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.     

Theoretical design of direct Z-scheme SnC/PtSe2 heterostructure with enhanced photocatalytic performance and tunable optoelectronic properties

Recently, direct Z-scheme heterostructures have attracted much attention because of their outstanding electronic properties and excellent photocatalytic performance. In this article, the electronic, optical and photocatalytic properties of SnC/PtSe₂ heterojunction are systematically explored via first-principles calculations. Evidence suggests that a Type-Ⅱ band alignment as well as an indirect bandgap of 1.35 eV can be observed in the SnC/PtSe₂ heterojunction. The combined influence of the built-in electric field from SnC to PtSe₂ and the band bending causes a Z-scheme carrier migration mechanism. At biaxial strains of −3%–5%, the band edge positions of the heterojunction are able to cross the redox potential of water. The light absorption coefficient of 4.21 × 10⁵ cm⁻¹ and the energy conversion efficiency of 42.32% demonstrate that the photon energy can be utilized by the heterostructure efficiently. Furthermore, the absorption coefficient in the visible range can be significantly increased under tensile strain. Hence, there are reasons to believe that SnC/PtSe₂ heterostructure has tremendous potential for application in the field of photocatalytic water decomposition.     

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.     

二维MoSi2N4WSe2异质结的第一性原理研究

实验上新合成的MoSi2N4（MSN）由于其独特的七原子层结构和电子特性引起了人们的广泛关注。本文搭建了一种由二维MSN与二维WSe2（WS）垂直堆垛而成的二维MSN/WS异质结,其表现出直接间隙半导体和I型能带排列的特性,具有1.46 eV的带隙。在异质结界面处存在一个由电荷耗尽层MSN指向电荷积累层WS微弱的内建电场。最后,通过施加双轴应变对二维MSN/WS异质结进行调控。发现在正双轴应变的作用下,MSN/WS异质结保持了原来直接带隙半导体和I型能带排列特性;在负双轴应变作用下,MSN/WS异质结由原来的直接带隙半导体转变为间接带隙半导体,当施加的负双轴应变达到-6%与-8%时,I型能带排列转变为Ⅱ型能带排列。     

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.     

Two dimensional GeO2/MoSi2N4 van der Waals heterostructures with robust type-II band alignment

Constructing two-dimensional (2D) van der Waals heterostructures (vdWHs) can expand the electronic and optoelectronic applications of 2D semiconductors. However, the work on the 2D vdWHs with robust band alignment is still scarce. Here, we employ a global structure search approach to construct the vdWHs with monolayer MoSi₂N₄ and wide-bandgap GeO₂. The studies show that the GeO₂/MoSi₂N₄ vdWHs have the characteristics of direct structures with the band gap of 0.946 eV and type-II band alignment with GeO₂ and MoSi₂N₄ layers as the conduction band minimum (CBM) and valence band maximum (VBM), respectively. Also, the direct-to-indirect band gap transition can be achieved by applying biaxial strain. In particular, the 2D GeO₂/MoSi₂N₄ vdWHs show a robust type-II band alignment under the effects of biaxial strain, interlayer distance and external electric field. The results provide a route to realize the robust type-II band alignment vdWHs, which is helpful for the implementation of optoelectronic nanodevices with stable characteristics.     

Electronic and optical properties of 3N-doped graphdiyne/MoS2 heterostructures tuned by biaxial strain and external electric field

