Meyer Neldel Research Articles

Observation of temperature-dependent capture cross section for main deep-levels in β-Ga2O3

Direct observation of the capture cross section is challenging due to the need for extremely short filling pulses in the two-gate Deep-Level Transient Spectroscopy (DLTS). Simple estimation of the cross section can be done from DLTS and admittance spectroscopy data but it is not feasible to distinguish temperature dependence of pre-exponential and exponential parts of the emission rate equation with sufficient precision conducting a single experiment. This paper presents experimental data of deep levels in β-Ga2O3 that has been gathered by our group since 2017. Based on the gathered data, we propose a derivation of apparent activation energy (Eam) and capture cross section (σnm) assuming the temperature dependent capture via the multiphonon emission model, which resulted in a strong correlation between Eam and σnm according to the Meyer–Neldel rule, which allowed us to estimate low- and high-temperature capture coefficients C0 and C1 as well as capture barrier Eb. It also has been shown that without considering the temperature dependence of capture cross section, the experimental values of σn are overestimated by 1–3 orders of magnitude. A careful consideration of the data also allows to be more certain identifying deep levels by their “fingerprints” (Ea and σn) considering two additional parameters (EMN and σ00) and to verify the density functional theory computation of deep-level recombination properties.

Low-temperature electrical conductivity of ion-beam irradiated Bi–Sb films

Bismuth-antimony alloys are among the most studied topological insulators and also have very promising thermoelectric properties. In addition, in the amorphous state they exhibit superconductivity with critical temperatures in the range 6.0–6.4 K. In this work, we have prepared and studied different polycrystalline films of Bi100–xSbx (x = 0, 5, 10, 15), and we have induced, through ion beam irradiation, significant damage in their internal structure with the aim of amorphizing the material. Specifically, we have irradiated Bi ions in the 10–30 MeV range, exploiting the capabilities of a 5 MV ion beam accelerator of tandem type. We have characterized the Bi–Sb films before and after irradiation from a morphological and structural point of view and measured their electrical resistivity from room temperature to near 2 K, to evaluate the influence of the preparation method and degree of disorder. We have found that the studied Bi–Sb system always behaves as a small energy gap semiconductor that follows the empirical Meyer–Neldel rule, which correlates the conductivity prefactor with the exponential value of the energy gap.

Empirical universal approach to describing the thermal conductivity of amorphous polymers: Effects of pressure, radiation and the Meyer–Neldel rule

In this study, we propose and validate a universal temperature-dependent model for characterizing the thermal conductivity of amorphous polymers over a wide temperature range. Our approach captures key features in the thermal conductivity data, including a plateau, an inflection point, and the subsequent increase and saturation with rising temperature. Importantly, this model proves effective not only for pristine amorphous polymers but also for polymers subjected to external influences. We investigate the temperature-dependent thermal conductivity of amorphous polymer materials under various external conditions, such as hydrostatic pressure, radiation exposure, and the incorporation of fillers. Our analysis reveals novel insights into the dual-channel heat transfer mechanisms within amorphous polymers. Specifically, we observe a linear relationship between the logarithm of the “coherence” conductivity pre-factor and the characteristic energy, consistent with the Meyer–Neldel rule governing thermal conductivity. This research advances our understanding of thermal transport in amorphous polymers and underscores the applicability of the proposed universal model in describing complex thermal behavior across different conditions.

Structural Study, Observation of Non-Ohmic I–V Characteristics and Analysis of Meyer–Neldel Rule in Sb-Additive Se-Te-Ge Quaternary Amorphous Alloys

Structural Study, Observation of Non-Ohmic I–V Characteristics and Analysis of Meyer–Neldel Rule in Sb-Additive Se-Te-Ge Quaternary Amorphous Alloys

Voltage deficit in PV with suppressed recombination

The observed open circuit voltages in best performing solar cells are explained outside of the recombination paradigm, based on such factors as electrostatic screening, Meyer–Neldel effect, and lateral nonuniformities. The underlying concept of suppressed recombination presents a long neglected alternative pathway to efficient photovoltaic. The criteria of suppressed recombination and effective charge carrier extraction are consistent with the data for best performing solar cells.

