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Phonon-assisted tunneling in direct-bandgap semiconductors
摘要： In tunnel ?eld-effect transistors, trap-assisted tunneling (TAT) is one of the probable causes for degraded subthreshold swing. The accurate quantum-mechanical (QM) assessment of TAT currents also requires a QM treatment of phonon-assisted tunneling (PAT) currents. Therefore, we present a multi-band PAT current formalism within the framework of the quantum transmitting boundary method. An envelope function approximation is used to construct the electron-phonon coupling terms corresponding to local Fr?hlich-based phonon-assisted inter-band tunneling in direct-bandgap III-V semiconductors. The PAT current density is studied in up to 100 nm long and 20 nm wide p-n diodes with the 2- and 15-band material description of our formalism. We observe an inef?cient electron-phonon coupling across the tunneling junction. We further demonstrate the dependence of PAT currents on the device length, for our non-self-consistent formalism which neglects changes in the electron distribution function caused by the electron-phonon coupling. Finally, we discuss the differences in doping dependence between direct band-to-band tunneling and PAT current.
关键词： phonon-assisted tunneling,quantum-mechanical modeling,tunnel ?eld-effect transistors,electron-phonon coupling,direct-bandgap semiconductors
更新于2025-09-23 15:22:29
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The Temperature Dependences of the Electron-Piezoelectric Potential Phonon Interacting System of Quasi Two Dimensional System in GaN and ZnS
摘要： We investigated theoretically the temperature dependence of the quantum optical transition of quasi 2-Dimensional Landau splitting system, in GaN and ZnS. We apply the Quantum Transport theory (QTR) to the system in the con?nement of electrons by square well con?nement potential. We use the projected Liouville equation method with Equilibrium Average Projection Scheme (EAPS). Through the analysis of this work, we found the increasing properties of Quantum Transition Line Shapes (QTLSs) and the Quantum Transition Line Widths (QTLWs) of CdS and GaN with the temperature we also found that QTLW, (cid:2)(cid:3)T (cid:4) of ZnS < (cid:2)(cid:3)T (cid:4) of GaN in (cid:5) = 394 (cid:6)m.
关键词： Quantum Transport Theory,Quantum Transition Line Widths (QTLW),Quantum Transition Line Shapes (QTLS),GaN and ZnS,Cyclotron Resonance,Equilibrium Average Projection Scheme (EAPS),Electron Phonon Coupling System
更新于2025-09-23 15:22:29
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Intense red emission and two-way energy transfer in Sm3+, Eu3+ co-doped NaLa(WO4)2 phosphors
摘要： NaLa(WO4)2 phosphors with various Eu3+ and Sm3+ concentrations were prepared via a molten salt method. The structure and luminescent properties of the prepared samples were analyzed by the X-ray diffraction (XRD) and fluorescence spectrophotometer. The results show that the crystal phase of all the prepared samples is single tetragonal crystal structure. The energy transfer type between Eu3+ ions is proved to be the exchange interaction and the electron-phonon coupling is weak. With the increase of the Sm3+ concentration, the energy transfer from Sm3+ to Eu3+ in NaLa(WO4)2:0.15Eu3+,xSm3+ is transformed from Eu3+ to Sm3+, and the mechanism for energy transfer is given.
关键词： Nanophosphor powders NaLa(WO4)2: xEu3+ ySm3+,Electron-phonon coupling,Photoluminescence,Energy transfer
更新于2025-09-23 15:21:21
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Ultrafast relaxation dynamics in bimetallic plasmonic catalysts
摘要： Combining a plasmonic metal, such as gold, with other popular catalysts, such as Ni or Pt, can extend its benefits to many energy-extensive reactions catalyzed by those metals. The efficiency of a plasmon-enhanced catalytic reaction is mainly determined by the light absorption cross section and the photo-excited charge carrier relaxation dynamics of the nanoparticles. We have investigated the charge carrier relaxation dynamics of gold/nickel (Au/Ni) and gold/platinum (Au/Pt) bimetallic nanoparticles. We found that the addition of Ni or Pt to gold can reduce light absorption in gold nanoparticles. However, electron–phonon coupling rates of Au/Ni and Au/Pt nanoparticles are significantly faster than that of pure Au nanoparticles. This is due to the fact that both Ni and Pt possess significantly larger electron–phonon coupling constants and higher densities of states near the Fermi level in comparison with Au. Additionally, the phonon–phonon coupling rate of bimetallic Au/Pt and Au/Ni nanoparticles was significantly different from that of pure gold nanoparticles, due to the acoustic impedance mismatch at the nanoparticle/substrate interface. Our findings provide important insights into the rational design of bimetallic plasmonic catalysts.
