Direct Band Gap Semiconductor Research Articles

Electronic Structure Analysis of the A10 Tt2 P6 System (A=Li-Cs; Tt=Si, Ge, Sn) and Synthesis of the Direct Band Gap Semiconductor K10 Sn2 P6.

Investigating the relationship between atomic and electronic structures is a powerful tool to screen the wide variety of Zintl phases for interesting (opto-)electronic properties. To get an insight in such relations, the A10 Tt2 P6 system (A=Li-Cs; Tt=Si-Sn) was picked as model system to analyse the influence of structural motives, combination of elements and their properties on type and width of the band gaps. Those compounds comprise two interesting structural motives of their anions, which are either monomeric trigonal planar TtP3 5- units which are isostructural to CO3 2- or [Tt2 P6 ]10- dimers which correspond to two edge-sharing TtP4 tetrahedra. The A10 Tt2 P6 compounds were structurally optimized for both polymorphs and subsequent frequency analysis, band structure as well as density of states calculations were performed. The Gibbs free energies were compared to determine temperature dependent stability, where Na10 Si2 P6 , Na10 Ge2 P6 and K10 Sn2 P6 were found to be candidates for a high temperature phase transition between the two polymorphs. Additionally, the unknown, but predicted compound K10 Sn2 P6 was synthesized and characterized by single crystal and powder x-ray diffraction. It crystalizes in the monoclinic space group P 21 /n and incorporates [Sn2 P6 ]10- edge sharing double tetrahedra. It was determined to be a direct band gap semiconductor with a band gap of 2.57 eV.

Bending deformation modulation of the optoelectronic properties of molybdenum ditelluride doped with nonmetallic atoms X (X = B, C, N, O): a first-principles study.

A first-principles approach based on density functional theory was used to explore the effect of bending deformation on the electrical structure of molybdenum ditelluride doped with nonmetallic atoms X (X = B, C, N, and O). The study included alternate doping of nonmetallic atoms, as well as a comparison of the effects of intrinsic bending deformation and nonmetallic doping deformation. The results demonstrate that boron atom doping raises the Fermi energy level. Examining the energy band structure indicates that the intrinsic molybdenum ditelluride is a direct band gap semiconductor, which is transformed from a direct band gap to an indirect band gap after doping. We selected boron-doped systems for bending deformation and compared them with the intrinsic systems. With increasing deformation, all systems start to shift from semiconductor to metal. When the deformation reaches 8°, the energy levels fill and the electron energy increases. The intrinsically bent systems transition from direct band gap to indirect band gap and eventually to metal. The indirect band gap semiconductor-to-metal transition process occurs after the bending deformation of the boron-doped atoms. The analytical results show that the absorption and reflection peaks of the molybdenum ditelluride system are blue-shifted after the bending deformation of the boron-doped atoms. Under fundamental principles, this research depends on the density functional theory framework (DFT) using the CASTEP module in the Materials-Studio software. The plane-wave pseudopotential approach with modified gradient approximation and the Perdew-Burke-Ernzerhof (PBE) generalized function is used for structure optimization and total energy calculations of the X-doped (X = B, C, N, O) MoTe2 system at different shape variables. Geometry optimization of the 27-atom superlattice MoTe2 was carried out, followed by alternative doping of tellurium atoms in the molybdenum ditelluride with B, C, N, and O. In this paper, the intrinsic bending deformation and B-doping of molybdenum ditelluride were selected for deformation analysis. Intrinsic bending deformations and boron-doped molybdenum ditelluride with bending angles ranging from 2° to 8° were employed for deformation investigation. In Fig.1, pink is used to represent doped B atoms, orange is used to describe Te atoms, and green is used to represent Mo atoms. For the degree of deformation of molybdenum ditelluride, in this paper, it is expressed by the bending angle, i.e., the angle of the plane of molybdenum ditelluride after bending and deformation of a single layer of molybdenum ditelluride concerning the angle of the plane folded for the deformed plane. How to do it: For ease of presentation, the atomic chains are set to different colors. The purple part on both sides of the figure is bent and deformed, 3-5 atoms are fixed appropriately, and the middle part is deformed. On this basis, the bending deformation of intrinsically doped and boron-doped MoTe2 is comparatively analyzed. The effect of boron-doped atoms on the structure of MoTe2 is systematically investigated to study its structural stability and electronic structure. Fig.1 a1 and a2 The main and side views of intrinsic MoTe2; b1 and (b2) the main and side views of MoTe2 doped with boron atoms bent by 8°.

