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Hybrid perovskite light emitting diodes under intense electrical excitation
摘要： Hybrid perovskite semiconductors represent a promising platform for color-tunable light emitting diodes (LEDs) and lasers; however, the behavior of these materials under the intense electrical excitation required for electrically-pumped lasing remains unexplored. Here, we investigate methylammonium lead iodide-based perovskite LEDs under short pulsed drive at current densities up to 620 A cm?2. At low current density (J < 10 A cm?2), we ?nd that the external quantum ef?ciency (EQE) depends strongly on the time-averaged history of the pulse train and show that this curiosity is associated with slow ion movement that changes the internal ?eld distribution and trap density in the device. The impact of ions is less pronounced in the high current density regime (J > 10 A cm?2), where EQE roll-off is dominated by a combination of Joule heating and charge imbalance yet shows no evidence of Auger loss, suggesting that operation at kA cm?2 current densities relevant for a laser diode should be within reach.
关键词： ion movement,electrical excitation,lasers,Auger loss,light emitting diodes,Hybrid perovskite semiconductors,Joule heating,external quantum efficiency,charge imbalance
更新于2025-09-23 15:21:01
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Influence of precursor concentration and growth time on the surface morphology and crystallinity of α-Ga<sub>2</sub>O<sub>3</sub> thin films fabricated by mist chemical vapor deposition
摘要： Single-crystal thin films of gallium oxide (Ga2O3), an ultra-wide bandgap semiconductor, were fabricated on c-plane sapphire by mist chemical vapor deposition (mist CVD). The grown ?-Ga2O3 thin films had low surface roughness, and we characterized their initial crystal growth phase by using atomic force microscopy and X-ray diffraction. By varying the precursor concentration, we changed the surface roughness and crystallinity of the thin films. The lattice constants of the ?-Ga2O3 thin films almost matched those of the single crystal in the initial growth phase. We also found that these thin films grew hetero-epitaxially. Finally, mist CVD might have a very short incubation time in this system.
关键词： Gallium oxide,Surface morphology,Crystallinity,Precursor concentration,Mist chemical vapor deposition,Epitaxial growth,Wide bandgap semiconductors
更新于2025-09-23 15:21:01
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Single-layer planar penta-X2N4 (X= Ni, Pd and Pt) as direct-bandgap semiconductors from first principle calculations
摘要： Using first principle calculations we have investigated the structure stabilities, electronic and optical properties of single layer planar penta-X2N4 (X=Ni, Pd and Pt). According to the calculated phonon dispersion relation and elastic constants, as well as ab initio molecular dynamics simulation results, monolayers of planar penta-X2N4 are dynamically, mechanically, and thermally stable. In addition, these monolayers are direct-gap semiconductors with sizeable bandgaps ranging from 0.92 eV to 1.11 eV, which can be further tuned by external strains. Besides, the bonding characteristics and the optical properties in these monolayers are investigated based on HSE06 calculations, where strong in-plane optical absorption with wide spectral range has been revealed. Our results indicate that planar penta-X2N4 monolayers possess excellent electrical and optical properties, and may find potential applications in solar cells and nanoelectronics.
关键词： Electronic properties,First principle calculations,Optical properties,Direct-bandgap semiconductors,Planar penta-X2N4
更新于2025-09-23 15:21:01
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Hierarchical core-shell tungsten oxide/TiO2 nanowires as an effective photocatalyst
摘要： In this letter, tungsten oxide(WO3)/TiO2 core-shell nanowires were prepared by depositing a layer of TiO2 nanoparticles on the surface of WO3 nanowires via a pulse laser deposition method. These TiO2 nanoparticles are qusi-aligned wire-like structure on the surface of WO3 nanowires. The number of laser pulses during the deposition adjusts the TiO2 thickness. When used as photocatalyst, these core-shell nanowires have photocatalytic activity in the degradation of rhodamine B (RhB). The photo-induced electron-hole separation effect between WO3 and TiO2 contributes to the improvement of the photocatalystic activity. This makes these nanowire arrays having good potential in wastewater treatment.