Analyzing Acceptor-like State Distribution of Solution-Processed Indium-Zinc-Oxide Semiconductor Depending on the In Concentration.

Understanding the density of state (DOS) distribution in solution-processed indium-zinc-oxide (IZO) thin-film transistors (TFTs) is crucial for addressing electrical instability. This paper presents quantitative calculations of the acceptor-like state distribution of solution-processed IZO TFTs using thermal energy analysis. To extract the acceptor-like state distribution, the electrical characteristics of IZO TFTs with various In molarity ratios were analyzed with respect to temperature. An Arrhenius plot was used to determine electrical parameters such as the activation energy, flat band energy, and flat band voltage. Two calculation methods, the simplified charge approximation and the Meyer-Neldel (MN) rule-based carrier-surface potential field-effect analysis, were proposed to estimate the acceptor-like state distribution. The simplified charge approximation established the modeling of acceptor-like states using the charge-voltage relationship. The MN rule-based field-effect analysis validated the DOS distribution through the carrier-surface potential relationship. In addition, this study introduces practical and effective approaches for determining the DOS distribution of solution-processed IZO semiconductors based on the In molarity ratio. The profiles of the acceptor-like state distribution provide insights into the electrical behavior depending on the doping concentration of the solution-processed IZO semiconductors.

Effect of structure on semiconducting properties of a small molecule n-type organic semiconductor: Phenyl-C61-butyric acid methyl ester

The fullerene-based derivative phenyl-C61-butyric acid methyl ester (PCBM) has attracted attention as an n-type transistor channel and an organic photovoltaic material due to its solution processability, stability, and high electron mobility. However, disorder in solution-processed PCBM thin films makes understanding of charge carrier transport mechanisms difficult. We have fabricated PCBM-based field effect transistors and improved device performance by reducing electron trapping at the dielectric–semiconductor interface and improving charge carrier injection. Single-wall carbon nanotubes were successfully integrated into conventional gold electrodes to improve injection efficiency. Meyer–Neldel behavior has been investigated in a study of charge carrier transport in PCBM thin films. Crystallization of PCBM was observed during the measurement. We find that charge carriers hop between molecules in mostly amorphous regions from 145 to 240 K. The transport is facilitated by the formation of more crystallized regions when samples are heated as high as 240 K.

Impedance spectroscopy and conduction mechanism analysis of bulk nanostructure Prussian blue pellets

The structure and morphology of the fabricated Prussian Blue (PB) pellets are examined using FTIR, XPS, XRD and FESEM techniques. The morphology of the crystalline Prussian blue (PB) revealed a nanostructure with an average crystallite size of 91 nm. The frequency (42 Hz–1 MHz) and temperature (303–393K) of the Prussian Blue (PB) in Bulk form are dependent. In the medium region (1 kHz–100 kHz), the electric dipoles relax and start to lag the applied ac electric field signal and the estimated activation energy of 0.247 eV. The investigated Nyquist plots (Z″ versus Z′) of the Prussian Blue (PB) samples at different temperatures (303–393 K) are interpreted by an equivalent parallel RgCg circuit. The bulk resistance of Prussian Blue samples was estimated at various temperatures, and its behaviour exhibited temperature dependence; generally, it follows the Nearest Neighbor Hopping (NNH) model. According to Meyer–Neldel rule, the calculated activation energy is 0.565 ± 0.001 eV. The evidence of localized states is investigated, and its density, N(EF) ∼ 5.47 × 1018 eV−1 cm−3. The ac conductivity, σac, merges into a plateau of two parts: the first is a frequency-independent dc conductivity, σdc, which is strongly temperature-dependent. The rest of the plateau at higher frequencies showed the temperature-insensitive ac conductivity obeying Jonscher's power law. The values of the exponent s were investigated to figure out the intimate conduction mechanism in Prussian Blue (PB) samples; it follows the correlated barrier hopping (CBH) theoretical model. The hopping distance and energy have values ∼ unity and ≥ kBT, respectively. The experimental results revealed a linear relationship between hopping distance and energy against temperature, with the first decreasing and the second increasing linearly.

