Conductivity Of Semiconductors Research Articles

Conductivity of two-dimensional narrow gap semiconductors subjected to strong Coulomb disorder

In the ideal disorder-free situation, a two-dimensional band-gap insulator has an activation energy for conductivity equal to half the band gap $\mathrm{\ensuremath{\Delta}}$. But transport experiments usually exhibit a much smaller activation energy at low temperature, and the relation between this activation energy and $\mathrm{\ensuremath{\Delta}}$ is unclear. Here we consider the temperature-dependent conductivity of a two-dimensional insulator on a substrate containing Coulomb impurities, with random potential amplitude $\mathrm{\ensuremath{\Gamma}}\ensuremath{\gg}\mathrm{\ensuremath{\Delta}}$. We show that the conductivity generically exhibits three regimes of conductivity, and only the highest-temperature regime exhibits an activation energy that reflects the band gap. At lower temperatures, the conduction proceeds through activated hopping or Efros-Shklovskii variable-range hopping between electron and hole puddles created by the disorder. We show that the activation energy and characteristic temperature associated with these processes steeply collapse near a critical impurity concentration. Larger concentrations lead to an exponentially small activation energy and exponentially long localization length, which in mesoscopic samples can appear as a disorder-induced insulator-to-metal transition. We also arrive at a similar steep disorder driven insulator-metal transition in thin films of three-dimensional topological insulators with large dielectric constant, for which Coulomb impurities inside the film create a large disorder potential due to confinement of their electric field inside the film.

Delocalization Enhances Conductivity at High Doping Concentrations

AbstractMany applications of organic semiconductors require high electrical conductivities and hence high doping levels. Therefore, it is indispensable for effective material design to have an accurate understanding of the underlying transport mechanisms in this regime. In this study, own and literature experimental data that reveal a power‐law relation between the conductivity and charge density of strongly p‐doped conjugated polymers are combined. This behavior cannot consistently be described with conventional models for charge transport in energetically disordered materials. Here, it is shown that the observations can be explained in terms of a variable range hopping model with an energy‐dependent localization length. A tight‐binding model is used to quantitatively estimate of the energy‐dependent localization length, which is used in an analytical variable range hopping model. In the limit of low charge densities, the model reproduces the well‐known Mott variable range hopping behavior, while for high charge densities, the experimentally observed superlinear increase in conductivity with charge density is reproduced. The latter behavior occurs when the Fermi level reaches partially delocalized states. This insight can be anticipated to lead to new strategies to increase the conductivity of organic semiconductors.

Capacitive characteristics and electrosorption of hydrogen in microporous aсtivated carbon fibers

The possibility of hydrogen electrosorption in microporous activated carbons for acidic and alkaline electrolytes is shown. The electrochemical behavior of activated carbon fiber CH-900-20 has been investigated to find out the main factors, which influence the charging processes of microporous electrodes. The following methods were used: cyclic voltammetry, electrochemical impedance spectroscopy, chronoamperometry, and chronopotentiometry. A comparative analysis of the influence of the electrolyte type and electrode structure on the capacitance performances of carbon has been carried out. It is assumed that there is a potential barrier at the interface between micropores and macropores. The features of the process of hydrogen electrosorption in carbon micropores have been analyzed in detail. A possible mechanism of electrosorption in micropores that decreases the capacitance of the electric double layer with a corresponding drop of the electronic conductance of activated carbons in acidic electrolytes has been suggested. The influence of temperature on the kinetics of hydrogen electrosorption has been shown and the activation energy of this process has been estimated. An assumption has been made about the influence of the semiconductor conductivity of activated carbons on the capacitive and resistive characteristics of the electrodes. • The capacitance characteristics of microporous carbon fiber in alkaline and acidic electrolytes are compared. • The possibility of hydrogen electrosorption in micropores of activated carbons for acidic media is shown. • The characteristics of the electrodes made of pre-dispersed powder and the initial activated carbon fiber are compared.

Organometallic and Organic Dimers: Moderately Air-Stable, Yet Highly Reducing, n-Dopants.