The construction of van der Waals (vdW) heterostructures by stacking different two-dimensional layered materials have been recognised as an effective strategy to obtain the desired properties. The 3N-doped graphdiyne (N-GY) has been successfully synthesized in the laboratory. It could be assembled into a supercapacitor and can be used for tensile energy storage. However, the flat band and wide forbidden bands could hinder its application of N-GY layer in optoelectronic and nanoelectronic devices. In order to extend the application of N-GY layer in electronic devices, MoS₂ was selected to construct an N-GY/MoS₂ heterostructure due to its good electronic and optical properties. The N-GY/MoS₂ heterostructure has an optical absorption range from the visible to ultraviolet with a absorption coefficient of 10⁵ cm^-1. The N-GY/MoS₂ heterostructure exhibits a type-Ⅱ band alignment allows the electron-hole to be located on N-GY and MoS₂ respectively, which can further reduce the electron-hole complexation to increase exciton lifetime. The power conversion efficiency of N-GY/MoS₂ heterostructure is up to 17.77%, indicating it is a promising candidate material for solar cells. In addition, the external electric field and biaxial strain could effectively tune the electronic structure. Our results provide a theoretical support for the design and application of N-GY/MoS₂ vdW heterostructures in semiconductor sensors and photovoltaic devices.     

Influence of strain and electric field on the properties of silicane

We investigate the influence of strain and electric field on the properties of a silicane sheet. Some elastic parameters of silicane, such as an in-plane stiffness of 52.55 N/m and a Poisson’s ratio of 0.24, are obtained by calculating the strain energy. Compared with silicene, silicane is softer because of its relatively weaker Si-Si bonds. The band structure of silicane is tunable by a uniform tensile strain, with the increase of which the band gap decreases monotonously. Moreover, silicane undergoes an indirect-direct gap transition under a small strain, and a semiconductor-metal transition under a large strain. The electric field can change the Si-H bond length of silicane significantly. When a strong field is applied, the H atom at the high potential side becomes desorbed, while the H atom at the low potential side keeps bonded. So an external electric field can help to produce single-side hydrogenated silicene from silicane. We believe this study will be helpful for the application of silicane in the future.     

Efficient band structure engineering and visible-light response in ZrS2/GaS heterobilayer by electrical field or external strains

Via first-principle methods, the electronic structures and optical properties of 2D ZrS₂/GaS van der Waals heterostructure (vdWH) are studied. It is found that the band alignment changes from type-II to type-I under negative electrical field, and compressive strains. The transition points are -0.2 V/Å and -1%, respectively. The band gap changes efficiently under positive electrical field and compressive strains. The tensile strains increase the optical adsorption coefficients in ultraviolet regions, while the compressive strains increase the optical adsorption coefficients in visible region significantly.     

Strain and electric-field induced tunable electronic properties of blue phosphorus-GeS/SnS/SnSe (orthorhombic) vdW heterostructures

In this work, we composite blue phosphorous (blueP) and monolayer GeS/SnS/SnSe through van der Waals (vdW) force interaction. It is found that blueP-GeS/SnS heterostructures are stable and form type-II band alignments, which can effectively promote the separation of photoinduced carriers. We perform a systematic theoretical study of interlayer coupling effects and band realignment of blueP-GeS/SnS/SnSe heterostructures after the strain and electric-field are imposed. BlueP and GeS/SnS/SnSe are twisted with different angles, and the theoretical framework of bands alignment and carriers' separation are established. The results show that the electronic properties of independent blueP and GeS/SnS/SnSe can be roughly maintained. When strain is applied, the band alignment shows significant adjustability by changing the external strain. Besides, the blueP-SnSe heterostructure show type-II characteristic in the range from -0.25 V/Å to -0.1 V/Å. Our theoretical calculation proves that strain and electric field engineering are two useful methods to design novel electronic devices.     

Prediction of quantum anomalous Hall effect in CrI3/ScCl2 bilayer heterostructure

Based on first-principles calculations, a two-dimensional (2D) van der Waals (vdW) bilayer heterostructure consisting of two topologically trivial ferromagnetic (FM) monolayers CrI₃ and ScCl₂ is proposed to realize the quantum anomalous Hall effect (QAHE) with a sizable topologically nontrivial band gap of 4.5 meV. Its topological nature is attributed to an interlayer band inversion between the monolayers and critically depends on the symmetry of the stacking configuration. We further demonstrate that the topologically nontrivial band gap can be increased nearly linearly by the application of a perpendicular external pressure and reaches 8.1 meV at 2.7 GPa, and the application of an external out-of-plane electric field can also modulate the band gap and convert the system back to topologically trivial via eliminating the band inversion. An effective model is developed to describe the topological phase evolution in this bilayer heterostructure. This work provides a new candidate system based on 2D vdW materials for realization of potential high-temperature QAHE with considerable controllability.     

