Temperature Dependence Of Mobility Research Articles

Photoexcited charge-carrier transport in monolayer and bulk bismuth oxyiodide: the impact of the polaronic effect and deep-level defects

Bismuth oxyiodide (BiOI), in monolayer and bulk forms, is a lead-free semiconductor material that has sparked increased interest for applications in perovskite solar cells and x-ray detectors. It is vital to clarify the transport nature of photoexcited charge-carriers to improve device performance. However, the transport scattering mechanisms remain poorly understood, and a detailed explanation of the measured charge-carrier mobilities in this material system is still under scrutiny. Herein, we implement transport scattering models that include LO phonon scattering based on the polaronic effect and ionized impurity scattering due to deep-level defects to elucidate photoexcited charge mobilities. We found that large polarons produced by photoexcited charge carriers coupled with LO phonon modes of 86 cm−1 and 156 cm−1 play a key role in the transport process of the BiOI system. Large polaron mobility provides a good explanation for the measured mobilities in single crystal samples between 26–83 cm2V−1s−1 at 295 K. The estimated results from both transport scattering models agree with the temperature-dependent mobilities measured in thin-film samples, between 13 cm2V−1s−1 at 5 K and 3 cm2V−1s−1 at 295 K. This work provides important insights into a band-like transport feature in the BiOI system.

Low field mobility in bulk GaN and its ternary AlGaN/GaN compounds (quantum kinetic approach)

Analytical expressions for the low-field mobility of charge carrier gases with three-(3D), two-(2D) and one-(1D) dimensionalities are obtained. Multi-ion ionized impurities scattering, acoustic and polar optic phonons are considered as scattering mechanisms. The calculated values of mobility are compared to known experimental data for bulk (3D) n-and p-type wurtzite, n-type zinc-blende GaN crystals and low dimensional (2D and 1D) ternary GaAlN compounds. The resulting analytical expressions give the dependences of mobility on dimensionality of charge carrier gas, its density, effective mass, temperature and confining dimensions. A comparison of the experimental and calculated temperature dependences of the mobility in bulk GaN crystals (3D) and in AlGaN/GaN nanowires (1D) shows that the mobility at 100\\,{\ ext{K}}$?> T>100K is determined by the scattering of charge carriers by polar optical phonons with an energy of 91.2 meV. The temperature dependences of mobility in Al0.25Ga0.75N/GaN heterostructures (2D) at 100\\,{\ ext{K}}$?> T>100K are in consistent with experiment for electron scattering by polar optical phonons with a noticeably higher energy of 160 meV. We associate this fact with the heterointerface, which according to well-known theoretical studies can change both the strength of electron polar optical phonons scattering and the energy of the phonons.

Temperature dependence of hole mobility in methylated germanane field-effect transistor

Methylated germanane, a layered material in which single-layer germanium is terminated by methyl groups, was utilized as a channel material of back-gate-type FETs. Titanium (Ti) and nickel (Ni) were used as source and drain electrodes of FETs, and the FET with the Ti electrode showed ambipolar characteristics, whereas that with the Ni electrode showed p-type characteristics. The maximum hole mobility at RT is 380 cm2V−1s−1, which is higher than those of typical transition metal dichalcogenides. The mobility changes with temperature T according to the T −3/2 law at temperatures ranging from 243 to 343 K, suggesting that the major scattering factor of holes is acoustic phonons.

Effect of temperature modulation on the performance of top contact bottom gate organic thin film transistor

This research article investigates the influence of temperature variations on the performance parameters of Top Contact Bottom Gate (TCBG) Organic Thin Film Transistors (OTFTs). Employing the Arrhenius equation and Schottky emission model, the study explores temperature-dependent charge carrier mobility and injection mechanisms. Analyzing a wide range of parameters, the research unveils a complex interplay between temperature and OTFT behavior. The linear and saturation mobilities exhibit a decline due to enhanced carrier-phonon interactions and lattice vibrations. Transconductance and ION/IOFF ratio display a concomitant decrease at higher temperatures, indicative of the heightened susceptibility of OTFT performance to temperature fluctuations. The depreciation in subthreshold slope and threshold voltage with rising temperatures underscores the influence of temperature on trap states. The research emphasizes the importance of considering temperature’s impact during OTFT design for diverse applications, enhancing the reliability and functionality of organic electronic devices.