Rational Design of Tetrahedral Derivatives as Efficient Light-Emitting Materials Based on "Super Atom" Perspective.

Traditional semiconductor quantum dots of groups II-VI are key ingredients of next-generation display technology. Yet, the majority of them contain toxic heavy-metal elements, thus calling for alternative light-emitting materials. Herein, we have explored three novel categories of multicomponent compounds, namely, tetragonal II-III2-VI4 porous ternary compounds, cubic I2-II3-VI4 ternary compounds, and cubic I-II-III3-V4 quaternary compounds. This is achieved by judicious introduction of a "super atom" perspective and concurrently varying the solid-state lattice packing of involved super atoms or the population of surrounding counter cations. Based on first-principles calculations of 392 candidate materials with designed crystal structures, 53 highly stable materials have been screened. Strikingly, 34 of them are direct-bandgap semiconductors with emitting wavelengths covering the near-infrared and visible-light regions. This work provides a comprehensive database of highly efficient light-emitting materials, which may be of interest for a broad field of optoelectronic applications.

Effect of tensile deformation on the optoelectronic properties of black phosphine-doped lithium atoms.

First-principles calculations based on the generalized gradient approximation gradient and the Perdew-Burke-Ernzerhof function (GGA-PBE generalized function) are carried out on the intrinsic and lithium-doped black phosphine systems to investigate the effects of different uniaxial tensile deformations on the electronic and optical properties of the systems. It is shown that the structural stability of the intrinsic and lithium-doped systems decreases with increasing tensile deformation, and all systems are most stable at 0% tensile deformation. The intrinsic black phosphazene system is a direct band gap semiconductor, and its band gap increases and then decreases with tensile deformation and reaches a maximum value of 1.086eV at 4%. Lithium doping closes the band gap of the black phosphazene system, which is metallic in nature, but the band gap is opened up when the tensile deformation is 4-6%. From the density of states analysis, the density of states of all systems is basically contributed by the s and p orbitals, with little contribution from the d orbitals, and the contribution from the p orbitals is dominant. From the analysis of optical properties, the increase of tensile deformation causes the absorption peaks of the intrinsic system to redshift then blueshift then redshift, causes the absorption peaks of the lithium-doped system to redshift, and causes the reflection peaks of all systems to redshift. In addition, lithium doping blueshifts the absorption and reflection peaks of the systems compared to the intrinsic black phosphazene system. Using the CASTEP section of the Materials Studio software, first-principle calculations based on density functional theory are done on the top-site doped lithium atoms of monolayer black phosphine under uniaxial stretching deformation in the a-direction, and the generalized gradient approximation gradients and Perdew-Burke-Ernzerhof functions (GGA-PBE generalized functionals) are used for the optimization and approximation process. The optimization parameters are set for the supercell structure: its plane-wave truncation energy is set to 400eV, its Brillouin zone K-point grid is set to 3*3*3, its self-consistent field iteration accuracy convergence value is 2.0e-6eV/atom, the convergence basis of its structural optimization is 0.02eV/ Å, and the convergence of the stress value is 0.05 gpa. During the optimization period, the interaction force between atoms is 0.03eV/ Å and the atomic displacement is less than 0.001Å. To eliminate the effect of interlayer forces, a vacuum layer with a thickness of 15Å is placed in its vertical direction (i.e., c-axis direction).

