Intrinsic Mobility Research Articles

Electron transport and the effect of current annealing in a two-point contacted hBN/graphene/hBN heterostructure device

In this work, we fabricated a 2D van der Waals heterostructure device in an inert nitrogen atmosphere by means of a dry transfer technique in order to obtain a clean and largely impurity free stack of hexagonal boron nitride (hBN)-encapsulated few-layer graphene. The heterostructure was contacted from the top with gold leads on two sides, and the device’s properties including intrinsic charge carrier density, mobility, and contact resistance were studied as a function of temperature from 4 K to 270 K. We show that the contact resistance of the device mainly originates from the metal/graphene interface, which contributes a significant part to the total resistance. We demonstrate that current annealing affects the graphene/metal interface significantly, whereas the intrinsic carrier density and carrier mobility of the hBN-encapsulated few-layer graphene are almost unaffected, contrary to often reported mobility improvements. However, after current annealing, a 75% reduction in the contact resistance improves the overall performance of such a heterostructure device and the backgate-dependent transfer curve becomes more symmetric with respect to the Dirac point. A maximum carrier mobility of 11200cm2V−1s−1 for this hBN/graphene/hBN heterostructure was measured at 4 K, showing good device performance, in particular, after current annealing.

Hole transport nature exploration of 4,4-Difluoro-8-(C4H3X)-4-bora-3a,4a-diaza-s-indacene (X = O, S, Se) (BODIPY) systems

ABSTRACT Charge transport and electronic character of fluorophore chalcogenides 4,4-Difluoro-8-(-XC4H3)-4-bora-3a,4a-diaza-s-indacene (X = O, S, Se) (BODIPY) derivatives were examined at the molecular level. The effect of chalcogenides was investigated on the transfer integrals, electron affinity (EA), frontier molecular orbitals (FMO), ionisation energy (IE), intrinsic mobility along with reorganisation energies. The ring dissimilarities within 4,4-difluoro-8-(-XC4H3)-4-bora-3a,4a-diaza-s-indacene (X = O, 2-/3-furyl (Comp1/Comp4)); (X = S, 2-/3-thienyl (Comp2/Comp4)) and (X = Se, 2-/3-selenenyl (Comp3/Comp6)) were compared systematically. Among BODIPY chalcogenides derivatives, 2-furyl substitution is more beneficial compared with 2-thienyl, 2-selenenyl and 3-furyl as the prior moiety significantly increases intrinsic hole mobility. The –S or –Se substitution at 2- or 3- position in place of –O at equivalent position reduces the structural polarisation from neutral to cation resulting in reduced hole reorganisation energies. The doping of –S or –Se at 2-position decreases the hole transfer integral in comparison to 2-furyl-substituted derivative. The effect of chalcogen atoms on 2- or 3- position is not so significant on the HOMO/LUMO energy levels. It is expected that –O doping at 2-position in furyl is supporting p-type charge transport channel. These results demonstrated that the studied BODIPY derivatives would be efficient hole transfer materials to be used in organic semiconductor devices.

Misfit epitaxial strain manipulated transport properties in cubic In2O3 hetero-epilayers

In this Letter, we report on the evolution of electronic properties governed by epitaxial misfit strain in cubic In2O3 epilayers grown on sapphire. At elevated growth temperature, the competition between the film/substrate lattice mismatch and the thermal expansion mismatch alters the macroscopic biaxial strain from compressive to tensile. Simultaneously, the electron concentration is tuned from degeneration to non-degeneration density below the Mott criterion. The observed surface electron accumulation and metal-insulator transition result from the oxygen deficiency formed at low growth temperature, while high-temperature epitaxy is favorable to achieve remarkably enhanced mobility. The effective strain-property coupling suggests that the improved oxygen stoichiometry and the Fermi level movement controlled by the biaxial strains are responsible for the Mott transition. The strain-mediated reduction of the electron effective mass contributes to the enhanced intrinsic mobility in tensile-strained In2O3 epilayers. These results highlight that strain engineering is an effective stimulus to manipulate the transport properties of oxide semiconductors with improved performance and unexpected functionalities.