A Sub-1-V Nanopower MOS-Only Voltage Reference

A novel low-power MOS-only voltage reference is presented. The Enz–Krummenacher–Vittoz (EKV) model is adopted to provide a new perspective on the operating principle. The normalized charge density, introduced as a new variable, serves as an indicator when trimming the output temperature coefficient. The proposed voltage reference consists of a specific current generator and a 5-bit trimmable load. Thanks to the good match between the current source stage and the output stage, the nonlinear temperature dependence of carrier mobility is automatically canceled out. The circuit is designed using 55 nm COMS technology. The operating temperature ranges from −40 °C to 120 °C. The average temperature coefficient of the output voltage can be reduced to 21.7 ppm/°C by trimming. The power consumption is only 23.2 nW with a supply voltage of 0.8 V. The line sensitivity and the power supply rejection ratio at 100 Hz are 0.011 %/V and −89 dB, respectively.

On Analytical Modeling of Hopping Transport of Charge Carriers and Excitations in Materials with Correlated Disorder.

Spatial-energy correlations strongly influence charge and exciton transport in weakly ordered media such as organic semiconductors and nanoparticle assemblies. Focusing on cases with shorter-range interparticle interactions, we develop a unified analytic approach that allows us to calculate the temperature and field dependence of charge carrier mobility in organic quadrupole glasses and the temperature dependence of the diffusion coefficient of excitons in quantum dot solids. We obtain analytic expressions for the energy distribution of hopping centers, the characteristic escape time of charge/exciton from the energy well stemming from energy correlations around deep states, and the size of the well. The derived formulas are tested with Monte Carlo simulation results, showing good agreement and providing simple analytic expressions for analysis of charge and exciton mobility in a broad range of partially ordered media.

Lunar polar volatile remobilization in regolith-filled craters

Under lunar polar cold traps, volatile molecules within porous regolith may experience temperature and depth dependent slow mobility. Many degraded lunar craters exhibit thick regolith fill based on models of topographic diffusion and observations of fresh and degraded craters. Regolith has a low thermal conductivity relative to megaregolith and may act as a blanket for internal lunar heat flow, leading to increased temperatures at depth. We develop 2D thermal models of fresh and regolith-filled lunar craters over depths of meters to hundreds of meters below the surface. We find that the base of the stability and slow mobility zones migrate upward with regolith fill, which leads to temperatures that may increase the sublimation rate of volatiles at depth. For a notional cold trap crater 1.6 km in diameter and 3.6 billion years old, topographic diffusion fills it with approximately 90 m of regolith, and the regolith fill's blanketing effect causes the 110 K isotherm to shift about 180 m upward. This places it approximately 25 m below the current cold trap surface and well above the initial crater floor. The slow water ice mobility zone below the 110 K isotherms also shifts upward with regolith fill, potentially increasing volatile concentrations at shallower depths. These secondary volatile concentrations may be targets for sampling and testing hypotheses of volatile system processes. In addition, remobilized volatile concentrations may be a resource for future In-Situ Resource Utilization (ISRU) applications. The thick regolith fill in degraded craters and volatile remobilization potential in lunar subsurface cold traps have implications for future exploration instruments, sampling, and ISRU architectures.

Temperature-dependent hole mobility in pyrene-thiophene-based room-temperature discotic liquid crystals.

π-Conjugated pyrene-thiophene-based room-temperature discotic liquid crystals armed with four peripheral aliphatic chains are reported to study their potential use in a hole-transporting organic semiconductor. The charge carrier mobility studies using the ToF method revealed room temperature hole mobility in the order of 10-4 cm2 V-1 s-1 for both mesogens. However, the mobility values for compound 1a were observed in the order of 10-3 cm2 V-1 s-1 at high temperatures. Such molecular systems can potentially be used in nonlinear organic electronic applications.