Study of electronic structure, elastic and thermodynamic properties of Cu2MgSnS4 under different pressures

The electronic structure, elastic and thermodynamic properties of Cu2MgSnS4 was studied based on density functional theory (DFT). The results show that Cu2MgSnS4 is a direct bandgap semiconductor. The B/G of Cu2MgSnS4 is greater than 1.75, indicating that Cu2MgSnS4 is a ductile material. Through the study of thermodynamic properties, it is found that the temperature increases, the bulk modulus B and Debye temperature Θ decrease, while the heat capacity CV, entropy S, Grüneisen constant γ and thermal expansion coefficient α increase, and the heat capacity is close to the Dulong-Petit limit. As the pressure increases, the bulk modulus B, Debye temperature Θ increases, while the entropy S, Grüneisen constant γ and heat capacity CV decrease.

Lead-free alternative cation (Ethylammonium) in organometallic perovskites for thermoelectric applications.

Hybrid halide perovskites are gaining prominence as a promising option in the advancement of photovoltaic devices. Ethylammonium-based hybrid halide perovskites have demonstrated impressive characteristics, such as a reduced band gap, enhanced stability, and non-toxic properties. In this study, we have explored the structural, electronic, optical, and thermoelectric characteristics of Ethylammonium tin chloride. We have found that Ethylammonium tin chloride (EASnCl3) is a direct wide band gap semiconductor. Additionally, we conducted calculations for various optical parameters, including the dielectric function, absorption coefficient, and refractive index, across a photon energy spectrum ranging from 0 to 7eV. The research highlights the exceptional qualities of EASnCl3, which exhibits a high absorption coefficient and an elevated Seeback coefficient, among other favorable attributes. These findings position it as a promising material for cost-effective photovoltaic device applications, addressing concerns related to environmental stability. Fundamental properties based on the full-potential linearized augmented plane wave (FP-LAPW) method, this computation was performed using the WIEN2k simulation code. We utilized the exchange-correlation potentials PBE-GGA and KTB-mBJ to compute the optimized structure, density of states, and band structure of the material. In order to calculate the thermoelectric properties of the material, the Boltztrap simulation tool has been used. There are several critical absorbance parameters, including the Seeback coefficient, figure of merit, power factor, electrical conductivity, and thermal conductivity, concerning their carrier concentration and chemical potential, that have been taken into consideration.

Ultrafast Q-boosting in semiconductor metasurfaces

Abstract All-optical tunability of semiconductor metasurfaces offers unique opportunities for novel time-varying effects, including frequency conversion and light trapping. However, the all-optical processes often induce optical absorption that fundamentally limits the possible dynamic increase of their quality factor (Q-boosting). Here, we propose and numerically demonstrate the concept of large Q-boosting in a single-material metasurface by dynamically reducing its structural anisotropy on a femtosecond timescale. This balance is achieved by excitation with a structured pump and takes advantage of the band-filling effect in a GaAs direct-bandgap semiconductor to eliminate the free-carrier-induced loss. We show that this approach allows a dynamic boosting of the resonance quality factor over orders of magnitude, only limited by the free-carrier relaxation processes. The proposed approach offers complete dynamic control over the resonance bandwidth and opens applications in frequency conversion and light trapping.

Direct Band Gap Semiconductors with Two- and Three-Dimensional Triel-Phosphide Frameworks (Triel=Al, Ga, In).

Recently, several ternary phosphidotrielates and -tetrelates have been investigated with respect to their very good ionic conductivity, while less focus was pointed towards their electronic structures. Here, we report on a novel series of compounds, in which several members possess direct band gaps. We investigated the known compounds Li3AlP2, Li3GaP2, Li3InP2, and Na3InP2 and describe the synthesis and the crystal structure of novel Na3In2P3. For all mentioned phosphidotrielates reflectance UV-Vis measurements reveal direct band gaps in the visible light region with decreasing band gaps in the series: Li3AlP2 (2.45 eV), Li3GaP2 (2.18 eV), Li3InP2 (1.99 eV), Na3InP2 (1.37 eV), and Na3In2P3 (1.27 eV). All direct band gaps are confirmed by quantum chemical calculations. The unexpected property occurs despite different structure types. As a common feature all compounds contain EP4 tetrahedra, which share exclusively vertices for E=In and vertices as well as edges for E=Al and Ga. The structure of the novel Na3In2P3 is built up by a polyanionic framework of six-membered rings of corner-sharing InP4 tetrahedra. As a result, the newly designed semiconductors with direct band gaps are suitable for optoelectronic applications, and they can provide significant guidance for the design of new functional semiconductors.