Comparative study of the exponential-trap-based and the mobility-based space-charge-limited current models for organic diode modeling

Current model is presented for the forward-biased organic diodes. Generally, the diode current consists of two parts: the space-charge-limited current in high-voltage regime and the Ohmic current in low-voltage regime. The two classical space-charge-limited current models, i.e., the exponential-trap-based model and the mobility-based model, are analyzed. Their similarity and difference are clarified: they are similar in the form of the Meyer–Neldel rule, but different in the diode thickness. Comparing their calculated results with the available experimental data at different thicknesses, it is found that, the exponential-trap-based model is suitable, and the mobility-based model shows limitation. Moreover, the Ohmic current model is presented considering the temperature and thickness dependence. Combining the exponential-trap-based space-charge-limited current model with the Ohmic current model, the diode current model is achieved. The model is analytical and suitable for circuit simulation, and is verified by the available experimental data at different temperatures and thicknesses.

Electronic transport properties of Ti-supersaturated Si processed by rapid thermal annealing or pulsed-laser melting

In the scope of supersaturated semiconductors for infrared detectors, we implanted Si samples with Ti at high doses and processed them by rapid thermal annealing (RTA) to recover the crystal quality. Also, for comparative purposes, some samples were processed by pulsed-laser melting. We measured the electronic transport properties at variable temperatures and analyzed the results. The results indicate that, for RTA samples, surface layers with a high Ti concentration have negligible conductivity due to defects. In contrast, the implantation tail region has measurable conductivity due to very high electron mobility. This region shows the activation of a very shallow donor and a deep donor level. While deep levels have been previously reported for Ti in Si, such a shallow level has never been measured, and we suggest that it originates from Ti-Si complexes. Finally, a decoupling effect between the implanted layer and the substrate seems to be present, and a bilayer model is applied to fit the measured properties. The fitted parameters follow the Meyer–Neldel rule. The role of the implantation tails in Si supersaturated with Ti is revealed in this work.

Some novel perspectives of iso-conversional analysis in the study of Meyer–Neldel energy for thermally governed crystallization by using Johnson–Mehl–Avrami (JMA) theory

Some novel perspectives of iso-conversional analysis in the study of Meyer–Neldel energy for thermally governed crystallization by using Johnson–Mehl–Avrami (JMA) theory

Considering the Role of Ion Transport in Diffuson‐Dominated Thermal Conductivity

AbstractNext‐generation thermal management requires the development of low lattice thermal conductivity materials, as observed in ionic conductors. For example, thermoelectric efficiency is increased when thermal conductivity is decreased. Detrimentally, high ionic conductivity leads to thermoelectric device degradation. Battery safety and design also require an understanding of thermal transport in ionic conductors. Ion mobility, structural complexity, and anharmonicity have been used to explain the thermal transport properties of ionic conductors. However, thermal and ionic transport are rarely discussed in direct comparison. Herein, the ionic conductivity of Ag+ argyrodites is found to change by orders of magnitude without altering the thermal conductivity. Thermal conductivity measurements and two‐channel lattice dynamics modeling reveal that the majority of Ag+ vibrations have a non‐propagating diffuson‐like character, similar to amorphous materials. It is found that high ionic mobility is not a requirement for diffuson‐mediated transport. Instead, the same bonding and structural traits that can lead to fast ionic conduction also lead to diffuson‐mediated transport. Bridging the fields of solid‐state ionics and thermal transport, it is proposed that a vibrational perspective can lead to new design strategies for functional ionic conducting materials. As a first step, the authors relate the so‐called Meyer–Neldel behavior in ionic conductors to phonon occupations.

