and then decreases after 200 K. This anomalous behavior is interpreted as caused by competition between two processes: (1) thermal activation of carriers out of the potential well introduced by delta doping and then capture by QDs, which enhances the CL intensity; and (2) quenching of the CL due to thermal activation of carriers out of the QDs.