Electronic, optical, and thermoelectric properties of vacancy-ordered double perovskite K2SnX6 (X = Cl, Br, I) from first-principle calculations

Abstract The present study explores the structural, optoelectronic, and thermoelectric properties of potassium tin halide vacancy-ordered double perovskites K2SnX6 (X = Cl, Br, and I) in their stable monoclinic phase. Our study uses first-principles calculations based on density functional theory (DFT). Electronic band structures reveal direct band gaps for K2SnCl6 and K2SnBr6, while K2SnI6 exhibits an indirect band gap. Theoretical computations utilising the modified Becke-Johnson potential (mBJ-GGA) demonstrate that the optical band gaps of K2SnCl6, K2SnBr6, and K2SnI6 decrease in the following order: 2.581 eV, 1.707 eV, and 4.126 eV, respectively. These values render the materials suitable for photovoltaic applications. Analysis of dielectric functions, absorption coefficients, and refractive indices demonstrates their potential as light-absorbing materials. We evaluate the thermoelectric properties, including electronic and lattice thermal conductivities, Seebeck coefficients, and power factors, which lead to favorable thermoelectric performance. The maximum figure of merit (ZT) values of 0.58, 0.69, and 0.50 are achieved for K2SnCl6, K2SnBr6, and K2SnI6, respectively, at 500 K. These findings highlight the potential of these materials for applications in solar cells and thermoelectric devices, emphasising their effectiveness at elevated temperatures.

Adjusting Electronic Properties of Janus SHfAZ2 (A═Si,Ge; Z═N, P, As) via Strain Engineering and an Electric Field

AbstractIn this work, novel monolayers of 2D Janus SHfAZ2 (A═Si, Ge; Z═N, P, As) materials are introduced. These Janus structures are primarily investigated for their ability to exhibit adjustable electronic properties when subjected to biaxial strain and an applied electric field. At equilibrium, the four structures in the Janus SHfAZ2 monolayers all display indirect bandgap semiconductor properties, with the exception of the SHfGeN2 monolayer, which exhibits direct bandgap semiconductor properties. Under the influence of biaxial strain, the study observes that the electronic properties of all SHfAZ2 monolayers can be adjusted, transitioning from semiconductor to metallic properties when subjected to compressive strain. However, the SHfSiP2, SHfGeP2, and SHfGeAs2 monolayers show limited sensitivity to an applied electric field, with their electronic properties being modifiable solely under the influence of applied biaxial strain. In contrast, both the SHfSiAs2 and SHfGeN2 monolayers demonstrate the ability to modulate their electronic properties from semiconductors to metals when subjected to both biaxial strain and an applied electric field. Finally, the carrier mobility of these five structures is calculated. The outcomes of the research provide a solid theoretical foundation for the potential utilization of 2D Janus SHfAZ2 monolayers in electronic devices.

Thermoelectric properties of two‐dimensional ternary transition metal nitrides HfNF

AbstractThe exceptional electron transfer properties and low thermal conductivity of two‐dimensional layered materials render them a promising choice for thermoelectric applications. In this study, we explore the stability, electronic properties, and thermoelectric characteristics of materials composed of two‐dimensionally layered transition metal nitride HfNF. Our research findings show that the structure of HfNF is stable and exhibits the properties of a direct bandgap semiconductor. Furthermore, we employ the Boltzmann transport theory and Slack model to investigate the thermoelectric properties of HfNF within the temperature range of 300 to 900 K. The HfNF materials exhibit relatively large thermoelectric dominance values ( values), with the ‐type HfNF demonstrating a maximum value of 1.46. Furthermore, utilizing the quasi‐harmonic Debye model, thermodynamic properties such as heat capacity, coefficient of thermal expansion, and bulk modulus within the 6 GPa and 600 K range are estimated. Based on these calculations, it is predicted that two‐dimensional HfNF materials will serve as promising new materials for thermoelectric applications spanning from 300 to 900 K.

