Epitaxial Growth Research Articles

High growth rate metal organic chemical vapor deposition grown Ga2O3 (010) Schottky diodes

We report on the growth of Si-doped homoepitaxial β-Ga2O3 thin films on (010) Ga2O3 substrates via metal-organic chemical vapor deposition (MOCVD) utilizing triethylgallium (TEGa) and trimethylgallium (TMGa) precursors. The epitaxial growth achieved an impressive 9.5 μm thickness at 3 μm/h using TMGa, a significant advance in material growth for electronic device fabrication. This paper systematically studies the Schottky barrier diodes fabricated on the three MOCVD-grown films, each exhibiting variations in the epilayer thickness, doping levels, and growth rates. The diode from the 2 μm thick Ga2O3 epilayer with TEGa precursor demonstrates promising forward current densities, the lowest specific on-resistance, and the lowest ideality factor, endorsing TEGa’s potential for MOCVD growth. Conversely, the diode from the 9.5 μm thick Ga2O3 layer with TMGa precursor exhibits excellent characteristics in terms of lowest leakage current, highest on-off ratio, and highest reverse breakdown voltage of −510 V without any electric field management, emphasizing TMGa’s suitability for achieving high growth rates in Ga2O3 epilayers for vertical power electronic devices.

SPECIFICS OF DESIGNING AN INFRARED PYROMETER-REFLECTOMETER FOR SEMICONDUCTOR HETEROSTRUCTURE FABRICATION

There are general technical requirements for all types of reactors for chemical vapour deposition technology using AIII- BV metalorganic compounds. Among them, it is worth highlighting the large temperature gradients that cause the origin of convection loops, which in turn, taking into account the high speed of the gas flow, lead to turbulence in the reactor instead of the expected laminar flow. It is also important to take into account the change in parameters of the wafer surface during the growth process and the need for signal separation between the useful signal from the wafer surface and the background signal from the wafer carrier, which rotates at fixed speed for uniform deposition of compounds. To obtain high-quality heterostructures with reproducible parameters, it is important to have a system of precise temperature control on the wafer surface directly in the deposition area, since the deposition process for many complex semiconductor devices (for example, laser diodes, LEDs, photodiodes, transistors on heterojunctions) is very sensitive to temperature changes. The method of optical pyrometry is a non-contact method that allows to precisely determine the temperature of the wafer surface and meets the technical requirements of CVD epitaxy growth reactors. This article is devoted to the analysis of the features of the development of optoelectronic systems for precise temperature measurement during epitaxial growth in order to determine the criteria for the selection or development of components of the optoelectronic system of the pyrometer-reflectometer. The main physical processes, electro-optical characteristics of Si photodiode, AlGaAs/GaAs LED and parameters of bandpass interference filters were investigated. Based on the analysis of the obtained research and measurement results, scientific recommendations have been developed. The recommendations aimed at the selection and optimization of the parameters of the components of the pyrometer-reflectometer (photodetectors, light emitting diodes, optical filters) in order to improve the accuracy and temperature stability of measurements in the pyrometer’s operation conditions, which take into account the compensation of emissivity change from the surface of the wafer.

Fast growth of large-sized organic single crystals via spin coating

Spin-coating stands out as one of the fastest and simplest processes for material solidification. While it is commonly employed for producing polycrystalline thin films, recent endeavors have explored its potential for epitaxial growth, albeit primarily limited to inorganic materials. In this study, we demonstrate the spin-coating method enabling the rapid growth of large-sized organic single crystals (OSCs). Within 2 h, we successfully obtained OSCs with controlled lateral sizes of up to 2 mm, which conventionally takes several weeks using slow solvent evaporation. Raman mapping and UV–Vis absorption measurements confirmed the growths of the OSCs. We propose the growth mechanism by using the supersaturated dynamic fluid model. Furthermore, we demonstrate the device integration of these OSCs for charge-transfer complex channel, revealing ambipolar behavior during gate sweep. This innovative OSCs production method has the potential to advance the various field of science and electronics, traditionally hindered by the scarcity of adequately sized OSCs.

