Indirect Band Gap Semiconductor Research Articles

Insight on thermodynamic and thermoelectric properties of Ge based perovskites AGeO3 (A = Mg, Cd) for energy harvesting applications: A DFT approach

In this manuscript, transport properties like thermoelectric and thermodynamic properties of AGeO3 (A = Mg, Cd) perovskites have been performed in detail along with effect of chemical potential on various thermoelectric parameters. Furthermore, we present the electronic effects and thermodynamic stability of these materials. The MgGeO3 and CdGeO3 alloys have a gap of 3.368 and 2.555 eV, respectively, making them indirect band gap semiconductors. Furthermore, using a constant relaxation time approximation and semiclassical Boltzmann theory, the thermoelectric (TE) properties of both materials have been studied. The lattice thermal conductivity magnitudes for MGeO3 and CdGeO3 are 7.47 W/mK and 21.55 W/mK, respectively, at 300 K. Power Factor (PF) has been measured at approximately 0 chemical potential, or approximately 14 (1011 W/K2 ms) at 1200 K, 7.5 (1011 W/K2 ms) at 700 K, and 3.5 (1011 W/K2 ms) at 300 K for both MgGeO3 and CdGeO3. At room temperature, the electrical conductivities of MgGeO3 and CdGeO3 were measured to be 1.43 × 1015W/mK and 1.08 × 1015W/mK, respectively. Over a broad temperature range (0–1200 K), the thermodynamic parameters, such as heat capacity, entropy, thermal expansion, and Debye temperature, were also computed and discussed.

The structural, electronic, optical and photocatalytic properties of two-dimensional ZrIN monolayer: A first-principles study

This study presents a comprehensive investigation of the structural stability, electronic and optical properties of two-dimensional ZrIN using first-principles calculations. The stability of 2D ZrIN was confirmed through investigation of thermodynamic, mechanical, dynamic and thermal criteria. The 2D ZrIN is predicted to be an indirect bandgap semiconductor with a gap value of 2.28 eV. It demonstrates high transmittance in the violet segment of the visible spectrum. The photocatalytic properties of 2D ZrIN were also investigated under pH values of 0 and 7 by examining the band edge positions. Additionally, the impact of strain on the band structure and photocatalytic activity. It was found that compressive strain limits the photocatalytic working range of ZrIN monolayer, whereas tensile strain expands working range; however, a further increase in tensile strain leads to decrease in the effective catalytic working region. These findings provide valuable insights into the potential applications of 2D ZrIN in both optoelectronics and catalysis.

DFT study of electron energy loss spectra of sulfur in Janus MoSSe, MoSTe, WSSe and WSTe monolayers

In this paper, electronic properties of Janus MSX monolayers (M = Mo, W; X = Se or Te), including electron energy loss near edge structures (ELNES), as K and [Formula: see text] edge spectra of sulfur atoms, have been calculated using a full potential scheme and the augmented plane wave plus local orbitals (APW+lo) method in the framework of density functional theory (DFT). Due to the lack of experimental results, the obtained spectra are compared with the corresponding spectra of MoS2 monolayer. The band structure analysis shows that the Janus MoSSe and WSSe monolayers are direct bandgap semiconductors, while the Janus MoSTe and WSTe monolayers are indirect bandgap semiconductors. In comparison to MoS2, the main structures of the K edge ELNES spectra of sulfur atoms in Janus monolayers occur at lower energies, due to the structural change and increased bond length. The relative reduction of intensities in the main structures predicts the possibility of reducing the number of partial densities of states (PDOS), that is, the reduced p PDOS for the K edge in the corresponding energy range. In the K ([Formula: see text] edge ELNES spectra of the sulfur atom in Janus monolayers and MoS2 monolayers, the main structures are due to the electron transfer to the unoccupied [Formula: see text] and [Formula: see text] states (3s of sulfur and 4d states of the transition metal).

