High Electron Carrier Mobilities Research Articles

Single-layer ZnGaInS4: Desirable bandgap and high carrier separation efficiency for optoelectronics

Two-dimensional optoelectronic materials with desirable bandgaps and high carrier separation efficiency are in urgent need. Herein, single-layer ZnGaInS4 is designed and thoroughly studied by first-principles calculations. Our calculations reveal the excellent stability of single-layer ZnGaInS4, and the small cleavage energy demonstrates the feasibility to exfoliate single-layer ZnGaInS4 from bulk counterparts. At the HSE06 level, single-layer ZnGaInS4 has a moderate bandgap of 2.05 eV, and its valence band maximum and conduction band minimum are spatially separated, thus impeding the electron-hole pair formation and enhancing the photoelectronic performance. In the visible region, single-layer ZnGaInS4 exhibits an optical absorption coefficient of ∼ 105 cm−1. Notably, single-layer ZnGaInS4 possesses high electron carrier mobility and low hole carrier mobility, further affirming the effective carrier separation. Another attractive characteristic is that single-layer ZnGaInS4 has anisotropic hole mobility. The desirable bandgap and high separation efficiency of generated carriers, together with abundant optical absorption, promise single-layer ZnGaInS4 is a hopeful candidate in atomic-thick optoelectronic devices.

Prediction of new 2D Hf2Br2N2 monolayer as a promising candidate for photovoltaic applications

In the present work, the structural and optoelectronic properties of pristine and strained hexagonal Hf2Br2N2 monolayer have been investigated using the first-principles calculations. The binding energy, phonon dispersion calculations, and molecular dynamics simulations demonstrated that this monolayer has dynamic and thermal stabilities depending. It was revealed that the unstrained Hf2Br2N2 monolayer is semiconducting with an indirect bandgap of 1.809 eV/2.853 eV using PBE/HSE06 methods, which is perfect for powerful light absorption. Besides, the results show that the biaxial strain is an effective tool for adjusting the energy gap where the indirect energy gap under the strain effects ranged within a range of 2.791 eV at −6% to 2.968 eV at 6%. Our results show that the Hf2Br2N2 monolayer has a high electron carrier mobility of 7780.2 cm2/V.s. Furthermore, it was found that the Hf2Br2N2 monolayer has the strongest absorption ranging from IR to UV region of the light spectrum. The outcomes of this work revealed that biaxial strain can be an effective technique for tuning the optoelectronic properties of the Hf2Br2N2 monolayer. Moreover, these results confirm that this monolayer can be suitable for photodetectors and photovoltaics applications.

Novel two-dimensional beta-XTe (X = Ge, Sn, Pb) as promising room-temperature thermoelectrics.

In this paper, we designed novel low-symmetry two-dimensional (2D) structures based on conventional XTe (X = Ge, Sn, Pb) thermoelectrics with large average atomic mass. The first-principles calculations combined with Boltzmann transport theory show that the beta-XTe exhibit good stability, high electron carrier mobility, and ultralow ΚL. The subsequent analyses show that the ultralow ΚL stems from the coexistence of resonant bonding, weak bonding, and lone-pair electrons in beta-XTe, which leads to large anharmonicities. On the other hand, the lowest energy conduction band of beta-GeTe and beta-SnTe show the convergence of the low-lying Ʃ band, which is the source of the high-power factor in the two systems. The calculated maximum ZT of beta-XTe (X = Ge, Sn, Pb) are 3.08, 1.60, and 0.57 at 300K, respectively, which is significantly greater than that of the previously reported high-symmetry 2D alpha-XTe and the commercial thermoelectrics. We hope that this work can provide important guidance for the development of thermoelectric materials.

B5N3 and B7N5 Monolayers with High Carrier Mobility and Excellent Optical Performance.

An ab initio evolutionary search algorithm was combined with density functional theory (DFT) calculations to predict a series of 2-D BxNy (1 < x/y ≤ 2). Particularly, B5N3 and B7N5 monolayers have sufficiently low formation enthalpy and excellent dynamic stability that make them promising for synthesis in experiments. Electronic structure calculations reveal that B5N3 and B7N5 monolayers possess an indirect band gap of 1.99 eV and a direct band gap of 2.40 eV, respectively. The calculated absorption coefficients for B5N3 and B7N5 monolayers are significantly improved in the low end of the visible region compared with that of 2-D h-BN. Moreover, our calculations reveal that both B5N3 and B7N5 monolayers have high electron carrier mobilities. The narrow band gaps, high carrier mobilities, strong near-ultraviolet absorption, and high synthesis possibility of B5N3 and B7N5 monolayers render them promising new materials for application in novel electronics and environmentally benign solar energy conversion.

Predicted septuple-atomic-layer Janus MSiGeN4 (M = Mo and W) monolayers with Rashba spin splitting and high electron carrier mobilities

In this work, Janus monolayers are predicted for a new 2D MA2Z4 family by means of first-principles calculations. The predicted MSiGeN4 (M = Mo and W) monolayers exhibit dynamic, thermodynamic and mechanical stability, and they are indirect band-gap semiconductors.

