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Multiphonon trap ionization transport in nonstoichiometric SiN<i><sub>x</sub></i>
摘要： It is generally accepted that the charge transport in dielectrics is governed by coulombic trap ionization due to a barrier lowering in high electric fields (Frenkel effect). In this paper, the charge transport mechanism in Si3N4 and nonstoichiometric silicon rich SiNx is experimentally studied and quantitatively analyzed with five theoretical models: Frenkel model of Coulomb traps ionization, Hill-Adachi model of overlapping Coulomb traps, Shklovskii-Efros percolation model, Makram-Ebeid and Lannoo model of multiphonon isolated traps ionization and Nasyrov-Gritsenko model of phonon-assisted electron tunneling between nearby traps. It is shown that the charge transport in Si3N4 and SiNx is qualitatively described by Frenkel effect, but Frenkel effect predicts an enormously low attempt to escape factor value. The charge transport at traps energies Wt=1.6 eV and Wopt=3.2 eV in Si3N4 and SiNx can be described by an increase in traps concentration in the framework of Makram-Ebeid and Lannoo model and Nasyrov-Gritsenko model. The Makram-Ebeid and Lannoo model quantitatively describes the charge transport in Si3N4 and SiNx with low silicon enrichment. The charge transport in nonstoichiometric SiNx with high silicon enrichment is well explained by Nasyrov-Gritsenko model.
关键词： charge transport,traps ionization,percolation,traps
更新于2025-09-09 09:28:46
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Semiconducting polymer blends that exhibit stable charge transport at high temperatures
摘要： Although high-temperature operation (i.e., beyond 150°C) is of great interest for many electronics applications, achieving stable carrier mobilities for organic semiconductors at elevated temperatures is fundamentally challenging. We report a general strategy to make thermally stable high-temperature semiconducting polymer blends, composed of interpenetrating semicrystalline conjugated polymers and high glass-transition temperature insulating matrices. When properly engineered, such polymer blends display a temperature-insensitive charge transport behavior with hole mobility exceeding 2.0 cm2/V·s across a wide temperature range from room temperature up to 220°C in thin-film transistors.
关键词： semiconducting polymer blends,charge transport,thermal stability,high-temperature operation,organic semiconductors
更新于2025-09-04 15:30:14
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Two-dimensional semimetal in HgTe quantum well under hydrostatic pressure
摘要： We report results of systematic measurements of charge transport properties of the 20.5-nm-wide HgTe-based quantum well in perpendicular magnetic ?eld, performed under hydrostatic pressures up to 15.1 kbar. At ambient pressure, transport is well described by the two-band semiclassical model. In contrast, at elevated pressure, we observed nonmonotonic pressure dependence of resistivity at the “charge neutrality point.” For pressures lower than ≈9 kbar, resistivity grows with pressure, in accord with expectations from the band structure calculations and the model incorporating effects of disorder on transport in two-dimensional (2D) semimetals with indirect band overlap. For higher pressures, the resistivity saturates and starts decreasing upon further increase of pressure. Above ≈14 kbar the resistance value and the magnetoresistance character sharply change, which may indicate signi?cant change of electronic structure due to new electronic phase formation or some structural transitions. The data also reveal strong in?uence of disorder on transport in 2D electron-hole system with a small band overlap.
关键词： HgTe quantum well,charge transport,hydrostatic pressure,magnetoresistance,two-dimensional semimetal
更新于2025-09-04 15:30:14
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Synthesis and investigation of charge transport properties in adducts of hole transporting carbazole derivatives and push-pull azobenzenes
摘要： In order to investigate the viability of a material design for bulk heterojunction (BHJ) organic solar cells, where hole transporting group is bound to the donor moiety, we report the synthesis and charge transport characteristics of 3-(diphenylamino)carbazolyl- functionalized derivatives of 2-(4-((4-(dimethylamino)phenyl)diazenyl)benzylidene)-1H-indene-1,3-dione (DMAAzi) chromophore. Three different bounding configurations were examined in these adducts. Additionally, a trityl- functionalized derivative of DMAAzi was prepared and used for comparison purposes. All of the synthesized materials form thin amorphous films from volatile organic solvents and exhibit glass transition temperatures in the range from 89 °C to 124 °C. The molecular ionization energy and electron affinity energy levels in thin films were measured. Photo-induced time of flight (ToF) method was used in to determine charge carrier drift mobilities. It was found out that the formation of deep charge trap states with local energies at approximately 0.60 - 0.78 eV takes place and has a considerable negative effect on the hole drift mobility of the investigated compounds.