Comprehensive analysis of structural, mechanical, optoelectronic, and thermodynamic properties of Ba2XBiO6 (X = Y, La) double perovskites using density functional theory

The structural, mechanical, optoelectronic, and thermodynamic properties of Ba2XBiO6 (X = Y, La) double perovskites are critically analyzed using density functional theory. The Birch-Murnaghan equation of state confirms their structural stability, supported by tolerance factor analysis. For Ba2YBiO6 and Ba2LaBiO6, negative formation energies are −0.935 eV for Ba2YBiO6 and −0.836 eV for Ba2LaBiO6, confirming thermodynamic stability. Phonon dispersion curves indicate stable lattice vibrations, reducing the likelihood of spontaneous structural changes or phase transitions. Ba2YBiO6 possesses higher elastic constants C 11 = 222 GPa shows stiffness and exhibits brittle mechanical behavior, whereas the Pugh ratio and C 11 = 217 GPa for Ba2LaBiO6 shows ductility. The Poisson ratio classifies Ba2YBiO6 as a non-central force crystal and Ba2LaBiO6 as a central force crystal. Both materials are indirect band gap semiconductors, with band gap values of 0.75 eV for Ba2YBiO6 and 2.05 eV for Ba2LaBiO6. Optical properties suggest applications in UV and visible light-based optoelectronic devices. Thermodynamic properties, such as Debye temperature and heat capacity, support the idea that these materials are suitable for high mechanical applications. These findings provide insights for designing high-performance optoelectronic and mechanical devices.

Optical response of Zr[formula omitted]CO[formula omitted]/MoS[formula omitted] van der Waals heterostructures calculated using first-principles calculations

In the field of material science, the search for a material with an optimal bandgap of approximately 1.40 eV that can act as an efficient photocatalyst for water splitting using solar spectrum irradiation is a noble mission. In this article, we explore the structural, electronic structure, optical and photocatalytic properties of Zr2CO2/MoS2 vdW heterostructures. Our results demonstrates that the Zr2CO2/MoS2 vdW heterostructure can be reliably synthesized. This is due to a minimal lattice mismatch of less than 3%, a negative adhesion energy of -4.23 meV/Å 2, and inherent dynamic stability. The electronic band structure calculations indicate that the Zr2CO2/MoS2 vdW heterostructure is an indirect bandgap semiconductor. We found that the conduction band minimum (CBM) and valance band maximum (VBM) of the heterostructure are located in different monolayers. Furthermore, under −2% biaxial strain a transition from type-I to type-II (staggered) band alignment occurred. Stacking 2D MoS2 on the Zr2CO2 monolayer results in a vdW heterostructure, and as a result, the HSE calculated bandgap of the Zr2CO2/MoS2 vdW heterostructure in most stable configuration lying in the ideal range for photocatalytic applications. We also studied the heterostructure’s optical properties to understand its response to incident photons with energies up to 14 eV. Based on our findings, Zr2CO2/MoS2 heterostructures are desirable for optoelectronic device applications operated in visible range. Our research offers fresh recommendations for developing novel, highly effective photocatalytic compounds with numerous optical device applications.

First-principles study of the structural, electronic, magnetic and elastic properties of YxGd1-xN alloys

ABSTRACT The structural stability, electronic structure, and optical properties of the novel Y x Gd1-x N ternary alloys were studied using the FP-LAPW method with the generalized gradient approximation + Hubbard U (GGA + U). Our results reveal that YxGd1-xN alloys can be experimentally synthesized because they exhibit energetic and mechanical stability. All these systems present semiconducting behavior. Both GdN and YN are indirect band gap semiconductors while YxGd1-xN alloys are direct band gap semiconductors for x = 0.25 , 0.5 , 0.75 because of hybridization between d (Y) and Gd(f) orbitals in the vicinity of the Fermi energy level. The f-d coupling induces the major magnetic moments on the Gd atom. The absorption spectra are reasonably high (>105 cm−1) and the bandgap energy and structure spacing match between YN and GaN which made Y x Gd1-x N alloys suitable for optoelectronic applications. In the absence of experimental work, our results can be useful for further studies.