Direct bandgap emission from strain-doped germanium

Germanium (Ge) is an attractive material for Silicon (Si) compatible optoelectronics, but the nature of its indirect bandgap renders it an inefficient light emitter. Drawing inspiration from the significant expansion of Ge volume upon lithiation as a Lithium (Li) ion battery anode, here, we propose incorporating Li atoms into the Ge to cause lattice expansion to achieve the desired tensile strain for a transition from an indirect to a direct bandgap. Our first-principles calculations show that a minimal amount of 3 at.% Li can convert Ge from an indirect to a direct bandgap to possess a dipole transition matrix element comparable to that of typical direct bandgap semiconductors. To enhance compatibility with Si Complementary-Metal-Oxide-Semiconductors (CMOS) technology, we additionally suggest implanting noble gas atoms instead of Li atoms. We also demonstrate the tunability of the direct-bandgap emission wavelength through the manipulation of dopant concentration, enabling coverage of the mid-infrared to far-infrared spectrum. This Ge-based light-emitting approach presents exciting prospects for surpassing the physical limitations of Si technology in the field of photonics and calls for experimental proof-of-concept studies.

Janus Zn3CdC2 and ZnCd3C2 monolayers in carbides: A first-principles study

In this work, two Janus carbides, Zn3CdC2 and ZnCd3C2 monolayers, are designed. The stability, electronic, mechanical, piezoelectric, and light absorption properties are investigated using the first-principles calculations. The results demonstrate that both structures are chemically, dynamically, and thermodynamically stable. A direct bandgap semiconductor, the ZnCd3C2 monolayer has a bandgap of 1.82 eV, while the indirect bandgap semiconductor Zn3CdC2 monolayer has a slightly larger gap of 2.03 eV. However, Zn3CdC2 monolayer can be transformed into a direct bandgap semiconductor by applying biaxial compression at 2%. The mechanical properties indicate that both materials possess significant mechanical anisotropy, high flexibility, and distinctive deformation pattern. More strikingly, two Janus monolayers display out-of-plane piezoelectric properties due to their noninversion symmetry and out-of-plane asymmetry structures. At the same time, the different charge transfer amounts along the x and y directions give them unequal out-of-plane piezoelectric coefficients d31 and d32. For Zn3CdC2 monolayer, the value of d31 is −0.52 pm/V, and the value of d32 is 0.25 pm/V; The values of d31 and d32 for ZnCd3C2 monolayer reach −0.32 pm/V and 0.27 pm/V, respectively. In addition, Zn3CdC2 and ZnCd3C2 monolayers have strong light absorption coefficients as high as 105 cm−1 in visible and ultraviolet bands. Our works reveal that the two Janus monolayers have great potential in piezoelectric, photovoltaic, and other sustainable energy applications.

First-principles study of the effect of doping on the optoelectronic properties of defective monolayers of MoSe2.

In this paper, the structural stability, electronic structure, and optical properties of monolayer MoSe2 doped with C, O, Si, S, and Te atoms, respectively, under defective conditions are investigated based on first principles. It is found that the system is more structurally stable when defecting a single Se atom as compared to defecting a single Mo or two Se atoms. The electronic structure analysis of the system reveals that intrinsic MoSe2 is a direct bandgap semiconductor. The bandgap value of the system decreases with a single Se atom defect and introduces two new impurity energy levels in the conduction band. The defective systems doped with C and Si atoms all exhibit P-type doping. The total density of states of intrinsic MoSe2 is mainly contributed by the Mo-d and Se-p orbitals, and new density of state peaks appears near the conduction band after the defects of Se atoms. The total density of states of the defective system doped by each atom is mainly contributed by Mo-d, Se-p, and the result of the p orbital contribution of each dopant atom. By analyzing the dielectric function of each system, it is found that the intrinsic MoSe2 has the lowest static permittivity and the C-doped defect system has the highest static permittivity, which reaches 21.42. The C- and Si-doped defect systems are the first to start absorbing the light, and the intrinsic MoSe2 absorbs the light later, with its absorption edge starting at 1.25eV. In the visible range, the reflection peaks of the systems move toward the high-energy region and the blue-shift phenomenon occurs. It is hoped that applying modification means to modulate the physical properties of the two-dimensional materials will provide some theoretical basis for broadening the application of monolayer MoSe2 in the field of optoelectronic devices. This study utilizes the first principle computational software package MS8.0 (Materials studio8.0) under density functional theory (DFT). The exchange-correlation potential (GGA-PBE) is described by the Perdew-Burke-Ernzerhof correlation function in CASTEP, and the potential function adopts the ultrasoft pseudopotential in the inverse space formulation. The plane wave truncation energy Ecut is set to 400eV, the K-point is taken as 5 × 5 × 1, and the force convergence criterion is 0.05eV/Å. The convergence accuracy of the total energy of the system is less than 1.0 × 10-5eV/atom, the tolerance shift is less than 0.002Å, and the stress deviation is less than 0.1 GPa. The vacuum layer is taken as 15Å, which is intended to minimize the interlayer force. The vacuum layer was set to 15Å to avoid the effect of layer-to-layer interaction forces in the crystal cell.