电场调控双层石墨烯纳米带的电子结构和光学性质

利用基于密度泛函理论的第一性原理方法,研究了外加电场作用下双层AA堆垛的Armchair边缘石墨烯纳米带(BAGNRs)的电子结构和光学性质. BAGNRs具有半导体特性,其带隙随带宽(宽度为4～12个碳原子)的增加而振荡性减小.当施加电场后,BAGNRs的带隙随着电场强度的增加而逐渐减小,带隙越大对电场值的变化越敏感.当电场值为0.5 V/?时,所有BAGNRs的带隙都为零. BAGNRs具有各向异性的光学性质,其介电函数在垂直极化方向为半导体特性,而在平行极化方向为金属特性.在外加电场的作用下,BAGNRs的介电函数、吸收系数、折射系数、反射系数、电子能量损失系数和光电导率,其峰值向低能量区域移动,即产生红移现象.电场增强了能带间的跃迁几率.纳米带宽度对这些光学性质参数具有不同程度的影响.研究结果解释了电场调控BAGNRs光学性质的规律和微观机理.     

电场对PtO2/MoS2范德瓦尔斯异质结电子结构调控

本文利用基于密度泛函理论的第一性原理计算方法研究了外电场对PtO2/MoS2范德瓦尔斯异质结电子结构的调控,发现当层间距d=2.83Å时异质结结构最稳定,且表现为Ⅱ型间接带隙半导体,其带隙为0.68 eV。通过施加垂直平面方向电场可有效调控PtO2/MoS2异质结电子结构,当外电场为-1 V/Å时,发生半导体-金属相变。这些研究结果表明PtO2/MoS2异质结在新型二维材料光电纳米器件方面具有广泛应用前景。     

应力调控BlueP/XTe2(X=Mo,W)范德瓦耳斯异质结电子结构及光学性质理论研究

通过第一性原理计算探讨了蓝磷烯与过渡金属硫化物MoTe₂/WTe₂形成范德瓦耳斯异质结的电子结构和光学性质,以及施加双轴应力对相关性质的影响.计算结果表明,形成BlueP/XTe₂(X=Mo,W)异质结,二者能带排列为间接带隙type-Ⅱ并有较强的红外光吸收,同时屏蔽特性增强.随压缩应力增加,BlueP/XTe₂转变为直接带隙type-Ⅱ能带排列最后转变为金属性;随拉伸应力增加,异质结转变为间接带隙type-Ⅰ能带排列.外加应力也能有效调控异质结的光吸收性质,随压缩应力增加吸收边红移,光吸收响应拓展至中红外光谱区且吸收系数增大;BlueP/MoTe₂较BlueP/WTe₂在中红外至红外光区间表现出更强的光吸收响应;静态介电常数ε1(0)大幅增加.结果表明,压缩应力对BlueP/MoTe₂和BlueP/WTe₂能带排列、光吸收特性均有显著的调控作用,其中BlueP/MoTe₂对调控更敏感,这些特性也使BlueP/XTe₂异质结在窄禁带中红外半导体材料及光电器件具有令人期待的应用价值.     

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.     