AC conductivity and electrical relaxation of a promising Ag2S-Ge-Te-Se chalcogenide glassy system

In this study, we developed a chalcogenide glassy system comprising (Ag2S)x-(0.4Ge-0.3Te-0.3Se)1-x, where x = 0.05, 0.10, and 0.20. The formation of Ag2S and GeSe2 nanocrystallites with small sizes and the development of GeTe, Ag2GeS3, TeS, and Se5.95Te1.05 phases with high Ag2S contents were confirmed by X-ray diffraction. The Fourier transform-infrared spectra demonstrated the characteristic vibration of Ag–S at 500–600 cm−1. Kinetic analysis of conductivity suggested that the Meyer–Neldel energy was due to polarons hopping from trap to trap induced by multiple phonon excitation. Tunneling of polarons through the grain boundary when x = 0.1 could be interpreted based on the modified non-overlapping small polaron tunneling model. By contrast, the correlated barrier hopping model was more appropriate for explaining the dominant conduction mechanism when x = 0.05 and 0.2. The lower relaxation times when x = 0.05 and 0.2 indicated a higher rate of polaron hopping. The temperature independence of the relaxation process was confirmed based on the scaling process.

Highly conducting nanophases of Ag2S–Se-Ge chalcogenide glassy systems: Explanations via computational descriptions

The temperature and frequency dependent AC conductivity of some Ag2S doped chalcogenides is prepared in the laboratory and experimental data have been collected. Its structural analysis is carried out with X-Ray Diffraction and UV–Vis Spectroscopic methods. The estimated values of optical band gap energy, Egare found to increase with Ag2S content and the present system may be classified as allowed indirect band gap semiconductor. The density and molar volume of as-prepared samples have also been estimated. The AC conductivity of this system has been found to obey the Meyer-Neldel (MN) rule. The decrease of Meyer-Neldel characteristic energy EMN with compositions has been observed. Higher conductivity as well as hopping frequency should be caused due to highly conducting Ag2Senanophases, which is confirmed from DFT and Density of States (DOS) spectra.

On the Study of “Further Meyer–Neldel Rule” in Thermally Activated High Field Conduction of Se-Te-Pb Glassy Alloys

On the Study of “Further Meyer–Neldel Rule” in Thermally Activated High Field Conduction of Se-Te-Pb Glassy Alloys

Understanding the effect of lattice polarisability on the electrochemical properties of lithium tetrahaloaluminates, LiAlX4 (X = Cl, Br, I)

Lithium ion conductivity in haloaluminate solid electrolytes can be tuned by the softening of the anion sublattice via a judicious juggling of the migration activation energy, Ea and the Meyer–Neldel energy, Δ0.

Optimizing the Proton Conductivity with the Isokinetic Temperature in Perovskite‐Type Proton Conductors According to Meyer–Neldel Rule

AbstractPerovskite‐type metal oxides such as Y‐doped BaMO3 (M = Zr/Ce) have drawn considerable attention as proton‐conducting electrolytes for intermediate temperature ceramic electrochemical cells. Improving the proton conductivity at lower temperatures requires a comprehensive understanding of the proton conduction mechanism. By applying high pressure or varying the Ce content of Y‐doped BaMO3, it is demonstrated that the proton conductivity follows the Meyer–Neldel rule (MNR) well. In the Arrhenius plot, the conductivities intersect at an isokinetic temperature, where the proton conductivity is independent of activation energy. Considering the relationship between isokinetic temperature and lattice vibration frequency, a high isokinetic temperature is observed in materials with stiff lattices, consisting of light atoms and small MO bond length. Based on consideration of the MNR, it is suggested that the enhancement of proton conductivity at low temperature can be well achieved by tuning lattice vibration frequency toward a desired isokinetic temperature.