MBE growth of Ge1−x Sn x devices with intrinsic disorder

We discuss the electrical properties of molecular beam epitaxy (MBE) grown, modulation doped, Ge1−x Sn x quantum well devices. A consequence of the epitaxial growth process is that electronic disorder is introduced even in modulation doped quantum well structures and electrical transport properties that are characteristic of a high level of disorder are apparent. MBE growth of this material also results in the surface segregation of elemental β-Sn in the way that has been observed utilizing other epitaxial growth methods. A thermally activated, p-type mobility is a clear feature of the electrical properties with generally temperature independent hole densities ∼1012 cm−2 from the measured Hall effect and coming from the modulation doping. We present a discussion of Hall effect measurements in this disordered regime. The percolation carrier density in MBE modulation doped GeSn is in the region of ∼1 × 1012 cm−2 although Hall measurements in this regime are difficult to quantify when the resistivity >(h/e 2). In this notation h is Planck’s constant and e is the unit of charge. Conductivities (σ) as low as ∼0.028 × (e 2/h) × square can be measured in the four-contact ac configuration and the temperature dependence indicates a mobility edge in these p-type devices below ∼2 × 1012 cm−2. At lower temperatures (<∼1 K) the presence of a Coulomb gap can be determined using dc transport, constant voltage measurements where small ac current excitation is not available experimentally. This two-contact configuration can determine σ down to ∼10−6 × (e 2/h), deep into the localization regime, revealing a hopping conductivity dominated system. We discuss the relevance of these electrical properties for MBE grown GeSn devices.

Edge‐Rich Pt‐O‐Ce Sites in CeO2 Supported Patchy Atomic‐Layer Pt Enable a Non‐CO Pathway for Efficient Methanol Oxidation

Rational design of efficient methanol oxidation reaction (MOR) catalyst that undergo non‐CO pathway is essential to resolve the long‐standing poisoning issue. However, it remains a huge challenge due to the rather difficulty in maximizing the non‐CO pathway by the selective coupling between the key *CHO and *OH intermediates. Here, we report a high‐performance electrocatalyst of patchy atomic‐layer Pt epitaxial growth on CeO2 nanocube (Pt ALs/CeO2) with maximum electron‐metal support interactions for enhancing the coupling selectively. The small‐size monolayer material achieves an optimal geometrical distance between edge Pt‐O‐Ce sites and *OH absorbed on CeO2, which well restrains the dehydrogenation of *CHO, resulting in the non‐CO pathway. Meanwhile, the *CHO/*CO intermediate generated at inner Pt‐O‐Ce sites can migrate to edge, inducing the subsequent coupling reaction, thus avoiding poisoning while promoting reaction efficiency. Consequently, Pt ALs/CeO2 exhibits exceptionally catalytic stability with negligible degradation even under 1000 s pure CO poisoning operation and high mass activity (14.87 A/mgPt), enabling it one of the best‐performing alkali‐stable MOR catalysts.

Lattice Matching and Microstructure of the Aromatic Amide Fatty Acid Salts Nucleating Agent on the Crystallization Behavior of Recycled Polyethylene Terephthalate.