The critical role of temperature-dependent mobilities in determining the open-circuit voltage of bulk-heterojunction organic solar cells

While solution-processed bulk-heterojunction organic solar cells (OSCs) continue to attract attention as their efficiencies approach 20%, the physical origin of the non-radiative energy loss in OSCs remains under debate. Understanding the temperature dependence of open-circuit voltage (VOC) is thus important because it provides unique insights into the origin of energy loss. Herein, we simulate the VOC vs T relation of PTB7-Th:PC71BM bulk-heterojunction OSCs within the range of 160–295 K by incorporating experimentally measured temperature-dependent mobilities into the drift-diffusion model, assuming bimolecular recombination as the primary recombination mechanism. Significantly, we find that the temperature dependence of VOC can only be correctly reproduced by the model when the temperature dependence of the carrier mobilities is taken into account. The effect of the Langevin reduction coefficient on the temperature dependence of VOC is also investigated.

Electrical properties of silicon-implanted β-Ga2O3:Fe crystals

Ion implantation is a promising method for the development of β-Ga2O3-based technologies and devices. However, the physical principles of ion implantation for this particular semiconductor are still at the early stage of development. One of the primary tasks is the study of electrical properties of the ion-doped layers. In this work, we have investigated the electrical parameters of layers produced by ion implantation of a shallow donor impurity—silicon—into a semi-insulating β-Ga2O3 doped with iron and having a surface orientation of (−201). It is established that the activation efficiency of the implanted impurity significantly exceeds unity after post-implantation annealing at high temperatures. This indicates that not only silicon itself contributes to conductivity, but also defects formed with its (and, probably, iron) participation are involved. The temperature dependence of electron mobility is consistent with the theoretically calculated one under the assumption that, apart from shallow donors, there are also deep defect-associated donors and acceptors. It is assumed that the established properties are specific for the case of direct Si implantation into β-Ga2O3 doped with Fe.

Different temperature dependence of mobility in n- and p-channel 4H-SiC MOSFETs

The impact of interface state density (D it) near the conduction band edge (E C) and the VB edge (E V) on the field-effect mobility (μ FE) of NO- and N2-annealed n- and p-channel MOSFETs was investigated. With lowering the temperature, μ FE of n-channel MOSFETs decreased whereas μ FE increased in p-channel devices. Despite the comparable D it values near E C and E V, p-channel MOSFETs have less trapped carriers due to a deeper surface Fermi level caused by the larger effective masses of holes, resulting in smaller Coulomb scattering, and this may cause the different temperature dependence of μ FE in n- and p-channel MOSFETs.

Bayesian optimization approach to quantify the effect of input parameter uncertainty on predictions of numerical physics simulations

An understanding of how input parameter uncertainty in the numerical simulation of physical models leads to simulation output uncertainty is a challenging task. Common methods for quantifying output uncertainty, such as performing a grid or random search over the model input space, are computationally intractable for a large number of input parameters represented by a high-dimensional input space. It is, therefore, generally unclear as to whether a numerical simulation can reproduce a particular outcome (e.g., a set of experimental results) with a plausible set of model input parameters. Here, we present a method for efficiently searching the input space using Bayesian optimization to minimize the difference between the simulation output and a set of experimental results. Our method allows explicit evaluation of the probability that the simulation can reproduce the measured experimental results in the region of input space defined by the uncertainty in each input parameter. We apply this method to the simulation of charge-carrier dynamics in the perovskite semiconductor methyl-ammonium lead iodide (MAPbI3), which has attracted attention as a light harvesting material in solar cells. From our analysis, we conclude that the formation of large polarons, quasiparticles created by the coupling of excess electrons or holes with ionic vibrations, cannot explain the experimentally observed temperature dependence of electron mobility.