ConspectusElectrical doping using redox-active molecules can increase the conductivity of organic semiconductors and lower charge-carrier injection and extraction barriers; it has application in devices such as organic and perovskite light-emitting diodes, organic and perovskite photovoltaic cells, field-effect transistors, and thermoelectric devices. Simple one-electron reductants that can act as n-dopants for a wide range of useful semiconductors must necessarily have low ionization energies and are, thus, highly sensitive toward ambient conditions, leading to challenges in their storage and handling. A number of approaches to this challenge have been developed, in which the highly reducing species is generated from a precursor or in which electron transfer is coupled in some way to a chemical reaction. Many of these approaches are relatively limited in applicability because of processing constraints, limited dopant strength, or the formation of side products.This Account discusses our work to develop relatively stable, yet highly reducing, n-dopants based on the dimers formed by some 19-electron organometallic complexes and by some organic radicals. These dimers are sufficiently inert that they can be briefly handled as solids in air but react with acceptors to release two electrons and to form two equivalents of stable monomeric cations, without formation of unwanted side products. We first discuss syntheses of such dimers, both previously reported and our own. We next turn to discuss their thermodynamic redox potentials, which depend on both the oxidation potential of the highly reducing odd-electron monomers and on the free energies of dissociation of the dimers; because trends in both these quantities depend on the monomer stability, they often more-or-less cancel, resulting in effective redox potentials for a number of the organometallic dimers that are approximately -2.0 V vs ferrocenium/ferrocene. However, variations in the dimer oxidation potential and the dissociation energies determine the mechanism through which a dimer reacts with a given acceptor in solution: in all cases dimer-to-acceptor electron transfer is followed by dimer cation cleavage and a subsequent second electron transfer from the neutral monomer to the acceptor, but examples with weak central bonds can also react through endergonic cleavage of the neutral dimer, followed by electron-transfer reactions between the resulting monomers and the acceptor. We, then, discuss the use of these dimers to dope a wide range of semiconductors through both vacuum and solution processing. In particular, we highlight the role of photoactivation in extending the reach of one of these dopants, enabling successful doping of a low-electron-affinity electron-transport material in an organic light-emitting diode. Finally, we suggest future directions for research using dimeric dopants.

Study of interfacial design for direct-current tribovoltaic generators

As a newly discovered physical phenomenon, tribovoltaic effect has potential applications in various fields. Herein, we systematically study the relationship between interfacial properties of the tribovoltaic generator and its output performance using a conductor-semiconductor (C-S) structure. Based on several similar physical models, we derive an equation to quantify the effects of contact area, load force and the density of surface states of the semiconductor on performance of the tribovoltaic generator. The experimental results are in good agreements with the theoretical analysis. Moreover, the contribution of interfacial electric field and interfacial magnetic field to the tribovoltaic effect are discussed, respectively. By using epitaxial silicon (Si) film, the built-in electric field near the C-S interface can be regulated, which leads to suppression of the recombination effect of the tribovoltaic charges, and the short-circuit current of the tribovoltaic generator can be increased by 66.83%. This work paves the way for electrode design and better output performance of flexible DC tribovoltaic generator in the future.

Максимальная прыжковая электропроводность на постоянном токе по водородоподобным примесям в полупроводниках

A quasi-classical model for calculating DC (direct current) electrical conductivity in crystalline semiconductors with hydrogen-like impurities is developed at the transition from band conduction to impurity hopping conduction with decreasing temperature. This transition from the minimum band conductivity to the maximum hopping conductivity via impurities has the form of a characteristic ``kink'' in the temperature dependence of the electrical resistivity. The idea of the calculation is to preliminarily determine the transition temperature Tj using the standard approach within the framework of the two-band model. The shift of the top of the v-band (the bottom of the c-band) into the depth of the band gap due to the formation of a quasi-continuous band of allowed energy values from the excited states of acceptors (donors) is taken into account. This leads to a decrease in the value of a thermal ionization energy of the main shallow impurities due to a decrease in the maximum localization radius of a hole on an acceptor (an electron on a donor) with increasing impurity concentration. The values of the observed maximum hopping conductivity and drift hopping mobility corresponding to the temperature Tj are calculated. The numerical calculation within the framework of the proposed model is consistent with the known experimental data on the electrical conductivity and Hall coefficient of moderately compensated p-Ge crystals doped by neutron transmutation and non-intentionally compensated metallurgically doped n-Ge, as well as n- and p-Si crystals on the insulator side of the Mott insulator–metal concentration phase transition.