To solve the decrease in the crystallization, mechanical and thermal properties of recycled polyethylene terephthalate (rPET) during mechanical recycling, the aromatic amide fatty acid salt nucleating agents Na-4-ClBeAmBe, Na-4-ClBeAmGl and Na-4-ClAcAmBe were synthesized and the rPET/nucleating agent blend was prepared by melting blending. The molecular structure, the thermal stability, the microstructure and the crystal structure of the nucleating agent were characterized in detail. The differential scanning calorimetry (DSC) result indicated that the addition of the nucleating agent improved the crystallization temperature and accelerated the crystallization rate of the rPET. The nucleation efficiencies (NE) of the Na-4-ClBeAmBe, Na-4-ClBeAmGl and Na-4-ClAcAmBe were increased by 87.2%, 87.3% and 41.7% compared with rPET which indicated that Na-4-ClBeAmBe and Na-4-ClBeAmGl, with their long-strip microstructures, were more conducive to promoting the nucleation of rPET. The equilibrium melting points (Tm0) of rPET/Na-4-ClBeAmBe, rPET/Na-4-ClBeAmGl and rPET/Na-4-ClAcAmBe were increased by 11.7 °C, 18.6 °C and 1.9 °C compared with rPET, which illustrated that the lower mismatch rate between rPET and Na-4-ClBeAmGl (0.8% in b-axis) caused Na-4-ClBeAmGl to be the most capable in inducing the epitaxial crystallization and orient growth along the b-axis direction of the rPET. The small angle X-ray diffraction (SAXS) result proved this conclusion. Meanwhile, the addition of Na-4-ClBeAmGl caused the clearest increase in the rPET of its flexural strength and heat-distortion temperature (HDT) at 20.4% and 46.7%.

Flexible and highly-loaded mixed-matrix membrane with bi-continuous metal–organic frameworks transfer pathway for gas separation

Highly-loaded metal–organic frameworks (MOFs) based mixed matrix membranes (MMMs) are essential for high-efficiency gas separation. However, the continuous distribution of MOFs across the membrane with intensified interface remains challenging. Herein, a flexible and defects-free MMM with a bi-continuous MOFs pathway is constructed by dopamine (DA)-assisted MOFs growth along nanofibers. Nanofibers are used to upload and distribute ZIF-8, which continues to grow via an epitaxial growth strategy to obtain ZIF-8 fibers, achieving ZIF-8 continuous both in long and short range. DA promotes heterogeneous nucleation and growth of ZIF-8 on fiber surface by chelating with Zn2+ through –OH and –NH2 groups. DA also ensures excellent interfacial compatibility by hydrogen bonding interaction between amino groups of DA and ether-oxygen groups of PEO. Finally, the highly-loaded MMM is constructed by in-situ photopolymerization of Poly (ethylene glycol) diacrylate) to embrace ZIF-8 fibers tightly. The resultant MMM presents ZIF-8 loading as high as 72.41 vol% with Young’s modulus of 33.42 MPa, and unchanged morphology and separation performances after bending for 180° over 50 times, revealing outstanding mechanical properties. The CO2 permeability and CO2/N2 selectivity are 280.3 % and 73.0 % higher than the PEO membrane, surpassing the 2019 McKeown upper bound.

Epitaxial Growth of Monolayer SnP3 with High Mobility and Chiral Boundary Junctions.

Two-dimensional materials with layered structures, appropriate band gaps, and high carrier mobility have attracted tremendous interest for their potential applications. Here we report the growth of monolayer SnP3 on Au(111) surfaces by molecular beam epitaxy. The kinetic processes for the growth and the crystalline properties are studied by scanning tunneling microscopy. The weak interaction between SnP3 and its Au(111) substrate is signified by the random crystal orientation distributions of SnP3 nanosheets. The electronic structures exhibit a band gap of ∼0.25 eV and high charge carrier mobility comparable to that of black phosphorus engineered by compressive strain. Additionally, domain boundary junctions with opposite chirality are observed, resulting from the strained film in the epitaxial growth process. Our work provides a method to fabricate high-quality monolayer SnP3 and suggests that the monolayer SnP3 is a promising candidate for applications in nanoelectronics and optoelectronics.

Into the Void: Single Nanopore in Colloidally Synthesized Bi2Te3 Nanoplates with Ultralow Lattice Thermal Conductivity.