Epitaxial Group-IV Quantum Dots as Room-Temperature Light Emitters

Next-generation Si-based applications ranging from short-range (quantum) data transfer to sensing could highly benefit from potential progress in group-IV-based telecom light emitters that can be readily implemented with Si Photonics components [1]. However, since Si is known to be an indirect band gap semiconductor, light emission is limited and inhibits the integration of efficient emitters, such as, e.g. light-emitting diodes and lasers on Si Photonic platforms.In this presentation, we stress that a particular type of epitaxial Ge on Si quantum dots allows for overcoming the indirect bandgap limitations of Si and Ge and, thus, enables pronounced light emission even at room temperature and above [2]. These nanostructures consist of ~2 nm high Ge-rich quantum dots on Si(001) substrate epitaxially created via strain-driven formation. However, in contrast to commonly used nanostructures, we intentionally incorporate point defects into these nanostructures during their growth through in-situ low-energy Ge ion implantation [3-4]. Therefore, the point defects can be confined within the 2 nm thick Ge layer while the surrounding Si matrix remains perfectly crystalline. We will discuss the superior light-emission properties of these so-called defect-enhanced quantum dots (DEQDs) and present the current theoretical understanding of the defect’s effects on the band structure. The latter leads to the enhanced light emission from DEQDs and the opening of direct recombination channels in k-space [5,6].In addition to signs for optically pumped lasing from DEQDs embedded in microdisk resonators, implementing these emitters into the i-region of p-i-n diodes is remarkably straightforward since the matrix material is crystalline Si [7,8]. To showcase the superior properties of these zero-dimensional light emitters, we highlight light emission from DEQD light-emitting diodes with exceptional temperature stability up to 100°C [9]. This behavior starkly contrasts conventional Si/Ge light emitters, for which the light emission is typically confined to cryogenic temperatures.For optimizing the light emission from this interlaced defect/nanostructure complex [10], we elaborate on the testing of crucial parameters related to the temperature stability of the DEQDs [8,11], the scalability of light emission with increasing the density of the DEQDs [12] and passivation of detrimental defects in the Si matrix [13].[1] I. A. Fischer, et al., APL Photonics 7, 050901 (2022).[2 ] M. Brehm, Silicon Photonics IV, 67-103, Silicon Photonics IV: Innovative Frontiers, edited by David J. Lockwood and Lorenzo Pavesi, Springer series Topics in Applied Physics (2021).[3] M. Grydlik, et al., Nano Lett. 16, 6802–6807 (2016).[4] M. Grydlik, et al., ACS Photonics 3, 298–303 (2016).[5] F. Murphy-Armando, et al., Physical Review B 103 (8), 085310 (2021).[6] M. Brehm, et al., to be published[7] H. Groiss et al., Semicond. Sci. Technol. 32, 02LT01 (2017).[8] L. Spindlberger et al., Crystals 10, 351 (2020).[9] P. Rauter et al., ACS Photonics 5, 431-438 (2018).[10] M. Brehm and M. Grydlik, Nanotechnology 28, 392001 (2017).[11] L. Spindlberger et al., Physica Status Solidi (a) 216, 1900307 (2019).[12] H. Groiss et al., Semicond. Sci. Technol. 32, 02LT01 (2017).[13] L. Spindlberger et al., Appl. Phys. Lett. 118, 083104 (2021).

