The unique carrier mobility of Janus MoSSe/GaN heterostructures

Heterostructure is an effective approach in modulating the physical and chemical behavior of materials. Here, the first-principles calculations were carried out to explore the structural, electronic, and carrier mobility properties of Janus MoSSe/GaN heterostructures. This heterostructure exhibits a superior high carrier mobility of 281.28 cm²·V⁻¹·s⁻¹ for electron carrier and 3951.2 cm²·V⁻¹·s⁻¹ for hole carrier. Particularly, the magnitude of the carrier mobility can be further tuned by Janus structure and stacking modes of the heterostructure. It is revealed that the equivalent mass and elastic moduli strongly affect the carrier mobility of the heterostructure, while the deformation potential contributes to the different carrier mobility for electron and hole of the heterostructure. These results suggest that the Janus MoSSe/GaN heterostructures have many potential applications for the unique carrier mobility.     

Strain-tunable electronic and optical properties of h-BN/BC_3 heterostructure with enhanced electron mobility

By using first-principles calculation, we study the properties of h-BN/BC_3 heterostructure and the effects of external electric fields and strains on its electronic and optical properties. It is found that the semiconducting h-BN/BC_3 has good dynamical stability and ultrahigh stiffness, enhanced electron mobility, and well-preserved electronic band structure as the BC_3 monolayer. Meanwhile, its electronic band structure is slightly modified by an external electric field. In contrast,applying an external strain can mildly modulate the electronic band structure of h-BN/BC_3 and the optical property exhibits an apparent redshift under a compressive strain relative to the pristine one. These findings show that the h-BN/BC_3 hybrid can be designed as optoelectronic device with moderately strain-tunable electronic and optical properties.     

Tunable electronic properties of GaS-SnS2 heterostructure by strain and electric field

Vertically stacked heterostructures have received extensive attention because of their tunable electronic structures and outstanding optical properties. In this work, we study the structural, electronic, and optical properties of vertically stacked GaS-SnS₂ heterostructure under the frame of density functional theory. We find that the stacked GaS-SnS₂ heterostructure is a semiconductor with a suitable indirect band gap of 1.82 eV, exhibiting a type-II band alignment for easily separating the photo-generated carriers. The electronic properties of GaS-SnS₂ heterostructure can be effectively tuned by an external strain and electric field. The optical absorption of GaS-SnS₂ heterostructure is more enhanced than those of the GaS monolayer and SnS₂ monolayer in the visible light region. Our results suggest that the GaS-SnS₂ heterostructure is a promising candidate for the photocatalyst and photoelectronic devices in the visible light region.     

Tunable electronic and optical properties of SnC/BAs heterostructure by external electric field and vertical strain

Based on the first-principles method, we investigate the electronic structure of SnC/BAs van der Waals (vdW) heterostructure and find that it has an intrinsic type-II band alignment with a direct band gap of 0.22 eV, which favors the separation of photogenerated electron–hole pairs. The band gap can be effectively modulated by applying vertical strain and external electric field, displaying a large alteration of band gap via the strain and experiencing an indirect-to-direct band gap transition. Moreover, the band gap of the heterostructure varies almost linearly with external electric field, and the semiconductor-to-metal transition can be realized in the presence of a strong electric field. The calculated band alignment and the optical absorption reveal that the SnC/BAs heterostructure could present an excellent light-harvesting performance. Our designed heterostructure is expected to have great potential applications in nanoelectronic devices and photovoltaics and optical properties.     

二硫化钨/石墨烯异质结的界面相互作用及其肖特基调控的理论研究

采用第一性原理方法研究了二硫化钨/石墨烯异质结的界面结合作用以及电子性质,结果表明在二硫化钨/石墨烯异质结中,其界面相互作用是微弱的范德瓦耳斯力.能带计算结果显示异质结中二硫化钨和石墨烯各自的电子性质得到了保留,同时,由于石墨烯的结合作用,二硫化钨呈现出n型半导体.通过改变界面的层间距可以调控二硫化钼/石墨烯异质结的肖特基势垒类型,层间距增大,肖特基将从p型转变为n型接触.三维电荷密度差分图表明,负电荷聚集在二硫化钨附近,正电荷聚集在石墨烯附近,从而在界面处形成内建电场.肖特基势垒变化与界面电荷流动密切相关,平面平均电荷密度差分图显示,随着层间距逐渐增大,界面电荷转移越来越弱,且空间电荷聚集区位置向石墨烯层方向靠近,导致费米能级向上平移,证实了肖特基势垒随着层间距的增加由p型接触向n型转变.本文的研究结果将为二维范德瓦耳斯场效应管的设计与制作提供指导.     