Solvent-controlled ion-coupled charge transport in microporous metal chalcogenides.

Interactions between ions and itinerant charges govern electronic processes ranging from the redox chemistry of molecules to the conductivity of organic semiconductors, but remain an open frontier in the study of microporous materials. These interactions may strongly influence the electronic behavior of microporous materials that confine ions and charges to length scales comparable to proton-coupled electron transfer. Yet despite mounting evidence that both solvent and electrolyte influence charge transport through ion-charge interactions in metal-organic frameworks, fundamental microscopic insights are only just beginning to emerge. Here, through electrochemical analysis of two open-framework chalcogenides TMA2FeGe4S10 and TMA2ZnGe4S10, we outline the key signatures of ion-coupled charge transport in band-type and hopping-type microporous conductors. Pressed-pellet direct-current and impedance techniques reveal that solvent enhances the conductivity of both materials, but for distinct mechanistic reasons. This analysis required the development of a fitting method that provides a novel quantitative metric of concerted ion-charge motion. Taken together, these results provide chemical parameters for a general understanding of electrochemistry in nanoconfined spaces and for designing microporous conductors and electrochemical methods used to evaluate them.

Maximum hopping direct current conductivity via hydrogen-like impurities in semiconductors

A quasi-classical model for calculating DC (direct current) electrical conductivity in crystalline semiconductors with hydrogen-like impurities is developed at the transition from band conduction to impurity hopping conduction with decreasing temperature. This transition from the minimum band conductivity to the maximum hopping conductivity via impurities has the form of a characteristic "kink" in the temperature dependence of the electrical resistivity. The idea of the calculation is to preliminarily determine the transition temperature Tj using the standard approach within the framework of the two-band model. The shift of the top of the v-band (the bottom of the c-band) into the depth of the band gap due to the formation of a quasi-continuous band of allowed energy values from the excited states of acceptors (donors) is taken into account. This leads to a decrease in the value of a thermal ionization energy of the majority shallow impurities due to a decrease in the maximum localization radius of a hole on an acceptor (an electron on a donor) with increasing impurity concentration. The values of the observed maximum hopping conductivity and drift hopping mobility corresponding to the temperature Tj are calculated. The numerical calculation within the framework of the proposed model is consistent with the known experimental data on the electrical conductivity and Hall coefficient of moderately compensated p-Ge crystals doped by neutron transmutation and non-intentionally compensated metallurgically doped n-Ge, as well as n- and p-Si crystals on the insulator side of the Mott insulator--metal concentration phase transition. Keywords: bulk crystals of germanium and silicon, hydrogen-like acceptors and donors, holes and electrons, band and hopping motion of charge carriers.

Backbone-driven host-dopant miscibility modulates molecular doping in NDI conjugated polymers.

Molecular doping is the key to enabling organic electronic devices, however, the design strategies to maximize doping efficiency demands further clarity and comprehension. Previous reports focus on the effect of the side chains, but the role of the backbone is still not well understood. In this study, we synthesize a series of NDI-based copolymers with bithiophene, vinylene, and acetylenic moieties (P1G, P2G, and P3G, respectively), all containing branched triethylene glycol side chains. Using computational and experimental methods, we explore the impact of the conjugated backbone using three key parameters for doping in organic semiconductors: energy levels, microstructure, and miscibility. Our experimental results show that P1G undergoes the most efficient n-type doping owed primarily to its higher dipole moment, and better host–dopant miscibility with N-DMBI. In contrast, P2G and P3G possess more planar backbones than P1G, but the lack of long-range order, and poor host–dopant miscibility limit their doping efficiency. Our data suggest that backbone planarity alone is not enough to maximize the electrical conductivity (σ) of n-type doped organic semiconductors, and that backbone polarity also plays an important role in enhancing σ via host–dopant miscibility. Finally, the thermoelectric properties of doped P1G exhibit a power factor of 0.077 μW m−1 K−2, and ultra-low in-plane thermal conductivity of 0.13 W m−1K−1 at 5 mol% of N-DMBI, which is among the lowest thermal conductivity values reported for n-type doped conjugated polymers.