Engineering the electronic properties of MoTe2 via defect control

ABSTRACT The remarkable electronic properties of monolayer MoTe2 make it a very adaptable material for use in optoelectronic and nano electronic applications. MoTe2 growth often exhibits intrinsic defects, which significantly influence the material’s characteristics. In this work, we conducted a thorough investigation of the electronic characteristics of intrinsic defects, including point defects, in monolayer MoTe2 using first-principles calculations based on density functional theory (DFT). Our findings indicate that the presence of point defects leads to the formation of n-type properties as the Fermi level situates above the conduction band. Our first-principal density functional theory calculation revealed an appearance of donor level in the band gap close to the conduction band in MoTe2. Our study signifies that the formation energy of a vacancy in a Te atom is lower than that of both a vacancy in a Mo atom and two vacancies in Te atom. This suggests that during the synthesis process, it is more probable for Te atom vacancies to be created. A defect in the pristine monolayer of MoTe2 leads to a slight decrease in the band gap, causing a transition from a direct band gap semiconductor to an indirect band gap semiconductor. The results of our study indicate that the presence of vacancy defects may modify the electronic properties of monolayer MoTe2, suggesting its potential as a new platform for electronic applications. Hence, our analysis offers significant theoretical backing for defect engineering in MoTe2 monolayers and other 2D materials, a critical aspect in the advancement of nanoscale devices with the desired functionality.

Exploring tunable optoelectronic properties of two-dimensional GaS/PtSSe heterostructures under biaxial strain and external electric field

Vertically stacked heterostructures offer novel material options for designing tunable optoelectronic devices due to their adjustable electronic and optical properties. This work compares the electronic structure, charge transfer, and optical properties of two different contact faces of GaS/Janus PtSSe heterostructures using the density functional theory. The results show that GaS/PtSSe form a built-in electric field at the interface, directing from the monolayer GaS to the PtSSe. GaS/SePtS and GaS/SPtSe are determined to be indirect bandgap semiconductors with bandwidths of 1.51 eV and 1.11 eV utilizing the PBE. In this study, the band alignment of GaS/PtSSe can induce a semiconductor-to-metal transition. Notably, GaS/SePtS is highly sensitive to biaxial strain and external electric field, transitioning its energy band alignment from Type-I to Type-II. Applying tensile strain enhances the sunlight absorption of GaS/PtSSe, making it a promising candidatein the tunable electronic devices and photodetectors.

Prediction of a rippled and auxetic two-dimensional Sn9C15 layers with tunable electronic band structure: A first-principle study

We predicted a two-dimensional Sn9C15 monolayer with regular ripple using first-principles methods by utilizing the VASP code based on density functional theory (DFT). The rippled Sn9C15 monolayer is an indirect bandgap semiconductor with anisotropic mechanical properties (Poisson’s ratio and Young’s modulus). It exhibits auxetic properties with a negative Poisson’s ratio (NPR) of up to −0.58 and exceptional flexibility in the x direction. Furthermore, its bandgap can be adjusted from 1.16 eV to 0.68 eV with a strain in the x direction of less than 12 %. The rippled Sn9C15 monolayer is sensitive to polarized light and has a broad absorption spectrum from infrared to ultraviolet. In addition, the bilayer rippled Sn9C15 exhibits a regularly arranged nanotube-like structure and is a stable direct bandgap semiconductor material. These findings enrich the emerging landscape of 2D rippled monolayers and suggest potential applications in diverse fields such as optics, nanomechanics, electronic devices, and filtration.

Effect of different contact interfaces on electronic and optical properties in the heterojunction of SiC2/MoSSe

We investigate the effect of different contact interfaces on the electronic and optical characteristics of the SiC2/MoSSe heterojunction. It is found that SiC2/MoSSe(S) heterojunction is an indirect band gap semiconductor with type II band alignment. The SiC2/MoSSe (Se) heterojunction is a direct band gap semiconductor with a type Ⅰ band alignment. The difference in electronic properties between the two heterostructures comes from the different orientations of the intrinsic electric field of Janus MoSSe in the heterojunction. The band gap and energy band alignment are modulated under the applied electric field. Moreover, the optical properties of SiC2/MoSSe (Se) are better than the SiC2/MoSSe(S), and the applied electric field can improve the optical properties of the heterojunction. The results provide a potential way for efficient photovoltaic materials.