Bi2Te3 is a well-known thermoelectric material that was first investigated in the 1960s, optimized over decades, and is now one of the highest performing room-temperature thermoelectric materials to-date. Herein, we report on the colloidal synthesis, growth mechanism, and thermoelectric properties of Bi2Te3 nanoplates with a single nanopore in the center. Analysis of the reaction products during the colloidal synthesis reveals that the reaction progresses via a two-step nucleation and epitaxial growth: first of elemental Te nanorods and then the binary Bi2Te3 nanoplate growth. The rates of epitaxial growth can be controlled during the reaction, thus allowing the formation of a single nanopore in the center of the Bi2Te3 nanoplates. The size of the nanopore can be controlled by changing the pH of the reaction solution, where larger pores with diameter of ∼50 nm are formed at higher pH and smaller pores with diameter of ∼16 nm are formed at lower pH. We propose that the formation of the single nanopore is mediated by the Kirkendall effect and thus the reaction conditions allow for the selective control over pore size. Nanoplates have well-defined hexagonal facets as seen in the scanning and transmission electron microscopy images. The single nanopores have a thin amorphous layer at the edge, revealed by transmission electron microscopy. Thermoelectric properties of the pristine and single-nanopore Bi2Te3 nanoplates were measured in the parallel and perpendicular directions. These properties reveal strong anisotropy with a significant reduction to thermal conductivity and increased electrical resistivity in the perpendicular direction due to the higher number of nanoplate and nanopore interfaces. Furthermore, Bi2Te3 nanoplates with a single nanopore exhibit ultralow lattice thermal conductivity values, reaching ∼0.21 Wm-1K-1 in the perpendicular direction. The lattice thermal conductivity was found to be systematically lowered with pore size, allowing for the realization of a thermoelectric figure of merit, zT of 0.75 at 425 K for the largest pore size.

Synthesis of epitaxial LuN films

Epitaxy of rare-earth nitride films are crucial for studying their physical properties and offer significant potential for applications in spintronics and optoelectronics. However, synthesizing single-crystalline LuN presents significant challenges, leading to a limited understanding of its properties. In this study, we successfully achieved the epitaxial growth of (001)-oriented LuN films on YAlO3 (110) substrates by reactive magnetron sputtering epitaxy. Electrical transport measurement at low temperatures reveals that the LuN film exhibits semiconducting behavior between 300 K and 2 K, with an activation energy of approximately 0.01 eV. Notably, negative magnetoresistance was observed below 12 K, which can result from the defects and magnetic impurities in LuN films. Our results uncover the electronic and magnetic properties of epitaxial LuN films.

Nest-Scheme RuIrLa Nanocrystals by NP-to-NP Oriented Assembly: Coherent Strain Fields-Driven Band Structure Splitting for Efficient Acidic Water Oxidation.

Atomic substructure engineering provides new opportunities for the designing newly and efficient catalysts with diverse atom ensembles, trimmed electron bands, and way-out coordination environments, creating unique contributing to concertedly catalyze water oxidation, which is of great significance for proton exchange membrane water electrolysis (PEMWE). Herein, nest-scheme RuIrLa nanocrystals with dense coherent interfaces as built-in substructures are firstly fabricated by using commercial ZnO particles as acid-removable templates, through a La-stabilized coherent epitaxial growth of nanoparticles (NPs). The obtained nests exhibit a low overpotential of 198mV at 10mA cm-2, and the RuIrLa||Pt/C module equipped in PEMWE operates stably at a cell voltage potential of 1.69V at 100mA cm-2 in 0.5M H2SO4 for 55h, which is far beyond the current IrO2||Pt/C. Within the nests, the position at the interface shows high tensile/compressive strain, significantly reducing the OER activation energy. More importantly, the La termination-stabilized coherent interfaces within the nests creates a unique self-healing process for the outstanding long-term stability. This work provides a promising substructure engineering to develop efficient catalysts with abundant substructures, such as coherent interfaces, dislocations, or grain boundaries, thereby realizing concerted improvement of activity and durability toward water oxidation.