关键词： charge transport,molecular glasses,carbazole,organic photovoltaics,azobenzene dyes
更新于2025-09-04 15:30:14
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The Effect of Charge Transport Mechanisms on the Efficiency of AlxGa1 – xAs/GaAs Photodiodes
摘要： Photovoltaic characteristics of heterostructure AlxGa1 – xAs/GaAs p–i–n photodiodes fabricated by molecular-beam epitaxy have been studied. Efficiencies of 50% were reached in conversion of monochromatic light in the photovoltaic mode at power density of up to 200 W/cm2 at a wavelength λ = 830 nm. A relationship was demonstrated between the “saturation currents” for the diffusion-related charge-transport mechanism (Shockley) in p–i–n photodiodes, calculated from dark current–voltage characteristics, and the experimental values of efficiency. As the “saturation current” of the diffusion-related charge-transport mechanism increases by an order of magnitude, a relative decrease in the efficiency from the maximum value by more than 10% is observed under excitation by constant or pulsed monochromatic light.
关键词： efficiency,charge transport mechanisms,molecular-beam epitaxy,photodiodes,AlxGa1 – xAs/GaAs
更新于2025-09-04 15:30:14
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Polymer morphology and interfacial charge transfer dominate over energy-dependent scattering in organic-inorganic thermoelectrics
摘要： Hybrid (organic-inorganic) materials have emerged as a promising class of thermoelectric materials, achieving power factors (S2σ) exceeding those of either constituent. The mechanism of this enhancement is still under debate, and pinpointing the underlying physics has proven dif?cult. In this work, we combine transport measurements with theoretical simulations and ?rst principles calculations on a prototypical PEDOT:PSS-Te(Cux) nanowire hybrid material system to understand the effect of templating and charge redistribution on the thermoelectric performance. Further, we apply the recently developed Kang-Snyder charge transport model to show that scattering of holes in the hybrid system, de?ned by the energy-dependent scattering parameter, remains the same as in the host polymer matrix; performance is instead dictated by polymer morphology manifested in an energy-independent transport coef?cient. We build upon this language to explain thermoelectric behavior in a variety of PEDOT and P3HT based hybrids acting as a guide for future work in multiphase materials.
关键词： polymer morphology,charge transport,PEDOT:PSS,thermoelectric materials,hybrid materials
更新于2025-09-04 15:30:14
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Charge transport layers manage mobility and Carrier density balance in light-emitting layers influencing the operational stability of organic light emitting diodes
摘要： Organic light emitting diodes (OLEDs) consist of several organic layers, including the charge injection layer, charge transport layer, and light emitting layer (EML). Of these layers, the charge transport layer is crucial for ensuring device longevity, but its overall effects on charge transport and corresponding device stability are poorly understood. Herein we report the factors influencing differences in lifetime between two OLEDs with different hole transporting layers (HTLs). Comprehensive electrical analysis of the materials and the devices reveals that the mobility, accumulation, trapping, and the transport path of holes in the EML are totally changed by the HTLs. The charge transport layers affect mobility and carrier density balance in the EML through the modification of the charge transport path and the energetic barrier. This results in a reduction of overbalanced polaron density, which is critical for bond dissociation in excitonic interactions. Consequently, device lifetime is increased sevenfold through modification of the HTL structure without any alteration of the EML. These results imply that the analysis of polaronic transport through impedance spectroscopy is a crucial step in determining the requisite electrical properties for charge transport layers, with a view to maximizing the operational stability of OLEDs.