Geometrical, elastic, electronic, phonon, and optical properties of Na3AgO2 from first-principles calculation

In this paper, the geometrical, elastic, electronic, phonon, and optical properties of Na3AgO2 have been systematically studied by first-principles calculation. The results show that Na3AgO2 is mechanically stable and has small compressibility. Na3AgO2 is an indirect band-gap semiconductor with weak interatomic interaction. The bandgap calculated by HSE06 is 2.314 eV, and that calculated by GGA is 1.261 eV. For Na3AgO2, in the valence band near the Fermi level, the curve peaks of TDOS at −2.11 eV and −0.885 eV are primarily composed of O 2p states, which hybridize the 4 d and 4p states of Ag. The conduction band mainly consists of the 4p, 4 d, and 5s states of Ag, while hybridizing a few 2p states of O and a few 2p and 3s states of Na. As can be seen from the phonon dispersion spectrum there is no negative phonon frequency in the whole Brillouin region, indicating the structure is stable. Mulliken bond population of Na3AgO2 shows that O–Ag bonds have strong covalency, O–Na bonds have strong ionic properties, Na–Na bonds and Na–Ag bonds are antibonding. Na3AgO2 has a small reflectivity and a small absorption coefficient in the direction of (100) and (010) and has good transparency. The transparency of blue-violet light in the (001) direction is not as good as that of low-energy visible light. The obtained results lead to the conclusion that Na3AgO2 is a promising p-type transparent conducting material and is expected to be applied in practice.

Physical properties of novel double perovskite oxides Ba2XSbO6(X = P, As) by first-principle calculations

In this article, the structural, mechanical, electronic, optical, thermal, and thermodynamic properties of Ba2XSbO6 (X=P, As) double perovskite oxides were investigated by using first-principles calculations. The results show that the Goldsmith’s tolerance factor and octahedral factor of the two perovskites are in a stable range, the binding energy and formation energy are negative, and the elastic constants meet the Born-Huang stability criterion. These results suggest the stability of the two perovskite oxides. The mechanical property study indicates that Ba2XSbO6 (X=P, As) exhibits high bulk modulus and shear modulus. Poisson’s ratio (ν) and the elastic anisotropy index (A) suggest that they are anisotropic ductile materials. The electronic properties show that Ba2PSbO6 and Ba2AsSbO6 are indirect bandgap semiconductors with bandgap values of 2.130 eV and 1.596 eV, respectively. The optical properties show that Ba2XSbO6 (X=P, As) has excellent light absorption capacity in the range of 2.5–30 eV. Specifically, Ba2AsSbO6 has a higher absorption capacity for visible light compared to Ba2PSbO6. Thermodynamic properties show that the Debye temperature of the two perovskites is higher than 420 K, the melting points is higher than 1700 K, the minimum lattice thermal conductivities is close to 1, and the specific heat reaches the Dulong-Petit limit at about 700 K. This study shows that the double perovskite oxide Ba2XSbO6 (X=P, As) has important potential in the field of thermoelectricity and optoelectronics.

Effect of biaxial strain on the electronic structure and optical properties of two-dimensional Bi2Te2S

In this work, the effects of biaxial strain on the electronic structure and optical properties of monolayer Bi2Te2S are studied by the first-principles methods. The calculated results show that the monolayer Bi2Te2S is an indirect band gap semiconductor with a band gap of 1.0 eV. The absence of imaginary frequency in the phonon spectrum indicates that the structure can exist stably. With the increase of tensile strain, the band gap value decreases approximately quasi-linearly. When 10 % tensile strain is applied, the band gap value is reduced to 0 eV, achieving the transition from an indirect bandgap semiconductor to a direct bandgap semiconductor. With the increase of compressive strain, the band gap value increases first and then decreases, and the band gap value reaches a maximum of 1.28 eV at −4 % strain. Combined with the density of states analysis, the reason for this change in the band structure is that the contribution of Bi 6p, Te 5p and S 3p state electrons to the conduction band and valence band changes under different strains. The effect of strain on the optical properties shows that when different strains are applied, the monolayer Bi2Te2S has a high absorption coefficient in the entire visible region. The single-layer Bi2Te2S material has a smaller refractive index under tensile strain. The static dielectric function value increases with the increase of tensile strain, and the peak value of the dielectric function decreases and moves to the low energy direction. This indicates that the tensile strain will enhance the migration of photogenerated electron-hole pairs, which is beneficial to improving the utilization of light. This work will provide a theoretical reference for the subsequent study of the electronic and optical properties of monolayer Bi2Te2S.