Influence of external factors on the electrical conductivity of Bi2Te2.5Se0.5

The mechanism of intrinsic and impurity electrical conductivity of semiconductors based on Bi2Te2.5Se0.5 has been elucidated. The nature and reasons for the dependence of electrical conductivity on various external influences are considered. In this case, the temperature dependence of electrical conductivity, light absorption and photoconductivity of Bi2Te2.5Se0.5 were used as external influences. And also the influence of the electric field was studied and it was found that in this case the value of the critical energy is 107V/m.

First-principles study on optoelectronic properties of new quinacridone dye derivatives in dye sensitized photovoltaic cells

In this work, we design new organic dyes for dye sensitized photovoltaic cells (DSPVs). We use density functional theory (DFT) and time dependent-density functional theory (TD-DFT) calculations to study the novel dyes based quinacridone derivatives (A1-A8). In particular, we examine the molecular orbitals distributions, absorption proprieties, light collection efficiency, injection driving force, electronic vertical excitation energy and oscillator forces. We reveal that all designed molecules have a low band gap and excellent optical properties. In addition, we investigate the photovoltaic performance of new dyes. Therefore, the engineered dyes present a potential effective electron injection into the semiconductor conduction band. The achieved outcomes motivate the scientific committees to investigate such molecules experimentally, that might improve the efficiency of dye sensitized photovoltaic cells (DSPVs).

Поляризационные процессы в пленках йодида серебра вблизи температуры суперионного фазового перехода

The article reports the results of dielectric spectroscopy analysis exploring polarization processes in silver iodide nanocrystalline films in the region of thermal superionic phase transition. It also provides calculations of the system’s relaxation and energy parameters. The abrupt change of parameters at the transition point is demonstrated by activation energy of semiconductor conduction and commit phases, indicator of the degree of frequency dependence of conductivity, and the maximum value of the function of the tangent of the dielectric loss angle. The article proposes a model of the micro-mechanism of the thermal phase transition from a semiconductor to a superionic state. It is shown that, along with the superionic phase transition, films undergo a percolation phase transition with the formation of a two-dimensional percolation cluster.

Local structure analysis of Sb, Bi, and Ag dopant atoms in Mg2Si semiconductor by x-ray absorption spectroscopy and first-principles calculation

The local structures around Sb, Bi, and Ag dopant atoms in the environmentally friendly semiconductor Mg2Si were investigated by Sb K-edge, Bi L3-edge, and Ag K-edge x-ray absorption spectroscopy performed at 10 K. Fourier transforms (FTs) of the k3-weighted extended x-ray absorption fine structure (EXAFS) were analyzed. The experimental FTs of k3-weighted EXAFS were compared with the results of calculations using model clusters with Sb, Bi, and Ag atoms at the 8c, 4a, and 4b sites. The inverse FT of the χ(R) spectrum was calculated to refine the local structures for neighboring atoms around the Sb, Bi, and Ag atoms, and the interatomic distances and Debye–Waller factors were determined from the fit of the inverse FTs. The occupation of the 4a site by Sb and Bi atoms was demonstrated and that of the 8c site was investigated for Ag atoms. First-principles calculations were performed to clarify the characteristic change in the second-neighbor distances around the Ag atoms. The evaluation of the crystal orbital Hamilton population clarified that the change in the second-neighbor distances is caused by the bonding character formed between the Ag and Mg atoms. These results suggest that the Ag atoms mainly occupy the 8c site, while the large value of the Debye–Waller factor for the second neighboring atoms implies the possibility of the partial occupation of Ag atoms at the 4b sites. These findings provide an explanation for limiting the p-type conductivity in Mg2Si semiconductors.