Monolayered semiconducting GeAsSe and SnSbTe with ultrahigh hole mobility

High carrier mobility and a direct semiconducting band gap are two key properties of materials for electronic device applications. Using first-principles calculations, we predict two types of two-dimensional semiconductors, ultrathin GeAsSe and SnSbTe nanosheets, with desirable electronic and optical properties. Both GeAsSe and SnSbTe sheets are energetically favorable, with formation energies of −0.19 and −0.09 eV/atom, respectively, and have excellent dynamical and thermal stability, as determined by phonon dispersion calculations and Born–Oppenheimer molecular dynamics simulations. The relatively weak interlayer binding energies suggest that these monolayer sheets can be easily exfoliated from the bulk crystals. Importantly, monolayer GeAsSe and SnSbTe possess direct band gaps (2.56 and 1.96 eV, respectively) and superior hole mobility (~20 000 cm²·V⁻¹·s⁻¹), and both exhibit notable absorption in the visible region. A comparison of the band edge positions with the redox potentials of water reveals that layered GeAsSe and SnSbTe are potential photocatalysts for water splitting. These exceptional properties make layered GeAsSe and SnSbTe promising candidates for use in future high-speed electronic and optoelectronic devices.     

Electronic and optical properties of black phosphorus doped with Au,Sn and I atoms

In this study, the electronic and the optical properties of monolayer black phosphorus (BP) doped with Gold (Au), Tin (Sn) and Iodine (I) atoms have been investigated by the density-functional theory (DFT) method. In the calculations, the electronic and the optical properties of monolayer BP have been substantially changed with doping. Monolayer BP has a narrow bandgap as 0.85 eV, BP doped with these atoms, results in a metallic behaviour and nearly spin gapless band gap behaviour. The dielectric constant of BP which shows anisotropic optical properties due to different edge states as zigzag and armchair has been changed with doping especially with Au.     

Electronic and optical properties of an intrinsic type-I band alignment ZrS_2/SnS_2 van der Waals heterostructure for optoelectronic devices

The electronic and optical properties of the ZrS_2/SnS_2 van der Waals heterostructure have been investigated.We find out that the formed heterostructure has an intrinsic type-I band alignment. Moreover, the characteristics of optical absorption in the heterostructure can be enhanced to the amount of 106 in the ultraviolet light region. In addition, the tuning electronic properties of ZrS_2/SnS_2 heterostructure are very interesting, due to the transitions from type-I to type-II band alignment that can occur by applying an external electric field.These results suggest that the atomically thin materials ZrS_2/SnS_2 heterostructure will be utilized for flexible optoelectronic applications.     

Investigation of electronic property modulation driven by strain in monolayer tellurium

Density functional theory (DFT) calculations have been employed to systematically investigate the strain-modulated electronic properties of monolayer tellurium. The results demonstrate that at zero strain γ-phase monolayer tellurium is found to be more energetically favorable than either the α-phase or β-phase which were fabricated through molecular-beam epitaxy. All studied phases are found to exhibit semiconductor characteristics, of which α- and γ-phases possess indirect band gaps whereas β phase is a direct band gap semiconductor. It is also found that the resulting band gap values approach zero at a large strain regime for all systems and the effective mass of electron and hole can be effectively modified by biaxial strain as well. These findings extend the knowledge on two-dimensional tellurium and provide potential applications in electronic devices.     

Ce、Ga、La掺杂二维SnO2电子结构及光电性质的第一性原理研究

二维材料具有优异的光学、力学、热学、磁学等性质,成为研究的热点之一. SnO₂薄膜中的电子迁移率非常高,兼具透明和良好的导电性能,是一种性能绝佳的半导体材料.本文用密度泛函理论框架下的第一性原理研究了二维SnO₂及其掺杂体系的电子结构、电子态密度、导电性能及光学性质,计算结果表明：相比较于三维SnO₂,二维SnO₂的费米能级附近产生很多杂质能级,提高了载流子浓度,带隙明显变窄,电子的局域性增强,导带中电子的有效质量增加了,电子跃迁更容易发生,增加了材料的导电性能;二维SnO₂比三维SnO₂材料的电极化能力强,在红外区、可见光区、紫外区域的光子吸收性能更优异,光电导率更高,更有利于光生电子-空穴对的分离和迁移,即可以有效地提高其光电转换效率,其中掺杂La元素能更好地提高在红外区、可见光区及紫外区吸收光子的能力,更有利于光电转换的效率,提高导电性.     