A first-principles prediction of novel Janus ZrGeZ3H (Z = N, P, and As) monolayers: Raman active modes, piezoelectric responses, electronic properties, and carrier mobility.

In this article, an attempt is made to explore new materials for applications in piezoelectric and electronic devices. Based on density functional theory calculation, we construct three Janus ZrGeZ3H (Z = N, P, and As) monolayers and study their stability, piezoelectricity, Raman response, and carrier mobility. The results from phonon dispersion spectra, ab initio molecular dynamics simulation, and elastic coefficients confirm the structural, thermal, and mechanical stability of these proposed structures. The ZrGeZ3H monolayers are indirect band gap semiconductors with favourable band gap energy of 1.15 and 1.00 eV for the ZrGeP3H and ZrGeAs3H, respectively, from Heyd-Scuseria-Ernzerhof functional method. It is found that the Janus ZrGeZ3H monolayers possess both in-plane and out-of-plane piezoelectric coefficients, revealing that they are potential piezoelectric candidates. In addition, the carrier mobilities of electrons and holes along transport directions are anisotropic. Notably, the ZrGeP3H and ZrGeAs3H monolayers have high electron mobility of 3639.20 and 3408.37 cm2 V-1 s-1, respectively. Our findings suggest the potential application of the Janus ZrGeZ3H monolayers in the piezoelectric and electronic fields.

Unveiling the electronic, optical, thermoelectric, and magnetic properties of novel Ba2GdMO6 (M = Pa, Ta) via DFT calculation

The optoelectronic, thermoelectric, and magnetic properties of novel Ba2GdMO6 (M = Pa, Ta) double perovskites have been computed with the spin-polarized density functional investigation. The calculations are performed using the FP-LAPW method in Wein2K code, by employing the GGA + U approximations. The band structures and density of states analysis show that Ba2GdPaO6 is an indirect band gap semiconductor with band gap values of 3.0 eV and 3.1 eV in the up and down spin channels, respectively. The Ba2GdTaO6 is also predicted as a semiconducting material with a direct band gap of 2.9 eV and 3.0 eV in up and down spin channels. The optical characteristics of the materials, such as the dielectric constants, absorption coefficient, reflectivity, loss function, and refractive index are computed. The optical results reflect that the materials are excellent choices for high-energy absorbent. The Seebeck coefficient increases beyond the temperature of 300 K for Ba2GdPaO6 and 400 K for Ba2GdTaO6. The increase in the Seebeck coefficient values suggests that these materials are p-type semiconducting. The ferromagnetic nature of the materials has been confirmed by predicting the ferromagnetic phase to be the most stable state. The total magnetic moments of the materials are found equal to 7 µB.

2D Janus TeMoZAZ’ (A = Si,Ge; Z,Z’ = N, P, As; Z ≠ Z'): First‐Principles Insight into the Electronics, and Piezoelectric Properties

AbstractJanus materials possess a diverse array of properties resulting from the breaking of mirror and inversion symmetries, holding significant potential for nanodevices. This study explores the novel TeMoZAZ' (A = Si,Ge; Z,Z' = N, P, As; Z ≠ Z') monolayers derived from the MoA2Z4 monolayer. Utilizing first‐principles calculations, the stability, electronic, transport, mechanical, and piezoelectric properties of the TeMoZAZ' monolayers are investigated. Among the 12 investigated structures, only five‐ TeMoNSiP, TeMoNSiAs, TeMoPSiAs, TeMoAsSiP and TeMoAsGeP monolayers‐ are found to be stable. The electronic properties analysis reveals metallic behavior in the TeMoNSiAs monolayer, while the remaining structures exhibit indirect or direct band gap semiconductor properties. Futher examination of the semiconducting monolayers indentifies the TeMoAsSiP monolayer with notably high hole carrier mobility along the y‐direction, reaching up to 3622.33 cm2 s−1 V−1. Moreover, investigation into the piezoelectric properties of these four semiconductor structures suggests their suitability for diverse applications in piezoelectric devices. Additionally, the effects of biaxial strain on the electronic and piezoelectric properties of these four semiconductor structures are explored. These findings propose a novel approach for designing 2D Janus materials, expanding the repertoire of 2D MA2Z4‐based Janus family and offering promising candidates for optoelectronic devices, wearable devices, and electromechanical systems.