Temperative Dependence of Electrical Conductivity in Semiconductors

The electrical conductivity of a semiconductor material is between that of a conductor, such as metallic copper, and that of an insulator, such as glass. Its resistivity decreases as the temperature rises, whereas metals have the reverse effect. By adding impurities ("doping") into the crystal structure, its conducting characteristics can be changed in beneficial ways. A semiconductor junction is formed when two differentially doped areas in the same crystal occur. Diodes, transistors, and most contemporary electronics are built on the behavior of charge carriers such as electrons, ions, and electron holes at these junctions. Silicon, germanium, gallium arsenide, and elements near the periodic table's "metalloid staircase" are examples of semiconductors. Gallium arsenide is the second most common semiconductor after silicon, and it's utilized in things like laser diodes, solar cells, and microwave-frequency integrated circuits. Silicon is a crucial component in the production of most electrical circuits. The electrical conductivity of semiconductors varies significantly with temperature. It acts as an insulator at absolute zero. Some of the semiconductor's covalent bonds disintegrate at room temperature due to thermal energy.

Lattice Thermal Transport in the Homogeneous Cage‐Like Compounds Cu3VSe4 and Cu3NbSe4: Interplay between Phonon‐Phase Space, Anharmonicity, and Atomic Mass

AbstractUnderstanding the correlation between crystal structure and thermal conductivity in semiconductors is very important for designing heat‐transport‐related devices, such as high‐performance thermoelectric materials and heat dissipation in micro‐nano‐scale devices. In this work, the lattice thermal conductivity ( ) of the cage‐like compounds Cu3VSe4 and Cu3NbSe4 was investigated by experimental measurements and first‐principles calculations. The experimental of Cu3NbSe4 is approximately 25 % lower than that of Cu3VSe4 at 300 K. The relevant important physical parameters, including the sound velocity, heat capacity, weighted phonon phase space (W), and third‐order force constants along with atomic mass were theoretically analyzed. It is found that W is the dominant parameter in determining the , and the other factors only play a minor role. The physical origin is the relatively “soft” lattice of Cu3NbSe4 with heavier atomic mass. This research provides deep insight into the correlation between the thermal conductivity and crystal structure and paves the way for discovering high‐performance thermal management device and thermoelectric materials with intrinsically low .

Thermal transport in organic semiconductors

Organic semiconductors have attracted worldwide attention and have shown great potential in emerging organic electronic devices due to their excellent properties. Advances in miniaturization and integration of organic electronic devices require understanding and tuning thermal transport capabilities of organic semiconductors to achieve desired results. In this Perspective, recent advances in the thermal transport of organic semiconductors are summarized and discussed. First, the characteristics and applications of organic semiconductors are systematically introduced. In addition, thermal conductivities of organic semiconductors and interfacial thermal conductances of different organic semiconductor-based interfaces are analyzed and summarized, respectively. Moreover, thermoelectric applications of organic semiconductors are discussed. Finally, this Perspective concludes with a summary of the current research and an outlook to guide future research in the field of organic semiconductors.

Thermal transport in semiconductors studied by Monte Carlo simulations combined with the Green-Kubo formalism

In this paper, we demonstrate that it is possible to combine two computational approaches, usually used in very different contexts, namely, the Green-Kubo formalism and statistical approaches, to solve the Boltzmann transport equation to calculate the thermal conductivity of semiconductors. In this framework, first the phonon transport is solved by the Monte Carlo method according to the Debye-Callaway or Holland formalisms, then the flux autocorrelation is calculated. This new approach has been implemented to calculate the properties of Si, Ge, GaN, and C (diamond) in an extended temperature range, from 50 to 600 K. The simulation results are compared with those given by experimentation, with very good agreement.

Computational analysis of novel high performance optically controlled RF switches for reconfigurable millimeterwave-to-THz circuits

Optically controlled RF switches with a novel non-contact device architecture that achieves high performance in the millimeterwave-to-terahertz (mmW-THz) region are proposed and investigated through simulation. The significant change in conductivity in semiconductors caused by photogenerated carriers is used to develop RF switches having very high performance. By including a thin layer of insulator between the active semiconductor material and the metal contacts, the carrier concentration can be enhanced over that of conventional devices. For a prototype demonstration, G-band coplanar waveguide-based optical switches (using Si and Ge as active materials) with different contact geometries have been modeled and simulated. The proposed switches outperform both conventional solid-state switches and phase-change material-based switches in the switch figure-of-merit, and are promising for developing a novel class of tunable and reconfigurable mmW-THz circuits for advanced sensing, imaging, and communication.