First-principles hybrid functional study of the electronic structure and charge carrier mobility in perovskite CH_3NH_3SnI_3

We calculate the electronic properties and carrier mobility of perovskite CH_3NH_3SnI_3 as a solar cell absorber by using the hybrid functional method. The calculated result shows that the electron and hole mobilities have anisotropies with a large magnitude of 1.4 × 10~4cm~2·V~(-1)·s~(-1) along the y direction. In view of the huge difference between hole and electron mobilities, the perovskite CH3NH3 Sn I3can be considered as a p-type semiconductor. We also discover a relationship between the effective mass anisotropy and electronic occupation anisotropy. The above results can provide reliable guidance for its experimental applications in electronics and optoelectronics.     

三唑和环戊烯苯并菲衍生物盘状液晶分子的电荷传输性质

电荷传输是有机电子材料的重要性质. 根据Marcus理论模型, 电荷传输为电子-电子相互作用和电子-声子相互作用过程, 电子-声子相互作用耦合强度越大, 重组能越大, 不利于电荷传输. 电子-电子相互作用耦合强度越大, 电荷传输矩阵元越大, 有利于电荷传输. 对含1, 2, 4-三唑、1, 2, 3-三唑和1, 2, 3-三氮-2, 3环戊烯边链的苯并菲衍生物分子的电荷传输性质进行理论研究. 结果表明, 含1, 2, 3-三唑的苯并菲衍生物分子的空穴传输速率和电子传输速率相当, 速率常数为2× 10¹²s^-1. 含1, 2, 4-三唑的苯并菲衍生物分子的空穴传输速率常数为5× 10¹²s^-1, 约为电子传输速率常数的10倍. 含1, 2, 3-三氮-2, 3环戊烯的苯并菲衍生物分子的电子传输速率常数为3× 10¹²s^-1, 约为空穴传输速率常数的10倍. 目标分子的空穴传输或电子传输速率主要受传输矩阵元的影响, 即电子-电子相互作用耦合强度的大小决定传输速率的变化.     

TiS2-graphene heterostructures enabling polysulfide anchoring and fast electrocatalyst for lithium-sulfur batteries: A first-principles calculation

Lithium-sulfur batteries have attracted attention because of their high energy density. However, the "shuttle effect" caused by the dissolving of polysulfide in the electrolyte has greatly hindered the widespread commercial use of lithium-sulfur batteries. In this paper, a novel two-dimensional TiS₂/graphene heterostructure is theoretically designed as the anchoring material for lithium-sulfur batteries to suppress the shuttle effect. This heterostructure formed by the stacking of graphene and TiS₂ monolayer is the van der Waals type, which retains the intrinsic metallic electronic structure of graphene and TiS₂ monolayer. Graphene improves the electronic conductivity of the sulfur cathode, and the transferred electrons from graphene enhance the polarity of the TiS₂ monolayer. Simulations of the polysulfide adsorption show that the TiS₂/graphene heterostructure can maintain good metallic properties and the appropriate adsorption energies of 0.98-3.72 eV, which can effectively anchor polysulfides. Charge transfer analysis suggests that further enhancement of polarity is beneficial to reduce the high proportion of van der Waals (vdW) force in the adsorption energy, thereby further enhancing the anchoring ability. Low Li₂S decomposition barrier and Li-ion migration barrier imply that the heterostructure has the ability to catalyze fast electrochemical kinetic processes. Therefore, TiS₂/graphene heterostructure could be an important candidate for ideal anchoring materials of lithium-sulfur batteries.     

Electronic structures and optical absorption of multilayer graphenes

We study the electronic structures and the optical absorption spectra of the multilayer graphenes in the effective mass approximation. We decompose the Hamiltonian of graphene with an arbitrary thickness into smaller subsystems effectively identical to monolayer or bilayer graphene, and express the optical spectrum as a summation over the subsystems. We include the full band parameters which compose the bulk graphite, and closely study their effects on the band structure. We found that the particular band parameters destroying the electron–hole symmetry can affect the optical spectrum through shift of the absorption edge.     

(Cu,N)共掺杂TiO2/MoS2异质结的电子和光学性能:杂化泛函HSE06

在密度泛函理论的基础上,系统地研究了Cu/N（共）掺杂的TiO₂/MoS₂异质结体系的几何结构、电子结构和光学性质.计算发现,TiO₂/MoS₂异质结的带隙相比于纯的TiO₂（101）表面明显变小,Cu/N（共）掺杂TiO₂/MoS₂异质结体系的禁带宽度也明显地减小,这导致光子激发能量的降低和光吸收能力的提高.通过计算Cu/N（共）掺杂TiO₂/MoS₂的差分电荷密度,发现光生电子与空穴积累在掺杂后的TiO₂（101）表面和单层MoS₂之间,这表明掺杂杂质体系可以有效地抑制光生电子-空穴对的复合.此外,我们计算了在不同压力下TiO₂/MoS₂异质结的几何、电子和光学性质,发现适当增加压力可以有效提高异质结的光吸收性能.本文结果表明,Cu/N（共）掺杂TiO₂/MoS₂异质结和对TiO₂/MoS₂异质结加压都能有效地提高材料的光学性能.     