Large valley splitting induced by spin-orbit coupling effects in monolayer Hf3N2O2

Valleytronics is an emerging field of electronics that aims to utilize valley degrees of freedom in materials for information processing and storage. Nowadays, the valley splitting of 2D materials is not particularly large, therefore, the search for large valley splitting materials is very important for the development of valleytronics. This work theoretically predicts that MXene Hf3N2O2 is a 2D material with large valley splitting. It is an indirect bandgap semiconductor with a bandgap of 0.32 eV at the PBE level and increases to 0.55 eV at the HSE06 level. Since Hf3N2O2 breaks the symmetry of spatial inversion, when we consider spin–orbit coupling (SOC), there is a valley splitting at K/K′ of the valence band with a valley splitting value of 98.76 meV. The valley splitting value slightly decreases to 88.96 meV at the HSE06 level. In addition, The phonon spectrum and elastic constants indicate that it is both dynamically and mechanically stable. According to the maximum localization of the Wannier function, it is obtained that the Berry curvature is not zero at K/K′. When a biaxial strain is applied, Hf3N2O2 transitions from metal to semiconductor. With increasing biaxial strain, the valley splitting value increased from 70.13 meV to 109.11 meV. Our research shows that Hf3N2O2 is a promising material for valleytronics.

Comparative Study of the Mechanical, Electronic Structure, and Optical Properties of Cubic Lithium‐Based Perovskite LiMgX3 (X = Cl, Br, I) under Pressure Effects: First‐Principles Calculations

The mechanical, electronic structure, and optical properties of lithium‐based perovskite LiMgX3 (X = Cl, Br, I) are investigated for the first time at 0–20 GPa using density‐functional theory. The Born stability criteria reveal that the phase transition points of LiMgCl3, LiMgBr3, and LiMgI3 are 20.7, 20.9, and 23.4 GPa, respectively. At 0 GPa, studies on the electronic properties using the Heyd‐Scuseria‐Ernzerhof (HSE06) functional show that LiMgCl3 and LiMgBr3 are indirect bandgap insulators with values of 5.336 and 4.113 eV, whereas LiMgI3 is an indirect bandgap semiconductor with a value of 2.055 eV. In addition, the bandgap calculated using both the PBEsol and HSE06 functionals decreases with increasing pressure, and the bandgap trends with pressure are consistent. Both functionals are also used to study the optical properties of LiMgX3 compounds, which show that they have potential for use in vacuum ultraviolet and photovoltaic applications. The mechanical and optical characteristics of the materials are significantly enhanced under pressure.

Physical performances for six novel Si allotropes in hexagonal 15 and 18 stacking orders

Elevating visible light absorption and carrier transport capacity of diamond silicon is a terrifying challenge for improving photoelectric conversion efficiency. Here, six new crystals with similar stacking patterns but various arrangement orders to Si–I are predicated by the random approach combined with group and graph theories. Considering potential applications in the photovoltaic field, we have conducted a detailed study on the stability and physical properties of these structures by first-principles calculations. As a result, these new structures meet mechanical, dynamic, and thermodynamic stabilities, and they are all indirect band gap semiconductor. In particular, among these materials, the effective mass of the smallest hole is only 0.11m0, which is smaller than that of diamond silicon. This result indicates that these structures have better carrier transport capabilities than diamond. In addition, XRD patterns of these six structures were studied for shedding more light for developing these structures in the experiment.