Modulation of strain,electric field and organic cation rotation on the band gap and electronic structures of organic-inorganic hybrid perovskite CH3NH3PbI3

Band gap modulation engineering is an important step in the application of optoelectronic materials. In this paper, the first-principles calculations were carried out to study the influence of strain, external electric field, spatial orientation of organic cation on the band gaps and electronic structures of organic-inorganic hybrid halide perovskites CH₃NH₃PbI₃. The results show that both the uniform strain and the tetragonal deformation can modulate the band gap obviously. The electric field of 0.2 V/Å is the critical point of the band gap modulation. The band gap increases when an electric field is applied from 0 to 0.2 V/Å. The electric field above 0.2 V/Å will cause the band gap to decrease. The spatial orientation of the organic cation also has modulation influence on the band gap of CH₃NH₃PbI₃, but has no effect on the direct semiconductor characteristics. The above results will be helpful to study the band gap modulation of other organic-inorganic hybrid halide perovskites.     

Effects of an electric field on the electronic and optical properties of zigzag boron nitride nanotubes

We have investigated the electro-optical properties of zigzag BNNTs, under an external electric field, using the tight binding approximation. It is found that an electric field modifies the band structure and splits the band degeneracy. Also the large electric strength leads to coupling the neighbor subbands which these effects reflect in the DOS and JDOS spectrum. It has been shown that, unlike CNTs, the band gap of BNNTs can be reduced linearly by applying a transverse external electric field. Also we show that the larger diameter tubes are more sensitive than small ones. The semiconducting metallic transition can be achieved through increasing the applied fields. The number and position of peaks in the JDOS spectrum are dependent on electric field strength. It is found that at a high electric field, the two lowest subbands are oscillatory with multiple nodes at the Fermi level.     

Interlayer coupling effect in van der Waals heterostructures of transition metal dichalcogenides

Van der Waals(vdW)heterobilayers formed by two-dimensional(2D)transition metal dichalcogenides(TMDCs)created a promising platform for various electronic and optical properties,ab initio band results indicate that the band offset of type-Ⅱband alignment in TMDCs vdW heterobilayer could be tuned by introducing Janus WSSe monolayer,instead of an external electric field.On the basis of symmetry analysis,the allowed interlayer hopping channels of TMDCs vdW heterobilayer were determined,and a four-level k·p model was developed to obtain the interlayer hopping.Results indicate that the interlayer coupling strength could be tuned by interlayer electric polarization featured by various band offsets.Moreover,the difference in the formation mechanism of interlayer valley excitons in different TMDCs vdW heterobilayers with various interlayer hopping strength was also clarified.     

Strain drived band aligment transition of the ferromagnetic VS_2/C_3N van der Waals heterostructure

Exploring two-dimensional(2 D) magnetic heterostructures is essential for future spintronic and optoelectronic devices.Herein,using first-principle calculations,stable ferromagnetic ordering and colorful electronic properties are established by constructing the VS_2/C_3 N van der Waals(vdW) heterostructure.Unlike the semiconductive properties with indirect band gaps in both the VS_2 and C_3 N monolayers,our results indicate that a direct band gap with type-Ⅱ band alignment and p-doping characters are realized in the spin-up channel of the VS_2/C_3 N heterostructure,and a typical type-Ⅲband alignment with a broken-gap in the spin-down channel.Furthermore,the band alignments in the two spin channels can be effectively tuned by applying tensile strain.An interchangement between the type-Ⅱ and type-Ⅲ band alignments occurs in the two spin channels,as the tensile strain increases to 4%.The attractive magnetic properties and the unique band alignments could be useful for prospective applications in the next-generation tunneling devices and spintronic devices.     

光控光子晶体偏光片

提出了一种新颖的调节液晶光子晶体光子带隙的方法.光子晶体波导通过往二维三角形光子晶体的介质柱之间填充液晶得到，光诱导液晶取向以改变液晶的折射指数从而改变光子晶体的光子带隙.数值模拟结果表明：通过外界光场控制所填充的向列相液晶的方向可以对这种二维三角形介质柱光子晶体的禁带结构进行调节.与电场调制方法相比，该光控液晶取向技术具有响应速度快、结构简单的优点.这种可调光子晶体可用于制作新颖的光敏偏光片.