Exploration of electronic nature and intrinsic mobility of 10-(1,3-dithiol-2-ylidene)anthracene based organic semiconductor materials

Electronic and charge transport nature of 10-(1,3-Dithiol-2-ylidene)anthracene based organic semiconductor materials (OSMs) have been explored at the molecular level. Effect of phenyl and 3,4-ethylenedioxythiophene of conjugated π-bridge and electron anchoring groups (−CHO and dicyanovinylene) was explored on various properties. The dicyanovinylene group lead to diminish electron reorganization energies while 3,4-ethylenedioxythiophene moiety enhance the hole transfer integrals. The dicyanovinylene groups along with 3,4-ethylenedioxythiophene moiety is favouring to reduce the HOMO and LUMO energy levels as well as their energy gap. The 3,4-ethylenedioxythiophene as bridge in OSMs would be decent to design p-type semiconductors. It is anticipated that dicyanovinylene as anchoring group might be a good approach for designing n-type semiconductors. The p- or n-type charge transport ability of anthracene derivatives was probed here. The transfer integrals, frontier molecular orbitals (FMO), ionization energy (IE), electron affinity (EA), reorganization energy, and intrinsic mobility showed that anthracene based derivatives might be proficient competitors to be applied in semiconductor devices.

Electron mobility and mode analysis of scattering for β-Ga2O3 from first principles

The electrical transport properties of β-Ga2O3 are studied by first-principles calculations. The calculated intrinsic electron Hall mobilities agree well with experiments, with intrinsic Hall factor decreasing monotonically from 1.54 at 100 K to 1.14 at 800 K. The anisotropy of electron mobility is weak due to the almost isotropic electron effective mass, which also results in nearly isotropic Seebeck coefficient and electronic contribution to the thermal conductivity. The mode analysis of phonon scattering reveals that the optical phonon scattering is almost entirely determined by the long-range polar interactions, whereas the acoustic phonon scattering also plays an important role especially at low temperatures. The intrinsic electron mobility is significantly overestimated even above room temperature by only considering the polar optical phonon scattering, in contrast to previous predictions from fitting of phenomenological models.

TiO2 Mesocrystals Processed at Low Temperature as the Electron-Transport Material in Perovskite Solar Cells.

TiO2 is the most widely used material for preparing the electron-transporting layer (ETL) in perovskite solar cells (PSCs). However, it requires a high-temperature sintering process. Moreover, the intrinsic defects and low electron mobility of TiO2 ETLs cause instability and hysteresis effects in PSCs. In this study, a mesoporous film composed of anatase TiO2 mesocrystals was facilely fabricated by a low-temperature route and then used as an ETL in PSCs for the first time. A satisfactory efficiency of 20.26 % can be achieved through delicate control of the entire device fabrication procedure. The optimal device, with an area of 1 cm2 , achieves an efficiency of 17.07 %. In comparison to the common TiO2 ETLs, those composed of TiO2 mesocrystals show the enhanced electron extraction and suppression of charge accumulation at the perovskite/ETL interface, resulting in improved photovoltaic performance and reduced hysteresis.

Channel mobility and contact resistance in scaled ZnO thin-film transistors

ZnO thin-film transistors (TFTs) with scaled channel lengths of 10 μm, 5 μm, 4 μm, and 2 μm exhibit increasing intrinsic channel electron mobility at a gate bias of 10 V (15 V) from 0.782 cm2/Vs (0.83 cm2/Vs) in the 10 μm channel length TFT to 8.9 cm2/Vs (19.04 cm2/Vs) for the channel length scaled down to 2 μm. Current-voltage measurements indicate an n-type channel enhancement mode transistor operation, with threshold voltages in the range of 8.4 V to 5.3 V, maximum drain currents of 41 μA/μm, 96 μA/μm, 193 μA/μm, and 214 μA/μm at a gate bias of 10 V, and breakdown voltages of 80 V, 70 V, 62 V, and 59 V with respect to channel lengths of 10 μm, 5 μm, 4 μm, and 2 μm. The channel electron mobility (excluding contact resistance) is extracted by the transmission line method (TLM) from the effective electron mobility (including contact resistance). The contact sheet resistance of4.6×105Ω/sq extracted from the measurements, which is 3.5× larger than the contact sheet resistance of 1.3×105Ω/sq obtained from the DFT calculation and the 1D self-consistent Poisson-Shrödinger simulation, largely limits the drive current in the scaled ZnO TFTs.