关键词： bimetallic nanoparticles,ultrafast relaxation dynamics,electron–phonon coupling,phonon–phonon coupling,plasmonic catalysts
更新于2025-09-23 15:21:01
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Remote Phononic Effects in Epitaxial Ruddlesden-Popper Halide Perovskites
摘要： Despite their weak nature, van der Waals (vdW) interactions have been shown to effectively control the optoelectronic and vibrational properties of layered materials. However, how vdW effects exist in Ruddlesden-Popper layered halide perovskites remains unclear. Here we reveal the role of interlayer vdW force in Ruddlesden-Popper perovskite in regulating phase transition kinetics and carrier dynamics, based on high-quality epitaxial single crystalline (C4H9NH3)2PbI4 flakes with controlled dimensions. Both substrate-perovskite epitaxial interaction and interlayer vdW interaction play significant roles in suppressing the structural phase transition. With reducing flake thickness from ~100 nm to ~20 nm, electron-phonon coupling strength decreases by ~30%, suggesting the ineffectiveness of phonon confinement of the natural quantum wells. Therefore, the conventional understanding that vdW perovskite is equivalent to a multiple quantum well has to be substantially amended due to significant nonlocal phononic effects in the layered crystal where intralayer interaction is not drastically different from the interlayer force.
关键词： phase transition,electron-phonon coupling,Ruddlesden-Popper perovskites,epitaxial growth,van der Waals interactions
更新于2025-09-23 15:21:01
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Impact of electrona??phonon coupling on the quantum yield of photovoltaic devices
摘要： In describing the charge carriers’ separation mechanism in the organic solar cell, providing a method, which considers the impact of all parameters of interest on the same footing within an inexpensive numerical effort, could play an essential role. We use here a simple tight-binding model to describe the dissociation of the charge carriers and investigate their dependence on the physical parameters of the system. We demonstrate that the quantum yield of the cell is subtly controlled by the collective action of the Coulomb interaction of the electron–hole pair, electron–phonon coupling, and the geminate recombination of the charge carriers. This approach should help us understand the performance of organic solar cells and optimize their efficiency.
关键词： electron–phonon coupling,quantum yield,organic solar cells,charge separation,photovoltaic devices
更新于2025-09-23 15:19:57
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Hydrothermal Synthesis and Luminescent Properties of Spindle-Like NaGd(MoO <sub/>4</sub> ) <sub/>2</sub> :Eu <sup>3+</sup> Phosphors
摘要： Spindle-like NaGd(MoO4)2: Eu3 + phosphors with various Eu3 + concentrations were prepared via a hydrothermal process and characterized using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). The XRD results suggested that the prepared samples had a scheelite structure. The FE-SEM images indicated that the prepared NaGd(MoO4)2: Eu3 + phosphors were spindle-like. The influences of the ratio of sodium citrate and the rare earth cations on the product were studied. It was found that sodium citrate, as the chelating agent, could significantly influence the structure and morphology of the samples. The emission spectra, excitation spectra, fluorescence decay curves, and quantum yields of the samples were measured. The luminescent properties of the materials were studied. The results indicated that the electron–phonon coupling between the Eu3 + and the NaGd(MoO4)2 host was weak, and with the increase of the Eu3 + concentration, the Huang–Rhys factor increased. Additionally, the quantum efficiency of the Eu3 + 5D0 level was calculated, and it was found that the quantum efficiency decreased with the increase of the Eu3 + concentration.