Effect of oxygen and nitrogen sensitization on structural, optical and electrical properties of PbSe thin films

An effective two-step sensitization technique was implemented in PbSe thin films, leading to a remarkable improvement in the optoelectronic performance of PbSe photodetectors. The phase composition, surface and cross-sectional morphology, temperature-dependent carrier concentration and mobility as well as the detectability of PbSe films after sensitization were systematically investigated using characteristic techniques. The optimal PbSe film oxygen sensitized at 450 °C exhibited a room-temperature photodetection with a carrier concentration of 5.31 × 1016 cm−3, carrier mobility of 16.52 cm2/V−1s−1, and detectivity of 2.25 × 109 Jones. High-temperature argon heat treatment and oxygen sensitization of PbSe films are expected to suppress recombination losses and significantly improve the optoelectronic properties of sensitized PbSe films due to enhanced carrier separation and transport. The enhanced photoresponse mechanism of the PbSe films through two-step sensitization method was also discussed. These results suggest that the proposed method can be applied to high-performance lead selenide photodetectors.

HfSe2: Unraveling the microscopic reason for experimental low mobility.

Monolayer HfSe2, in the family of transition metal dichalcogenides (TMDCs), is a potential thermoelectric candidate due to its low thermal conductivity. While its mobility remains low as in other 2D TMDCs is inconceivable for electronic and thermoelectric applications. Earlier theoretical attempts have failed to give justification for the orders of low experimental mobility obtained for monolayer HfSe2. We calculate the carrier mobility in the framework of the density functional perturbation theory in conjunction with the Boltzmann transport equation and correctly ascertain the experimental value. We also calculate the carrier mobility with the previously employed method, the deformation potential (DP) model, to figure out the reason for its failure. We found that it is the strong electron-optical phonon interaction that is causing the low mobility. As the DP model does not account for the optical phonons, it overestimates the relaxation time by an order of two and also underestimates the temperature dependence of mobility. A strong polar type interaction is evidenced as a manifestation of a discontinuity in the first derivative of the optical-phonons at the K and Γ points as well as a dispersive optical phonon at the K point. We also included the spin-orbit coupling which leads to an energy splitting of ∼330meV and significantly affects mobility and scattering rates.

Transiently delocalized states enhance hole mobility in organic molecular semiconductors.

Evidence shows that charge carriers in organic semiconductors self-localize because of dynamic disorder. Nevertheless, some organic semiconductors feature reduced mobility at increasing temperature, a hallmark for delocalized band transport. Here we present the temperature-dependent mobility in two record-mobility organic semiconductors: dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]-thiophene (DNTT) and its alkylated derivative, C8-DNTT-C8. By combining terahertz photoconductivity measurements with atomistic non-adiabatic molecular dynamics simulations, we show that while both crystals display a power-law decrease of the mobility (μ) with temperature (T) following μ ∝ T -n, the exponent n differs substantially. Modelling reveals that the differences between the two chemically similar semiconductors can be traced to the delocalization of the different states that are thermally accessible by charge carriers, which in turn depends on their specific electronic band structure. The emerging picture is that of holes surfing on a dynamic manifold of vibrationally dressed extended states with a temperature-dependent mobility that provides a sensitive fingerprint for the underlying density of states.

The electronic properties of boron-doped germanium nanocrystals films

Various doping concentrations of boron (B)-doped germanium nanocrystal (Ge NC) films were prepared using the plasma-enhanced chemical vapor deposition (PECVD) technique followed by thermal annealing treatment. The electronic properties of B-doped Ge NCs films combined with the microstructural characterization were investigated. It is worthwhile mentioning that the Hall mobilities {mu }_{mathrm{Hall}} of Ge NCs films were enhanced after B doping and reached to the maximum of 200 cm2 V−1, which could be ascribed to the reduction in surface defects states in the B-doped films. It is also important to highlight that the temperature-dependent mobilities {mu }_{mathrm{H}}(T) exhibited different temperature dependence trends in the Ge NCs films before and after B doping. A comprehensive investigation was conducted to examine the distinct carrier transport properties in B-doped Ge NC films, and a detailed discussion was presented, focusing on the scattering mechanisms involved in the transport process.

One-Step Passivation of Both Sulfur Vacancies and SiO2 Interface Traps of MoS2 Device.