Description of AC conductivity via Meyer-Neldel rule: A comparative study between oxide and chalcogenide systems

Nature of conductivity spectra in oxide and chalcogenide systems are found to be different, which should be indication of different conduction mechanisms via polaron hopping. This behaviour has been well explored using Meyer–Neldel rule (MNR), which provides microscopic information regarding conduction nature in different systems. Optical phonon assisted polaron hopping should impart this multiexcitation process of MNR. Microstructural information of present systems is also found to be helpful to validate conductivity data. A schematic model (nanocluster model) has been proposed to describe conduction mechanism in these complicated disordered solids. TEM micrographs and selected area electron diffraction (SAED) patterns reveal the agglomerates (cluster) in the oxide system, which may be favourable for stability of the system. More dislocations in the chalcogenide system should make the system unstable. This feature of instability should make them suitable candidates for more doping, which should increase their semiconducting nature.

Entropy Reduced Charge Transport and Energy Loss in Interfacial Zones of Polymer Nanocomposites

Polymer nanocomposites have higher energy storage density, much lower conductivity, and energy loss than the polymer matrices. The excellent performance may be originated from the deep-level localized states introduced by the interfacial zones between nanofillers and polymer matrices. However, the essential relation between the deep-level localized states and the composition, architecture, and configuration of polymer chains is still not clear. We investigate the temperature dependences of electrical conductivities of three types of energy storage polymer nanocomposites and find that they all obey the Meyer-Neldel (MN) compensation rule and the prefactor has an exponential relationship with the MN energy. It is found that the kinetic energy of electrons in the extended states of nanocomposites is the MN energy, which is related to the excitation of electrons by optical phonons. We propose to redefine the energy of localized states by the energy of optical phonons and the entropy of molecular conformations. It is found that the shape parameter of localized state distribution is related to the optical phonons and controlled by the composition, structure, and configuration of polymer chains, while the density of localized states is determined by the conformation and aggregate structure. We propose an optical phonon and entropy activated charge transport model, and the obtained conductivity equation is consistent with the experimental results. The entropy of molecular conformations can be used as a key factor to tailor the conductivity and energy loss of polymer nanocomposites. It provides a new perspective to study how to improve the energy storage performance of polymer nanocomposites.

Maintaining superior crystallinity and conductivity in boron-doped nc-Si ultra-thin films by hydrogen plasma treatment

In view of using doped nanocrystalline Si (nc-Si) as the emitter layer in nc-Si/crystalline-Si heterojunction solar cells, a very thin (≤ 50 nm) emitter layer with high conductivity and superior crystallinity is optimum. In the present work, p-nc-Si:H thin film prepared in inductively coupled plasma chemical vapor deposition, without using additional H2-dilution in [SiH4 + B2H6 (1% in H2)]-plasma, retains conductivity ~10−1 S cm−1 and crystallinity ~68% at a low thickness (t) ~50 nm. The charge carrier transport through the heavily doped nc-Si network demonstrates reverse Meyer–Neldel characteristics for t ≥ 50 nm. However, with reduction to t < 50 nm, the evolution of the ultra-nanocrystalline dominated amorphous network, accompanied by accumulation of Si–H–Si platelet-like components in the grain boundary, leads to a drastic reduction in conductivity to 10−4 S cm−1. In this context, the post-deposition and short-time hydrogen plasma treatment (PSHPT) on the as-deposited ultra-thin (t ~30 nm) film becomes instrumental in substantially enhancing the crystallinity from 40% to 69% and increasing conductivity by two orders of magnitude to 10−2 S cm−1. The network modification by PSHPT proceeds via transformation of the surface and sub-surface weak bonds and is significant for the ultra-thin film compared to the thick film, due to retaining a superior surface-to-bulk ratio.