Isotropic or anisotropic screening in black phosphorous: Can doping tip the balance?

Black phosphorus (BP), a layered van der Waals (vdW) crystal, has unique in-plane band anisotropy and many resulting anisotropy properties such as the effective mass, electron mobility, optical absorption, thermal conductivity and plasmonic dispersion. However, whether anisotropic or isotropic charge screening exist in BP remains a controversial issue. Based on first-principles calculations, we study the screening properties in both of single-layer and bulk BP, especially concerning the role of doping. Without charge doping, the single-layer and bulk-phase BP show slight anisotropic screening. Electron and hole doping can increase the charge screening of BP and significantly change the relative static dielectric tensor elements along two different in-plane directions. We further study the charge density change induced by potassium (K) adatom near the BP surface, under different levels of charge doping. The calculated two-dimensional (2D) charge redistribution patterns also confirm that doping can greatly affect the screening feature and tip the balance between isotropic and anisotropic screening. We corroborate that screening in BP exhibits slight intrinsic anisotropy and doping has significant influence on its screening property.     

硫化锡电子结构和光学性质的量子尺寸效应

基于密度泛函理论的第一性原理计算,系统研究了硫化锡(SnS)晶体、纳米单层及多层的结构稳定性、电子结构和光学性质.结果表明:由于相对弱的层间范德瓦尔斯力作用,SnS单层纳米片可以像石墨烯等二维材料一样从块体中剥离出来;受制于量子尺寸效应和层间相互作用的影响,SnS的结构稳定性随层数减少而逐渐减弱,其带隙随层数减少而逐渐增大;由于材料的本征激发和吸收取决于电子结构,因此改变SnS材料的层数可以到达调控其光学性质的目的;SnS块体和纳米结构的主要光学吸收峰起源于Sn-5s,5p和S-2p轨道之间的电子跃迁;并且从块体到单层纳米结构,SnS的光学吸收峰出现明显的蓝移.本文的研究将有助于SnS材料在太阳能电池领域的应用.     

二维6H-SiC光学特性的应变调控

为了减小6H-SiC的带隙、提高对可见光的吸收效率和载流子迁移速率,采用第一性原理研究了应变对6H-SiC的能带结构、光学吸收系数、载流子迁移率以及光催化特性的影响。结果表明：应变能够降低6H-SiC的导带底,但对价带顶没有影响,导致带隙减小。随着应变的增加,吸收曲线向低能级方向移动,即发生红移,有利于可见光的吸收。施加应变后空穴的载流子迁移率提高,有利于载流子移动,且空穴的载流子迁移率是电子的2.5倍,有利于空穴和电子的分离。综合应变对带隙大小、带边位置的影响可知,应变在±2%、±4%时对可见光的吸收以及光催化制氢最有效。综上所述,应变能够对6H-SiC的光学吸收和光催化特性有很好的调控作用。     

二维GaTe/Bi2Se3异质结：一类有潜力的Z型光解水催化剂

本文基于第一性原理方法,计算了二维GaTe/Bi₂Se₃异质结的电子结构、界面电荷转移、静电势分布、吸收光谱及光催化性质. 计算结果表明异质结是一个小能隙的准直接半导体,能有效捕获太阳光. 由于相对较强的界面內建极化电场和带边轻微弯曲,导致异质结中的光生电子和空穴分别有效分离在GaTe单层和Bi₂Se₃薄片上,可用于析氢和产氧. 这些理论计算结果意味着二维GaTe/Bi₂Se₃异质结是一类有潜力的Z型太阳能全解水催化剂.     

Stress and strain effects on the electronic structure and optical properties of ScN monolayer

Based on the density functional theory, electronic and optical properties of a monolayer scandium nitride structure have been studied under different strain conditions. Our results indicate that both biaxial compressive and tensile strain effects lead to change the band gap of this structure with different rates. Also, optical absorption spectrum peaks experience an obvious red and blue shifts with the exerting of tensile and compressive strains, respectively. Our results express that ScN monolayer can be the promising candidate for the future nano-base electrical and optical devices.