Three-dimensionally oriented organization of hexagonal MIL-96 microplates toward superior film microstructure

Preferential orientation control of MOF films is advantageous for maximizing pore uniformity and minimizing grain boundary defects. Nonetheless, the preparation of MOF films with both in-plane and out-of-plane orientations remains a grand challenge. In this study, we reported the preparation of three-dimensionally oriented MIL-96 layers through combining morphology control of MIL-96 seeds with addition of PVP surfactants and arachidonic acids. Three-dimensionally oriented MIL-96 film was readily obtained through in-plane epitaxial growth. It is anticipated that the above protocol can be effective for obtaining diverse MOF films with three-dimensionally oriented organization.

Sustainable fabrication of highly (110)-oriented ZIF-8 membrane via supercritical fluid processing

Preferred orientation control represents a crucial step for performance enhancement of MOF membranes. Nevertheless, their sustainable preparation remains a significant challenge. In this work, we fabricated highly (110)-oriented ZIF-8 membranes through supercritical fluid (SCF)-assisted epitaxial growth of oriented seed layer. Benefiting from unique physicochemical properties and intrinsic chemical inertness of supercritical CO2, preferential orientation originated from the seed layer could be well maintained during epitaxial SCF processing; moreover, both unreacted ligands and discharged CO2 could be efficiently recovered, resulting in zero pollutant emission. Our ZIF-8 membrane exhibited ideal C3H6/C3H8 selectivity of 91.8. To the best of our knowledge, this represented the first report of the preparation of highly oriented ZIF-8 membrane with such high C3H6/C3H8 selectivity; more importantly, our study demonstrated that SCF processing represented an effective protocol for orientation modulation of MOF membranes towards superior separations.

Improving luminescence response in ZnGeN2/GaN superlattices: defect reduction through composition control

Color-mixed (cm) light-emitting diodes (LEDs) are theoretically the most efficient white light emitters, projected to improve white light luminous efficacy by 34% compared to incumbent phosphor converted LEDs. Since white light technology is pervasive and essential, small improvements in LED technology can result in energy savings. However, cm-LEDs are not yet realized due to poor efficacy in green and amber emitting materials, a spectral region colloquially referred to as the Green Gap. ZnGeN2 is nearly isostructural and closely lattice-matched to GaN and can be heteroepitaxially integrated with existing GaN devices; ZnGeN2/GaN hybrid structures are theorized to emit green (~530 nn) light with a spontaneous emission rate 4.6–4.9 times higher than traditional InGaN LEDs when incorporated into III-N LED structures. In this report we demonstrate the molecular beam epitaxy (MBE) growth of GaN and ZnGeN2 superlattices, an important step towards realizing multiple quantum well structures required for efficient LEDs. Elemental analysis, including atom probe tomography, shows that Ga and Ge are observed in both ZnGeN2 and GaN layers, degrading the structural uniformity. The lack of elemental abruptness also leads to increased defect luminescence and reabsorption of band edge luminescence. The source of unintentional Ga distributed throughout the ZnGeN2 layers was identified as excess flux escaping from around the closed MBE shutter. The source of unintentional Ge, which tended to incorporate as a single delta-doped layer in GaN, was identified as Ge riding along the cyclical metal-rich Ga adlayer used for high quality GaN, incorporating during subsequent nitrogen-rich growth step. Modifying the growth strategy results in improved structural quality, elemental abruptness, and luminescence response. This realization of structurally and elementally abrupt interfaces demonstrates the potential of heteroepitaxially integrated binary and ternary nitrides for energy-relevant devices.