Transition metal dichalcogenides (TMDs) benefit electrical devices with spin-orbit coupling and valley- and topology-related properties. However, TMD-based devices suffer from traps arising from defect sites inside the channel and the gate oxide interface. Deactivating them requires independent treatments, because the origins are dissimilar. This study introduces a single treatment to passivate defects in a multilayer MoS2 FET. By applying back-gate bias, protons from an H-TFSI droplet are injected into the MoS2, penetrating deeply enough to reach the SiO2 gate oxide. The characterizations employing low-temperature transport and deep-level transient spectroscopy (DLTS) studies reveal that the trap density of S vacancies in MoS2 drops to the lowest detection level. The temperature-dependent mobility plot on the SiO2 substrate resembles that of the h-BN substrate, implying that dangling bonds in SiO2 are passivated. The carrier mobility on the SiO2 substrate is enhanced by approximately 2200% after the injection.

Electronic-, Optical-, and Temperature-Dependent Carrier Mobility Simulations of Perovskite-Type Liganded PbS Quantum Dot Array

Recent experimental results suggest that higher mobility of perovskite-type ligand passivated PbS quantum dots (QDs) could be useful for efficient solar cell applications. However, theoretical understanding of the mechanism through first principal modeling is still lacking. In this study, electronic-, optical-, and temperature-dependent carrier mobility for perovskite ligand passivated PbS QD array is calculated by using the first-principles density functional theory (DFT) combined with the nonequilibrium Green’s function (NEGF) technique and a molecular dynamics (MD)-Landauer approach. It is found that formamidinium (FA)-liganded QDs have higher mobility and enhanced optical absorption comparing to that of Cl-liganded QDs. The difference could be understood through the intermediate band featured electronic structure.

Temperature Dependency of Ion Mobility in Synthetic Ester by Dielectric Response Analysis in Time and Frequency Domain

Synthetic ester is a promising alternative to mineral oil for emerging applications relying on high-power static conversion, such as solid-state transformers (SST). The highly compact components used in SSTs must fulfill MV-DC insulation requirements to guarantee the safe operation of the system, therefore, their design relies on the characterization of the dielectric stress caused by the electric field. The prediction of the electric field induced by DC voltages requires analyzing the conduction phenomena in the liquid, including the effect of charge transport due to ion drift. In this scenario, one of the critical parameters that determine the transport of charge and the resulting electric field distribution is the mobility of ions μ; the value of μ in synthetic ester is available only at room temperature, however, investigations on other dielectric liquids indicate a significant temperature dependency, which therefore needs to be characterized. In this paper, the temperature dependency of μ in synthetic ester liquid is determined by comparing alternative methodologies based on the analysis of the dielectric response in the time and frequency domain, and the viscosity of the fluid. The characteristics obtained by these methodologies are consistent; the temperature dependency of μ obeys the Arrhenius law and an increase of one order of magnitude starting from 1.1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">–10</sup> m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /Vs is observed in the 303K–353K temperature range.

Thermal Management Enables Stable Perovskite Nanocrystal Light-Emitting Diodes with Novel Hole Transport Material.

The severely insufficient operational lifetime of perovskite light-emitting diodes (LEDs) is incompatible with the rapidly increasing external quantum efficiency, even as it approaches the theoretical limit, thereby significantly impeding the commercialization of perovskite LEDs. In addition, Joule heating induces ion migration and surface defects, degrades the photoluminescence quantum yield and other optoelectronic properties of perovskite films, and induces the crystallization of charge transport layers with low glass transition temperatures, resulting in LED degradation under continuous operation. Here, a novel thermally crosslinked hole transport material, poly(FCA60 -co-BFCA20 -co-VFCA20 ) (poly-FBV), with temperature-dependent hole mobility is designed, which is advantageous for balancing the charge injection of the LEDs and limiting the generation of Joule heating. The optimised CsPbI3 perovskite nanocrystal LEDs with poly-FBV realise approximately a 2-fold external quantum efficiency increase over the LED with commercial hole transport layer poly(4-butyl-phenyl-diphenyl-amine) (poly-TPD), owing to the balanced carrier injection and suppressed exciton quenching. Moreover, because of the Joule heating control provided by the novel crosslinked hole transport material, the LED utilising crosslinked poly-FBV has a 150-fold longer operating lifetime (490min) than that utilizing poly-TPD (3.3min). The study opens a new avenue for the use of PNC LEDsin commercial semiconductor optoelectronic devices.