Calculation of the temperature behavior features of electrical conductivity in GeTe, SnTe and A(x–1) B(x) C semiconductors – solutions of Tc near-structural phase transition

Temperature behavior calculation of the anomalous conductivity of the A4B6-type ferroelectric semiconductors (GeTe, SnTe and A(x–1) B(x)C) of Tc near-phase transitions is carried out in the paper. The proposed integrable (analytical) model is applicable both for describing the temperature behavior of the conductivity of GeTe multivalley semiconductors and SnTe-type systems. The influence of the structural phase transition on the systems’ conductivity is analyzed. The proposed analytical model of the conductivity behavior of ferroelectrics-semiconductors allows considering compounds with various spectra and compositions. The model is applicable both for the kinetic properties of multivalley semiconductors and for analyzing the effect of external influences on these properties: x composition and T temperature, as well as the presence of a structural phase transition in the system at Tc(x). It is shown that the graph can have the form of a break or the form of a smooth asymmetric maximum, depending on the value of the effective relaxation rate of carriers on soft phonons and the intervalley splitting of the anomalous conductivity near Tc in A4B6 systems. The calculation results are consistent with the experimental data. The dependence of the phase transition temperature Tc(x) on x composition is obtained.

Liquid Metal Particles and Polymers: A Soft–Soft System with Exciting Properties

ConspectusGallium-based liquid metal alloys are a special type of material that is in the liquid state at (or near) room temperature. They are particularly attractive due to their unique combination of a fluidic and metallic body, together with a chemically reactive and functionable surface. As a fluid, liquid metals provide the best union of stretchability, deformability, and electrical conductivity among all soft materials. Such an advantage in combination with their low toxicity and relatively good biocompatibility have imparted liquid metals with unique features that can be harnessed for versatile applications in fields such as electronics, energy, chemistry, and biomedical research. More importantly, the fluidic nature of liquid metals allows them to be readily processed using shear for making particles with variable sizes (from nm to mm), which is not possible with solid materials. These particles have a liquid metal core–solid metal oxide shell (conductor–semiconductor) structure, allowing them to merge, transform shape, change phase, respond to stimuli, and self-heal.Despite these unique features, limited surface stability and functionality, unpredictable reactivity, and uncontrollable hydrophilicity of liquid metal particles niche their wider applications in biomedical fields. To bestow liquid metal particles with desirable surface properties while taking the benefits offered by soft features, another important soft material—polymers—can be synthesized and engineered on an on-demand basis to coat or embed liquid metal particles. This leads to the formation of liquid metal–polymer soft composites with versatile surface properties. More specifically, polymer segments with corresponding functions for surface anchoring, tuning solubility, enhancing biocompatibility, providing stimuli-responsive properties, and further bioconjugation can be linked together, thereby forming macromolecules to graft liquid metal particles for yielding soft–soft systems with exciting properties.Herein, we provide a concise review of our contributions to the production, investigation, characterization, and application of liquid metal particle–polymer composites. First, we summarize various top-down techniques developed for producing micro- to nanosized liquid metal particles. We highlight two platforms we developed for tackling long-existing problems encountered by sonication—the most widely adopted method for producing liquid metal particles. Second, we discuss the design of polymers for surface modification of particles. Various grafting strategies for polymers synthesized using different approaches are elaborated. We also discuss factors that affect the colloidal and chemical stability of the composite in biological buffers. Methods for further surface functionalization of the composite are presented, followed by providing examples of biomedical and sensing applications for the system. Next, we introduce the fabrication, unique properties, and applications of elastomeric hybrid composites incorporating liquid metal particle fillers. Finally, we offer a perspective on the opportunities and challenges for the future development of this exciting soft–soft system for realizing synergistic outcomes.