First-principles study of the electronic and optical properties of Nb-doped MoSe2 by tensile strain

A first-principles method was used to explore the influence of tensile strain on the electrical and optical characteristics of Nb-doped MoSe2. The tensile strain has been discovered to have a higher influence on the electrical structure of the Nb-doped MoSe2 system than pure monolayer MoSe2. According to the energy band structure study, the pure monolayer MoSe2 is a direct bandgap semiconductor, but the system doped with Nb instead of Mo atoms is a p-type-doped semiconductor. The bandgap of the Nb-doped MoSe2 system decreases gradually with the increase of tensile strain, but still maintains the p-type semiconductor properties, and the bandgap of the pure monolayer MoSe2 also decreases gradually with the increase of tensile strain. From the density of states analysis, it is found that for the total density of states of the doped system at different tensile strains, it is mainly contributed by the Mo-4d and Se-4p orbitals. The optical properties analysis showed that the doped system under tensile strain had higher absorption coefficient and reflectance peak than the Nb-doped MoSe2 system without tensile strain. Additionally, the doped system showed redshift phenomenon in both the absorption and reflection peaks as the tensile strain increased.

A novel large-cell boron nitride polymorph

Through density functional theory simulations, the structural properties, stability, mechanical properties, elastic anisotropy as well as electronic properties for boron nitride allotropes with cubic structure, Pn-3n BN, are investigated in this work. Studying the phonon spectra, molecular dynamics as well as elastic constants of Pn-3n BN, it is found that porous Pn-3n BN is stable in dynamics, thermodynamics and mechanics. The B (bulk modulus), G (shear modulus) and E (Young's modulus) of Pn-3n BN are 64 GPa, 26 GPa and 69 GPa, respectively. The B/G (the ratio of bulk modulus to shear modulus) and v (Poisson's ratio) of Pn-3n BN are 2.43 and 0.319, respectively, which exhibit ductility. The three-dimensional surface construction for Young's modulus, the maximum and minimum of shear modulus, the maximum and minimum of Poisson's ratio of Pn-3n BN are all irregular spheres, indicating that Pn-3n BN has elastic anisotropy. The Emax/Emin of Pn-3n BN displays isotropy with 1.00 in (111) plane, and is not equal to 1.00 in other principal planes, showing anisotropy. The conduction band minimum (CBM) and the valence band maximum (VBM) of Pn-3n BN are both located at point G, and the band gap width of Pn-3n BN is 5.197 eV, from which Pn-3n BN is a wide band gap and direct band gap semiconductor material.