关键词： charge transport,Organic light-emitting diodes,device stability,impedance spectroscopy
更新于2025-09-04 15:30:14
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Solid-state order and charge mobility in [5]-[12] cycloparaphenylenes
摘要： We report a computational study of mesoscale morphology and charge transport properties of radially π-conjugated cycloparaphenylenes [n]CPPs of various ring sizes (n = 5-12, where n is the number of repeating phenyl units). These molecules are considered as structural constituents of fullerenes and carbon nanotubes. [n]CPP molecules are nested in a unique fashion in the solid state. Molecular dynamics simulations show that while intramolecular structural stability (order) increases with system size, intermolecular structural stability reduces. Density functional calculations reveal that reorganization energy, an important parameter in charge transfer, decreases as n is increased. Intermolecular charge-transfer electronic couplings in the solid state are relatively weak (due to curved π-conjugation and loose intermolecular contacts) and are on the same order of magnitude (i.e., ~10 meV) for each system. Intrinsic charge-carrier mobilities were simulated from kinetic Monte Carlo simulations; hole mobilities increased with system size and scaled as ~n4. We predict that disordered [n]CPPs exhibit hole mobilities as high as 2 cm2/Vs. A strong correlation between reorganization energy and hole mobility, i.e. μ~λ?4, was computed. Quantum mechanical calculations were performed on co-facially stacked molecular pairs for varying phenyl units and revealed that orbital delocalization is responsible for both decreasing reorganization energies and electronic couplings as n is increased.
关键词： kinetic Monte Carlo simulations,charge transport,density functional calculations,molecular dynamics,cycloparaphenylenes
更新于2025-09-04 15:30:14
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Electric field modified Arrhenius description of charge transport in amorphous oxide semiconductor thin film transistors
摘要： While it is known that the charge-carrier mobility in amorphous metal oxide semiconductor thin ?lm transistors (TFT) deviates from Arrhenius temperature dependence, we found that the Hall mobility measured in amorphous In-Ga-Zn-O (a-IGZO) follows an Arrhenius relation surprisingly well. We explain these observations by the effect of strong vertical electric ?eld created by the gate voltage, which facilitates direct tunneling of trapped carriers into the conductive band and leads to virtually temperature independent mobility. We present a generalized Arrhenius model based on the effective temperature concept. We show that our model allows quantitative description of the temperature dependence of the mobility in a-IGZO TFTs over a broad temperature range.
关键词： charge transport,thin film transistors,Arrhenius relation,amorphous oxide semiconductor,electric field
更新于2025-09-04 15:30:14
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Machine Learning-Based Charge Transport Computation for Pentacene
摘要： Insight into the relation between morphology and transport properties of organic semiconductors can be gained using multiscale simulations. Since computing electronic properties, such as the intermolecular transfer integral, using quantum chemical (QC) methods requires a high computational cost, existing models assume several approximations. A machine learning (ML)–based multiscale approach is presented that allows to simulate charge transport in organic semiconductors considering the static disorder within disordered crystals. By mapping ?ngerprints of dimers to their respective transfer integral, a kernel ridge regression ML algorithm for the prediction of charge transfer integrals is trained and evaluated. Since QC calculations of the electronic structure must be performed only once, the use of ML reduces the computation time radically, while maintaining the prediction error small. Transfer integrals predicted by ML are utilized for the computation of charge carrier mobilities using o?-lattice kinetic Monte Carlo (kMC) simulations. Bene?ting from the rapid performance of ML, microscopic processes can be described accurately without the need for phenomenological approximations. The multiscale system is tested with the well-known molecular semiconductor pentacene. The presented methodology allows reproducing the experimentally observed anisotropy of the mobility and enables a fast estimation of the impact of disorder.
关键词： machine learning,multiscale approach,organic semiconductors,charge transport,pentacene
更新于2025-09-04 15:30:14