Meditación, historia, contención

Este ensayo presenta una visión de conjunto del modo en el cual el «giro» (Kehre) hacia el pensamiento ontohistórico, a medidados de los años ’30, impacta sobre la concepción aleteiológica que, siguiendo a E. Lask y E. Husserl, Heidegger elabora desde comienzos de los años ‘20 hasta Sein und Zeit. Sobre esa base, se ofrece también un intento de caracterización de la reformulación eventualista-kairológica de la aleteiología presentada en Beiträge zur Philosophie. La caracterización propuesta se lleva a cabo con arreglo a la distinción entre un nivel metahistórico de consideración, que corresponde al intento de pensar el seren su verdad en términos de la noción de «acontecimiento» (Ereignis), y un nivel propiamente histórico de consideración, que corresponde a la «hermenéutica de los dos comienzos». El pensar que medita históricamente el ser en su verdad sólo puede ser fiel a la intrínseca movilidad del ser mismo, si se ejerce en y desde la quietud de la contención, como temple animímico fundamental.

Lateral Epitaxial Heterostructures of Halide Perovskites for Diode Application

Solution-processed lateral epitaxial growth of two-dimensional (2D) halide perovskite heterostructures, multiheterostructures, and superlattices is a daunting task because of their soft fragile ionic bonding and high intrinsic ion mobility of halide ions. Recently, these structures have been successfully developed for Pb2+- and Sn2+-based 2D halide perovskites using various large organic molecules, and its potential energy application has been shown in thin-film electrical diodes.

Surface driven nano-morphology of poly 3-hexylthiophene film, and their photophysical, spectral and electronic traits

The present paper compiles, the substrate driven nano-morphology of fluorescent semiconducting poly 3-hexylthiophene (P3HT) polymer films and their effects on photophysical, spectral, and electronic behaviour. Surface morphological study reveals regular long sized aggregation and large crystalline structure of polymer thin film in liquid surface grown (LSG) film as compared to hard surface grown (HSG) film. Experimentally observed and computationally simulated Raman spectra show that HJ coupling dominates in LSG film compared to HSG film. LSG film yields the structured electronic absorption and emission spectra with increased radiative decay time, in comparison to HSG film. These indicate a decrease of non-radiative transitions in LSG film and support more crystalline nature of the P3HT film as well as improve intrinsic mobility and device parameters in the sandwiched structure of Schottky diode configuration. The findings show that LSG based electronic/photonic devices have a high potential for enhanced performance at a little cost.

A comparative study on intrinsic mobility of incoherent and semicoherent interfaces during the austenite to ferrite transformation

A straightforward approach to experimentally determine intrinsic interface mobility as well as extrinsic energy dissipation is proposed based on the measurements of total energy dissipation and interface velocity. These parameters have been comparatively studied for incoherent allotriomorphic ferrite (AF) and semicoherent Widmanstätten ferrite (WF) in an Fe-C alloy. It reveals that extrinsic energy dissipation for AF is negligibly small whereas that for WF is about 20J/mol, which should correspond to the dissipation by associated transformation strain. Furthermore, the intrinsic mobility of the semicoherent WF/austenite interface is found to be much smaller than the incoherent AF/austenite interface counterpart.

Survival time of Leptospira kirschneri serovar Grippotyphosa under different environmental conditions.

Leptospirosis is a re-emerging zoonotic disease of high medical importance that affects humans worldwide. Humans or animals acquire an infection with pathogenic leptospires either by direct contact with infected animals or by indirect contact to contaminated environment. Survival of Leptospira spp. in the environment after having been shed via animal urine is thus a key factor to estimate the risk of infection, but not much is known about the tenacity of pathogenic leptospires. Here, the survival time of both a laboratory strain and a field strain of L. kirschneri serovar Grippotyphosa in animal urine and their tenacity while drying was investigated and compared at different temperatures (15°C-37°C). Leptospira spp. are also often found in rivers and ponds. As the infection risk for humans and animals also depends on the spreading and survival of Leptospira spp. in these environments, the survival of L. kirschneri serovar Grippotyphosa was investigated using a 50-meter-long hose system simulating a water stream. Both strains did not survive in undiluted cattle or dog urine. Comparing different temperatures and dilution media, the laboratory strain survived the longest in diluted cattle urine with a slightly alkaline pH value (3 days), whilst the field strain survived in diluted dog urine with a slightly acid pH value up to a maximum of 24 h. Both strains did not survive drying on a solid surface. In a water stream, leptospires were able to move faster or slower than the average velocity of the water due to their intrinsic mobility but were not able to survive the mechanical damage caused by running water in the hose system. From our results we conclude, that once excreted via animal urine, the leptospires immediately need moisture or a water body to survive and stay infectious.