Structure and electrical properties of double-walled silicon nanotubes depending on 585 defects and applied electric fields by SCC-DFTB method

The geometric structural and electronic properties of 585 defective double-walled silicon nanotubes (DWSiNTs) by using the self-consistent charge density functional tight-binding (SCC-DFTB) method. Furthermore, we investigated the impact of external electric field and intensity on the electronic properties. After the relaxation of perfect tubes, the structure of the tube changes significantly, and the winding direction of the tube wall changes. The buckling value of the tube wall is most closely related to the geometric shape and atomic arrangement order of tubes. The overall stability of zigzag tubes is higher than armchair tubes, and (6,6)@(10,10) stability is significantly affected by defects. The partially defected zigzag tubes change from direct band gap semiconductor properties to indirect band gap semi-metal properties. A transformation of the semiconductor-semimetal properties, direct-indirect band gap of DWSiNTs is realized. The charge transfer amplitude of the defect tubes is greater than the perfect tube. The applied electric field makes the stability of all tubes decrease linearly, and the stability of the defect tubes is higher than the perfect tube. Part of the electric field strength changes the defect tubes from semiconductor properties to semi-metal properties, and semi-metal properties to metal properties. These theoretical studies provide a reference for the preparation and future application of DWSiNTs.

Strain-tunable electronic anisotropy of the AlSb double-layer honeycomb structure.

Two-dimensional (2D) materials show promising applications in nanoelectronic devices due to their excellent physical and chemical properties, large specific surface area, and good flexibility. 2D AlSb, a representative of a new class of two-dimensional materials with a double-layer honeycomb (DLHC) structure was recently obtained in experiments and was reported to be a direct band gap semiconductor. Strain engineering is an effective way of tuning the properties of 2D materials. Here, by first-principles calculations, the strain effects on the electronic structure of AlSb were investigated. An interesting inversion of band order near the bottom of the conduction band can be induced by applying uniaxial strain, which will introduce a large electronic anisotropy. In addition, under tensile strain along the armchair direction larger than 5%, band inversion occurs, indicating possible topological insulator properties of AlSb. Small carrier effective mass and strain tunable electronic anisotropy pave the way for the application of AlSb in future nanoelectronic devices.

Twist angle and electric gating controllable electronic structure of the two-dimensional stacked BP homo-structure.

The boron phosphide (BP) van der Waals (vdW) homostructure is designed to construct high-performance nano-optoelectronic devices due to its distinctive photoelectric properties. Using density functional theory, the electronic properties of twisted and untwisted BP bilayer structures are systematically calculated. We found that the 0° structure is a direct band gap semiconductor with a type II band alignment, the carrier mobility of which is increased to 104, and its photoelectric conversion efficiency is 17.3%. By analyzing the band structure and exciton binding energy calculated at 0° under an electric field, it is further found that 0° is a superior photoelectric material. As for the twist BP bilayer, the band gap changes with torsional structures under the applied electric field, which generates the Stark effect. The twist angles of bilayer BP, specifically 13.17°, 21.79°, 38.21°, and 46.83°, always maintain a direct band gap under the influence of an electric field. While 60° is an indirect band gap, the structure exhibits high resistance to the electric field. Our results reveal that bilayer BP is a potential application prospect in photovoltaic and optoelectronic fields and can provide more insights into optoelectronic devices.

A novel investigation of pressure-induced semiconducting to metallic transition of lead free novel Ba3SbI3 perovskite with exceptional optoelectronic properties.

The structural, electronic, mechanical, and optical characteristics of barium-based halide perovskite Ba3SbI3 under the influence of pressures ranging from 0 to 10 GPa have been analyzed using first-principles calculations for the first time. The new perovskite Ba3SbI3 material was shown to be a direct band gap semiconductor at 0 GPa, but the band gap diminished when the applied pressure increased from 0 to 10 GPa. So the Ba3SbI3 material undergoes a transition from semiconductor to metallic due to high pressure at 10 GPa. The Ba3SbI3 material also exhibits an increase in optical absorption and conductivity with applied pressure due to the change in band gap, which is more suitable for solar absorbers, surgical instruments, and optoelectronic devices. The charge density maps confirm the presence of both ionic and covalent bonding characteristics. Exploration into the mechanical characteristics indicates that the Ba3SbI3 perovskite is mechanically stable. Additionally, the Ba3SbI3 compound becomes strongly anisotropic at high pressure. The insightful results of our simulations will all be helpful for the experimental structure of a new effective Ba3SbI3-based inorganic perovskite solar cell in the near future.