Growth of 1D Carbon Nanotube@Perovskite Core–Shell van der Waals Heterostructures through Chemical Vapor Deposition

AbstractPerovskite is an emerging material with immense potential in the field of optoelectronics. 1D perovskite nanowires are crucial building blocks for the development of optoelectronic devices. However, producing perovskite nanowires with high quality and controlled alignment is challenging. In this study, the direct epitaxial growth of perovskite on oriented carbon nanotube (CNT) templates is presented through a chemical vapor deposition method. The deposition process of lead iodide and methylammonium iodide is systematically investigated, and a layer plus island growth mechanism is proposed to interpret the experimental observations. The aligned long CNTs serve as 1D templates and allow the growth of CNT@perovskite core‐shell heterostructure with a high aspect ratio to withstand large deformation. The obtained 1D perovskite materials can be easily manipulated and transferred, enabling the facile preparation of microscale flexible devices. For proof of concept, a photodetector based on an individual CNT@methylammonium lead iodide heterostructure is fabricated. This work provides a new approach to prepare 1D hetero‐nanostructure and may inspire the design of novel flexible nanophotodetectors.

Monomolecular Membrane-Assisted Growth of Antimony Halide Perovskite/MoS2 Van der Waals Epitaxial Heterojunctions with Long-Lived Interlayer Exciton.

Epitaxial growth stands as a key method for integrating semiconductors into heterostructures, offering a potent avenue to explore the electronic and optoelectronic characteristics of cutting-edge materials, such as transition metal dichalcogenide (TMD) and perovskites. Nevertheless, the layer-by-layer growth atop TMD materials confronts a substantial energy barrier, impeding the adsorption and nucleation of perovskite atoms on the 2D surface. Here, we epitaxially grown an inorganic lead-free perovskite on TMD and formed van der Waals (vdW) heterojunctions. Our work employs a monomolecular membrane-assisted growth strategy that reduces the contact angle and simultaneously diminishing the energy barrier for Cs3Sb2Br9 surface nucleation. By controlling the nucleation temperature, we achieved a reduction in the thickness of the Cs3Sb2Br9 epitaxial layer from 30 to approximately 4 nm. In the realm of inorganic lead-free perovskite and TMD heterojunctions, we observed long-lived interlayer exciton of 9.9 ns, approximately 36 times longer than the intralayer exciton lifetime, which benefited from the excellent interlayer coupling brought by direct epitaxial growth. Our research introduces a monomolecular membrane-assisted growth strategy that expands the diversity of materials attainable through vdW epitaxial growth, potentially contributing to future applications in optoelectronics involving heterojunctions.

Development of ATP-modified CoFe2O4@ZIF-8@ZIF-67 core–shell nanozyme for sensitive colorimetric detection of dopamine

Core-shell nanostructures (NSs) are a type of nanozyme broadly used in various fields due to their significant physicochemical advantages. In the present study, the CoFe2O4@ZIF-8@ZIF-67 core–shell were fabricated by a consecutive two-step synthesis method, including hydrothermal for CoFe2O4 metal spinel and epitaxial solvothermal growth of ZIFs bilayers on the metal spinel NSs. The core–shell surface was modified using ATP inspired by the active site of the natural peroxidase enzyme. The nanocomposites were characterized by XRD, FT-IR, SEM, EDX, and Dot-mapping techniques. The peroxidase-like activity of the ATP/CoFe2O4@ZIF-8@ZIF-67 was assessed by a colorimetric method. Modified nanocomposite displayed desirable peroxidase mimetic activity and could enzymatically generate hydroxyl radicals from H2O2 and oxidize TMB. The high catalytic activity of ATP-modified nanocomposite and its ability to oxidize TMB provides a rapid and sensitive platform for the colorimetric detection of dopamine. Dopamine consumes hydroxyl radicals, prevents TMB oxidation, and causes a color change in the detection solution, which the naked eye can recognize. The presented colorimetric test provided an excellent LOD for dopamine (0.4 µM) with a good linear range (0.2–18 µM) and selectivity, which was prosperously applied to dopamine assay in serum blood samples.