Accuracy of Y-function methods for parameters extraction of two-dimensional FETs across different technologies

The accuracy of contact resistance values of two-dimensional field-effect transistors extracted with the \textit{Y}-function considering the impact of the intrinsic mobility degradation is evaluated here. The difference between methodologies that take this factor into account and ignore it is pointed out by a detailed analysis of the approximations of the transport model used for each extraction. In contrast to the oftenly used approach where the intrinsic mobility degradation is neglected, a \textit{Y}-function-based method considering a more complete transport model yields contact resistance values similar to reference values obtained by other intricate approaches. The latter values are more suitable also to describe experimental data of two dimensional devices of different technologies. The intrinsic mobility degradation factor of two-dimensional transistors is experimentally characterized for the first time and its impact on the device performance is described and evaluated.

Crystallized Monolayer Semiconductor for Ohmic Contact Resistance, High Intrinsic Gain, and High Current Density.

The contact resistance limits the downscaling and operating range of organic field-effect transistors (OFETs). Access resistance through multilayers of molecules and the nonideal metal/semiconductor interface are two major bottlenecks preventing the lowering of the contact resistance. In this work, monolayer (1L) organic crystals and nondestructive electrodes are utilized to overcome the abovementioned challenges. High intrinsic mobility of 12.5 cm2 V-1 s-1 and Ohmic contact resistance of 40 Ω cm are achieved. Unlike the thermionic emission in common Schottky contacts, the carriers are predominantly injected by field emission. The 1L-OFETs can operate linearly from VDS =-1V to VDS as small as -0.1mV. Thanks to the good pinch-off behavior brought by the monolayer semiconductor, the 1L-OFETs show high intrinsic gain at the saturation regime. At a high bias load, a maximum current density of 4.2 µA µm-1 is achieved by the only molecular layer as the active channel, with a current saturation effect being observed. In addition to the low contact resistance and high-resolution lithography, it is suggested that the thermal management of high-mobility OFETs will be the next major challenge in achieving high-speed densely integrated flexible electronics.

Characteristic boundaries associated with three-dimensional twins in hexagonal metals.

Twinning is a critically important deformation mode in hexagonal close-packed metals. Twins are three-dimensional (3D) domains, whose growth is mediated by the motion of facets bounding the 3D twin domains and influences work hardening in metals. An understanding of twin transformations therefore necessitates that the atomic-scale structure and intrinsic mobilities of facets be known and characterized. The present work addresses the former point by systematically characterizing the boundary structures of 3D twins in magnesium using high-resolution transmission electron microscopy (HRTEM). Eight characteristic facets associated with twin boundaries are reported, five of which have never been experimentally observed before. Further, molecular dynamics simulations suggest that the formation and motion of these facets is associated with the accumulation of twinning dislocations. This work provides insights into understanding the structural character of 3D twins and serves to develop strategies for modulating twin kinetics by modifying twin boundaries, such as solute segregation.

Enhancing the Resilience of Low Earth Orbit Remote Sensing Satellite Networks

The Low Earth orbit Remote Sensing (LRS) satellite network is envisioned as an essential component of bolstering space information applications, thus extending conventional ground information applications to the on-board space information applications. However, it inevitably faces grave challenges imposed by the dynamics of the satellite network's topology, by the intermittence of Inter-Satellite communication Links (ISLs) as well as by the mobility-induced satellite-access switching of mobile terminals. Hence, this is a very different networking landscape from that of the terrestrial Internet. Against these challenging problems, we propose a resilient networking architecture for LRS Satellite Networks (LRS-SNs), with special emphasis on their dynamic routing, resilient transmission and their intrinsic mobility. Specifically, path-quality aided and lifetime-aware dynamic routing is proposed for enhancing the routing against dynamic topology changes. Hop-by-hop data transmission is relied upon for providing transmission resilience against ISL intermittence. Furthermore, data caching is invoked for providing resilience against intermittent communications imposed by dynamic satellite access switching. We employ a semi-physical simulation platform for evaluating the achievable performance of the proposed resilient network architecture.