Large piezoelectric coefficients combined with high electron mobilities in Janus monolayer XTeI (X = Sb and Bi): A first-principles study

The absence of both the inversion symmetry and out-of-plane mirror symmetry together with spin–orbit coupling (SOC) can induce novel electronic and piezoelectric properties. In this work, the piezoelectric properties along with carrier mobilities of Janus monolayer XTeI (X=Sb and Bi) are studied by density functional theory. By using generalized gradient approximation (GGA) plus SOC, they are found to be indirect gap semiconductors with the Rashba spin splitting. The piezoelectric tensors of Janus monolayer XTeI (X=Sb and Bi) are reported by using the density functional perturbation theory. Due to lacking both the inversion symmetry and out-of-plane mirror symmetry for Janus monolayer XTeI (X=Sb and Bi), both in-plane and out-of-plane piezoelectric effects can be observed, and the large piezoelectric coefficients are predicted (e.g., d11=12.95pm/V for SbTeI and d11=8.20pm/V for BiTeI), which are comparable and even higher than the ones of many other two-dimensional materials and other well-known bulk piezoelectric materials, especially for out-of-plane piezoelectric coefficients. With GGA+SOC, the high electron carrier mobilities are obtained, and the electron mobility of BiTeI along armchair direction reaches up to about 1319cm2V−1s−1. The carrier mobility shows a rather pronounced anisotropy between electron and hole/armchair and zigzag directions. It is found that tensile strain can improve the piezoelectric coefficients d11 of Janus monolayer XTeI (X=Sb and Bi). For example, at 4% strain, the d11 of SbTeI (BiTeI) is up to 20.12 pm/V (11.48 pm/V), compared with unstrained 12.95 pm/V (8.20 pm/V). Our works imply Janus monolayer XTeI (X=Sb and Bi) have potential applications in flexible electronics and piezoelectric devices, and can stimulate further experimental works.

A New Three-Dimensional Subsulfide Ir2In8S with Dirac Semimetal Behavior

Dirac and Weyl semimetals host exotic quasiparticles with unconventional transport properties, such as high magnetoresistance and carrier mobility. Recent years have witnessed a huge number of newly predicted topological semimetals from existing databases; however, experimental verification often lags behind such predictions. Common reasons are synthetic difficulties or the stability of predicted phases. Here, we report the synthesis of the type-II Dirac semimetal Ir2In8S, an air-stable compound with a new structure type. This material has two Dirac crossings in its electronic structure along the Γ-Z direction of the Brillouin zone. We further show that Ir2In8S has a high electron carrier mobility of ∼10 000 cm2/(V s) at 1.8 K and a large, nonsaturating transverse magnetoresistance of ∼6000% at 3.34 K in a 14 T applied field. Shubnikov de-Haas oscillations reveal several small Fermi pockets and the possibility of a nontrivial Berry phase. With its facile crystal growth, novel structure type, and striking electronic structure, Ir2In8S introduces a new material system to study topological semimetals and enable advances in the field of topological materials.

Electrochemistry of Cd3As2—A 3D Analogue of Graphene

AbstractGraphene has been well‐known for its outstanding electrochemical properties over the years owing to its zero band gap and structural advantages. Lately, Cd3As2, a three‐dimensional (3D) Dirac semi‐metal, has been fervently explored in the field of material physics due to its high electron carrier mobility and transport properties. However, unlike graphene and its derivatives, the electrochemical behavior of Cd3As2 has been underexplored despite it being established as a bulk analogue of 3D graphene in its electronic properties. In this work, we investigate the interesting electrochemistry of Cd3As2 in terms of its heterogeneous electron transfer, as well as its electrocatalytic potential in energy applications like hydrogen evolution reaction.

DNA mediated assembly of single walled carbon nanotubes: role of DNA linkers and annealing

With the high demand for nanoelectronic devices, extensive research has focused on the use of single walled carbon nanotubes (CNTs) due to their high electron carrier mobility, large tensile strength, and single nanometer dimensions. Despite their promise, however, their applicability has been greatly hindered by the inherent difficulties of both separating nanotubes of different chiralities and diameters and positioning them from metallic tubes and positioning them in a precise location on a surface. In recent years, single stranded DNA (ssDNA) has been identified as a potential solution for both of these problems since DNA can be used to both separate the different types of CNTs as well as direct their organization. We demonstrate here the first principles on how to guide CNT assembly directly on surfaces from solution by specific DNA hybridization. It was found that the specific DNA sequence used to disperse the carbon nanotubes greatly influences the adsorption and specificity of nanotube binding to the surface. Furthermore, we demonstrate here that thermal annealing can correct misaligned tubes or incorrect binding. These studies provide an excellent foundation for employing two-dimensional DNA templates for CNT organization for nanoelectronic logic and memory based applications. Furthermore, using a single biomaterial to both sort and place CNTs in minimal steps would greatly help the throughput, manufacturability, and cost of such devices.

Electron Transport and Electrochemistry of Mesomorphic Fullerenes with Long-Range Ordered Lamellae

Fullerenes, C60, modified with long alkyl chains form long-range ordered lamellar mesophases permitting a high C60 content. The mesomorphic fullerenes feature reversible electrochemistry and a comparably high electron carrier mobility making them attractive components for fullerene-based soft materials.

Ultrananocrystalline Diamond Properties and Applications in Biomedical Devices

Diamond is nature’s extreme material. In addition to being the hardest and strongest known substance, diamond is also the best known thermal conductor and possesses very high electron carrier mobility and breakdown fields when in single crystal form. Diamond also exhibits exceptional optical (high refractive index, wide band gap), tribological (low friction), and electrochemical properties that set it apart from other materials either natural or man-made.