Van der Waals epitaxial growth of few layers WSe2 on GaP(111)B

2D material epitaxy offers the promise of new 2D/2D and 2D/3D heterostructures with their own specific electronic and optical properties. In this work, we demonstrate the epitaxial growth of few layers WSe2 on GaP(111)B by molecular beam epitaxy. Using a combination of experimental techniques, we emphasize the role of the growth temperature and of a subsequent annealing of the grown layers under a selenium flux on the polytype formed and on its structural and morphological properties. We show that a low growth temperature promotes the formation of the 1T′ and 3R phases depending on the layer thickness whereas a higher growth temperature favours the stable 2H phase. The resulting layers exhibit clear epitaxial relationships with the GaP(111)B substrate with an optimum grain disorientation and mean size of 1.1° and around 30 nm respectively for the 2H phase. Bilayer 2H WSe2/GaP(111)B heterostructures exhibit a staggered type II band alignment and p-doped character of the epi-layer on both p and n-type GaP substrates. This first realisation of stable p-type WSe2 epi-layer on a large-area GaP(111)B substrate paves the way to new 2D/3D heterostructures with great interests in nanoelectronic and optoelectronic applications, especially in the development of new 2D-material p-n junctions.

Spatially Resolved Multicolor Luminescence Tuning on the Single 1D Heterogeneous Microrod.

The spatially resolvable multicolored microrods have potential applications in many fields. However, achieving spatially resolved multicolor luminescence tuning on the microrod with a fixed composition remains a daunting challenge. Herein, a strategy is proposed that allows for the tuning of spatially resolved, multicolored upconversion (UC) luminescence (UCL) along a 1D heterogeneous microrod by modifying the pulse width of an external laser. NaYbF4:1 % Ho is identified as an UCL color-adjustable material, exhibiting pulse width-dependent multicolored UCL, resulting in a significant regulation of the red/green (R/G) ratio from 0.1 to 10.3 as the pulse width is varied from 0.1 to 10 ms. Such variability can be ascribed to differences in the number of photons incident upon the microrod throughout the period necessary for the UC process to occur. Additionally, NaYbF4:1 %Tm and NaYF4:20 %Yb,1 %Ho are employed as materials that emit blue and green light, respectively, with their UCL colors largely unaffected by changes in the pulse width. Subsequently, a tip-modified epitaxial growth method is utilized to integrate both UCL color-adjustable and non-adjustable segments within the same microrod. Comparing with single-color or fixed multicolor microrods, our developed multisegmented emissive color adjustable 1D heterogeneous microrods have unique optical characteristics and can carry more optical information.

Near-Infrared-to-Visible Photon Upconversion with Efficiency Exceeding 21% Sensitized by InAs Quantum Dots.

Upconversion (UC) of incoherent near-infrared (NIR) photons to visible photons through sensitized triplet-triplet annihilation (TTA) shows great potential in solar energy harvesting, photocatalysis, and bioimaging. However, the efficiencies of NIR-to-visible TTA-UC systems lag considerably behind those of their visible-to-visible counterparts. Here, we report a novel NIR-to-yellow TTA-UC system with a record quantum yield (QY) of 21.1% (out of a 100% maximum) and a threshold intensity of 20.2 W/cm2 by using InAs-based colloidal quantum dots (QDs) as triplet photosensitizers. The key to success is the epitaxial growth of an ultrathin ZnSe shell on InAs QDs that passivates the surface defects without impeding triplet energy transfer (TET) from QDs to surface-bound tetracene. Transient absorption spectroscopy verifies efficient TET efficiency of more than 80%, along with sufficiently long triplet lifetime of tetracene molecules, leading to high-performance UC. Moreover, high UC QYs (>18%) remain when larger InAs-based QDs─of which the absorption peak is red-shifted by more than 50 nm─are used as sensitizers, indicating the great potential of InAs QDs to utilize NIR photons with lower energy.