关键词： Pulsed laser deposition,Nanocomposites,Semiconductors
更新于2025-09-23 15:21:01
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Carrier Generation in p-Type Wide-Gap Oxide: SnNb <sub/>2</sub> O <sub/>6</sub> Foordite
摘要： Wide-gap oxides with their valence band maximum (VBM) composed of s orbitals are essential for realizing practical p-type transparent oxide semiconductors. We prepared a new p-type wide-gap oxide, SnNb2O6 foordite, with its VBM composed of Sn 5s orbitals. To discuss carrier generation, we prepared both p-type and n-type SnNb2O6 by controlling the annealing conditions. The carrier mobility and density were 3.8 × 10?1 cm2 V?1 s?1 and 3.7 × 1018 cm?3, respectively, for the p-type sample and 9.9 cm2 V?1 s?1 and 7.5 × 1015 cm?3, respectively, for the n-type sample. The crystal structure of SnNb2O6 foordite consists of two types of alternating layers, Sn and Nb2O6 octahedra, where three nonequivalent oxygen sites exist. Six oxygens in the chemical formula of SnNb2O6 are distributed at the three sites in pairs, where the oxygens in three nonequivalent sites were named O1?O3. Hole and electron carriers were considered to be generated by Sn4+-on-Nb5+ substitutional defects (SnNb??) and oxygen vacancies of O1 and O2 that are not bonded to Sn (VO1/O2′), respectively. Therefore, we concluded that it is essential to control SnNb?? and VO1/O2′ to control the semiconducting properties such as the carrier type and carrier density.
关键词： wide-gap oxides,carrier generation,SnNb2O6 foordite,annealing conditions,p-type transparent oxide semiconductors
更新于2025-09-23 15:21:01
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Chemical and Biomolecule Sensing with Organic Field-Effect Transistors
摘要： The strong and controllable chemical sensitivity of organic semiconductors (OSCs) and the amplification capability of transistors in circuits make use of OSC-based field-effect transistors compelling for chemical sensors. Analytes detected and assayed range from few-atom gas-phase molecules that may have adverse health and security implications to biomacromolecules (proteins, nucleic acids) that may be markers for physiological processes and medical conditions. This review highlights recent progress in organic field-effect transistor (OFET) chemical sensors, emphasizing advances from the past 5 years and including aspects of OSC morphology and the role of adjacent dielectrics. Design elements of the OSCs and various formats for the devices are illustrated and evaluated. Challenges associated with the present state of the art and future opportunities are also discussed.
关键词： organic field-effect transistors,organic semiconductors,dielectrics,biomacromolecules,chemical sensors
更新于2025-09-23 15:21:01
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Evaluating intrinsic mobility from transient terahertz conductivity spectra of microcrystal samples of organic molecular semiconductors
摘要： In microcrystal samples of the prototypical organic molecular semiconductors rubrene and C10-DNTT (2,9-didecyl-dinaphtho[2,3-b:20,30-f]thieno[3,2-b]thiophene), we measured spectra of complex optical conductivity caused by photocarriers with optical-pump terahertz-probe spectroscopy. We analyzed the ~r xe T spectra using the Drude-Smith model and evaluated the DC mobility lDC, which includes extrinsic effects, and the intrinsic mobility lint. The resulting lDC and lint values are comparable to the mobility values obtained using transport measurements of polycrystalline and single-crystalline ?eld-effect transistors, respectively. This correspondence demonstrates that the intrinsic mobility values of organic molecular semiconductors can be evaluated from the measurements of microcrystal samples using transient terahertz spectroscopy.