High-Performance and Reliable Lead-Free Layered-Perovskite Transistors.

Perovskites have been intensively investigated for their use in solar cells and light-emitting diodes. However, research on their applications in thin-film transistors (TFTs) has drawn less attention despite their high intrinsic charge carrier mobility. In this study, the universal approaches for high-performance and reliable p-channel lead-free phenethylammonium tin iodide TFTs are reported. These include self-passivation for grain boundary by excess phenethylammonium iodide, grain crystallization control by adduct, and iodide vacancy passivation through oxygen treatment. It is found that the grain boundary passivation can increase TFT reproducibility and reliability, and the grain size enlargement can hike the TFT performance, thus, enabling the first perovskite-based complementary inverter demonstration with n-channel indium gallium zinc oxide TFTs. The inverter exhibits a high gain over 30 with an excellent noise margin. This work aims to provide widely applicable and repeatable methods to make the gate more open for intensive efforts toward high-performance printed perovskite TFTs.

Impact of Chirality on Hydrogen-Bonded Supramolecular Assemblies and Photoconductivity of Diketopyrrolopyrrole Derivatives.

Hydrogen bonds can efficiently guide the self-assembly of organic materials, enabling to tune the properties of the aggregation processes. In the case of π-conjugated materials, several parameters such as temperature, concentration and solvent can be used to modify the aggregation state while tuning the optoelectronic properties. Chirality can be included within the impacting parameters due to the differences in molecular packing. Here, chiral and achiral thiophene-capped diketopyrrolopyrrole derivatives were designed and synthesized containing amide bonds, with the aim to study the interplay between chiral assemblies and their stabilization through hydrogen-bonding. Differences in aggregation properties were observed with spectroscopy and microscopy, and a contactless microwave-based technique was used to study their intrinsic charge carrier mobility. The positive role of hydrogen-bonding has been highlighted and the differences between chiral and achiral compounds have been elucidated.

Experimental Investigation of naphthalene based organic thin-film transistors by combining a polymer dielectric and a carrier injection layer

In this work, thermally evaporated organic thin-film transistors (OTFTs) based on a naphthalene diimide derivative (NTCDI-C13) were fabricated and the contact doping process with cesium fluoride (CsF) was investigated. The OTFTs incorporated a polymer dielectric layer (CYTOPTM), which contributed to the suppression of 3D needle-like NTCDI-C13 crystallite formation during the evaporation process. The results demonstrated that the combination of CsF and CYTOP markedly improved the devices, resulting in an intrinsic mobility of 0.3 cm2/Vs and a threshold voltage of 10 V. The stability of the devices was also investigated under ambient atmospheric conditions. The TFTs exhibited minimal performance loss, and it was observed that there was potential overestimation of the mobilities after a few minutes in ambient air.

Towards theoretical framework for probing the accuracy limit of electronic transport properties of SnSe2 using many-body calculations

A theoretical framework to investigate the accuracy limit of phonon-limited carrier mobility in intrinsic n-type SnSe2 has been developed by solving the Boltzmann transport equation based on ab initio calculated electron-phonon interactions. The electron-phonon coupling matrix elements have been computed using maximally localized Wannier functions and density functional perturbation theory. The intrinsic electron mobility of ∼ 8.75 cm2V-1s-1 has been achieved at 300 K, incorporating spin-orbit coupling, many-body quasiparticle corrections, and iterative solution of the Boltzmann transport equation using dense sampling of the Brillouin zone. The calculated intrinsic mobility is in close agreement with the experimental values. Furthermore, the electron mean-free path, electrical conductivity, and Seebeck coefficient have been calculated for SnSe2 under varying temperatures. The maximum mean-free path of 20 nm has been achieved for electrons at 300 K. This contribution provides a comprehensive method to investigate the transport properties and presents a framework towards the accuracy limit of prototypical SnSe2.