关键词： Electron-phonon coupling,Rare earth,Hydrothermal,Molybdate,Luminescence
更新于2025-09-19 17:15:36
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Soft Lattice and Defect Covalency Rationalize Tolerance of ?2a??CsPbI3 Perovskite Solar Cells to Native Defects
摘要： Although all-inorganic lead halide perovskite solar cells have shown tremendous improvement over the past few years, they are still inferior to the hybrid organic-inorganic perovskites in the solar power conversion efficiency. Recently, a conceptually new β-CsPbI3 perovskite has demonstrated an impressive 18.4% efficiency combined with good thermodynamic stability at ambient conditions. We use ab initio non-adiabatic molecular dynamics to show that native point defects in β-CsPbI3 are generally benign for nonradiative charge recombination, regardless of whether they introduce shallow or deep trap states. Moreover, formation of new covalently bound species in the presence of defects slows down the recombination. These results indicate that halide perovskites do not follow the simple models used to explain defect-mediated charge recombination in the conventional semiconductors. The strong tolerance of electron-hole recombination against defects arises due to the softness of the perovskite lattice, which permits separation of electrons and holes upon defect formation, and allows only low-frequency vibrations to couple to the electronic subsystem. Both factors decrease significantly the non-adiabatic coupling and slow down the dissipation of electronic energy to heat. We suggest that a halide-rich synthesis environment may further improve the efficiency, and propose that strong defect tolerance is general to metal halide perovskites because they exhibit much lower bulk moduli compared to the conventional semiconductors used in photovoltaic, photocatalytic, electrocatalytic, lasing, light-emitting, detecting and other opto-electronic devices.
关键词： Electron-phonon coupling,Nonradiative recombination,All-inorganic perovskites,Time-dependent density functional theory,Defects
更新于2025-09-19 17:13:59
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Phonon-Mediated and Weakly Size-Dependent Electron and Hole Cooling in CsPbBr <sub/>3</sub> Nanocrystals Revealed by Atomistic Simulations and Ultrafast Spectroscopy
摘要： We combine state-of-the-art ultrafast photoluminescence and absorption spectroscopy and nonadiabatic molecular dynamics simulations to investigate charge-carrier cooling in CsPbBr3 nanocrystals over a very broad size regime, from 0.8 nm to 12 nm. Contrary to the prevailing notion that polaron formation slows down charge-carrier cooling in lead-halide perovskites, no suppression of carrier cooling is observed in CsPbBr3 nanocrystals except for a slow cooling (over ~ 10 ps) of ‘warm’ electrons in the vicinity (within ~ 0.1 eV) of the conduction band edge. At higher excess energies, electrons and holes cool with similar rates, on the order of 1 eV ps-1 carrier-1 and increasing weakly with size. Our ab initio simulations suggest that cooling proceeds via fast phonon-mediated intra-band transitions driven by strong and size-dependent electron-phonon coupling. The presented experimental and computational methods yield the spectrum of involved phonons and may guide the development of devices utilizing hot charge carriers.
关键词： electron-phonon coupling,hot carriers,nonadiabatic molecular dynamics,Charge-carrier cooling,lead-halide perovskite nanocrystal,excited-states dynamics
更新于2025-09-19 17:13:59
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Contribution of electron-phonon coupling to the luminescence spectra of single colloidal quantum dots
摘要： Luminescence spectroscopy experiments were realized for single colloidal quantum dots CdSe/ZnS in a broad temperature range above room temperature in a nitrogen atmosphere. Broadening and shifts of spectra due to the temperature change as well as due to spectral diffusion processes were detected and analyzed. A linear correlation between the positions of maxima and the squared linewidths of the spectra was found. This dependence was explained by a model that takes into account the slow variation of the electron-phonon coupling strength.
关键词： temperature dependence,spectral diffusion,luminescence spectroscopy,electron-phonon coupling,colloidal quantum dots
更新于2025-09-12 10:27:22