关键词： mobility,C10-DNTT,organic molecular semiconductors,terahertz spectroscopy,rubrene
更新于2025-09-23 15:19:57
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Optical properties of metamorphic type-I InAs <sub/> 1? <i>x</i> </sub> Sb <sub/><i>x</i> </sub> /Al <sub/><i>y</i> ? </sub> In <sub/> 1? <i>y</i> ? </sub> As quantum wells grown on GaAs for the mid-infrared spectral range
摘要： We analyse the optical properties of InAs1?xSbx/Aly In1?y As quantum wells (QWs) grown by molecular beam epitaxy on relaxed Aly In1?y As metamorphic buffer layers (MBLs) using GaAs substrates. The use of Aly In1?y As MBLs allows for the growth of QWs having large type-I band offsets, and emission wavelengths >3 μm. Photoluminescence (PL) measurements for QWs having Sb compositions up to x = 10% demonstrate strong room temperature PL up to 3.4 μm, as well as enhancement of the PL intensity with increasing wavelength. To quantify the trends in the measured PL we calculate the QW spontaneous emission (SE), using a theoretical model based on an eight-band k·p Hamiltonian. The theoretical calculations, which are in good agreement with experiment, identify that the observed enhancement in PL intensity with increasing wavelength is associated with the impact of compressive strain on the QW valence band structure, which reduces the band edge density of states making more carriers available to undergo radiative recombination at fixed carrier density. Our results highlight the potential of type-I InAs1?xSbx/Aly In1?y As metamorphic QWs to address several limitations associated with existing heterostructures operating in the mid-infrared, establishing these novel heterostructures as a suitable platform for the development of light-emitting diodes and diode lasers.
关键词： light-emitting diode,k·p modelling,metamorphic heterostructure,mid-infrared,semiconductors,molecular beam epitaxy,photonics
更新于2025-09-23 15:19:57
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Deep Learning for Optoelectronic Properties of Organic Semiconductors
摘要： Atomistic modeling of the optoelectronic properties of organic semiconductors (OSCs) requires a large number of excited-state electronic-structure calculations, a computationally daunting task for many OSC applications. In this work, we advocate the use of deep learning to address this challenge and demonstrate that state-of-the-art deep neural networks (DNNs) are capable of accurately predicting various electronic properties of an important class of OSCs, i.e., oligothiophenes (OTs), including their HOMO and LUMO energies, excited-state energies and associated transition dipole moments. Among the tested DNNs, SchNet shows the best performance for OTs of different sizes, achieving average prediction errors in the range of 20-80meV. We show that SchNet also consistently outperforms shallow feed-forward neural networks, especially in difficult cases with large molecules or limited training data. We further show that SchNet could predict the transition dipole moment accurately, a task previously known to be difficult for feed-forward neural networks, and we ascribe the relatively large errors in transition dipole prediction seen for some OT configurations to the charge-transfer character of their excited states. Finally, we demonstrate the effectiveness of SchNet by modeling the UV-Vis absorption spectra of OTs in dichloromethane and a good agreement is observed between the calculated and experimental spectra.
关键词： optoelectronic properties,organic semiconductors,transition dipole moment,SchNet,oligothiophenes,deep learning,UV-Vis absorption spectra
更新于2025-09-23 15:19:57
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Resonance fluorescence of a single semiconductor quantum dot: the impact of a fluctuating electrostatic environment
摘要： Semiconductor quantum dots are very efficient sources of single and highly indistinguishable photons. These properties rely on the possibility to coherently control the system at the single spin level. At this ultimate level of control, the quantum dot becomes a very sensitive probe of its solid-state environment and any interaction turns into a dephasing process that alters its coherence properties. In this topical review, we give an overview of the issue of charge noise which remains one of the main dephasing mechanisms to overcome. This phenomenon which strongly depends on sample preparation, originates from a fluctuating electrostatic landscape around the quantum dots and renders a unified description quite awkward. We present the common characteristic features induced by charge noise that have been observed in the resonant fluorescence experiments of single quantum dots and discuss the different approaches that have been proposed in the literature to circumvent this problem.
关键词： quantum dots,quantum coherence,optical properties,resonance fluorescence,excitons,III–V semiconductors
更新于2025-09-23 15:19:57