Direct Gap Research Articles

Bandgap Characteristics of Boron-Containing Nitrides—Ab Initio Study for Optoelectronic Applications

Hexagonal boron nitride (h-BN) is recognized as a 2D wide bandgap material with unique properties, such as effective photoluminescence and diverse lattice parameters. Nitride alloys containing h-BN have the potential to revolutionize the electronics and optoelectronics industries. The energy band structures of three boron-containing nitride alloys—BxAl1−xN, BxGa1−xN, and BxIn1−xN—were calculated using standard density functional theory (DFT) with the hybrid Heyd–Scuseria–Ernzerhof (HSE) function to correct lattice parameters and energy gaps. The results for both wurtzite and hexagonal structures reveal several notable characteristics, including a wide range of bandgap values, the presence of both direct and indirect bandgaps, and phase mixing between wurtzite and hexagonal structures. The hexagonal phase in these alloys is observed at very low and very high boron concentrations (x), as well as in specific atomic configurations across the entire composition range. However, cohesive energy calculations show that the hexagonal phase is more stable than the wurtzite phase only when x > 0.5, regardless of atomic arrangement. These findings provide practical guidance for optimizing the epitaxial growth of boron-containing nitride thin films, which could drive future advancements in electronics and optoelectronics applications.

Elevating NIR photonic integration with tantalum-niobium pentoxide

In this study, we present a novel material platform based on tantalum-niobium pentoxide (TaNbO5) for integrated photonics applications. TaNbO5 demonstrates exceptional attributes suitable for both linear and nonlinear optics across a wide range of near-infrared wavelengths. Our analysis of the TaNbO5 unit cell revealed crucial lattice parameters and a direct band gap value of 2.268 eV. At a wavelength of 1550 nm, TaNbO5 exhibits a refractive index of 2.22, an extinction coefficient of 5.24 × 10−4, and other optical properties. We determine a 0.8 μm cut-off core width for single-mode TaNbO5 waveguides, which achieve efficiencies exceeding 99% for single-mode configurations and 98% for multimode structures. When coupled with conventional waveguides, TaNbO5 waveguides demonstrate excellent transmission characteristics. Notably, at a wavelength of 1.55 μm, the single-mode waveguide exhibits minimal excess loss. These findings highlight the significant potential of TaNbO5 waveguides for various near-infrared applications, emphasizing their versatility and promising performance.

Highly Polarization‐Sensitive Solar‐Blind Ultraviolet Photodetection Based on 1D Rb2CuCl3 Microwires

AbstractPolarization‐sensitive solar‐blind ultraviolet (UV) photodetectors are essential in both civilian and military applications. 1D perovskites derivative Rb2CuCl3 holds promise for polarization‐sensitive solar‐blind UV photodetectors due to its wide direct bandgap, anisotropic crystal structure, and long carrier lifetime. However, no studies on the polarization properties of Rb2CuCl3 are reported. Here, the electronic structural anisotropy of Rb2CuCl3 is confirmed by calculating the partial charge density distribution in the ac‐plane and bc‐plane. Then, the Raman‐active modes and corresponding atomic vibration modes are explored within the bc‐plane through joint experimental and theoretical Raman spectroscopy. Besides, angle‐resolved Raman, photoluminescence, and absorption spectroscopy reveal the intriguing anisotropic photoelectric characteristics of Rb2CuCl3 microwires (MWs). By using single Rb2CuCl3 MW as the photoactive layer, a polarization‐sensitive solar‐blind UV photodetector is fabricated, showing high photoresponsivity of 78 mA W−1 and photocurrent anisotropy ratio of ≈1.7 at 265 nm. Importantly, the proposed photodetectors without encapsulation exhibit excellent stability in ambient air, retaining the original photocurrent after two months, showcasing practical applicability. This study underscores the promise of Rb2CuCl3 for high‐performance polarization‐sensitive solar‐blind UV photodetectors, contributing valuable insights into its electronic structure, photoelectric properties, and practical applicability.

Van der Waals ZnO/HfSn2N4 Heterojunction with Exceptional Photoresponse for Photodetectors.

Two-dimensional van der Waals heterojunctions represent a promising avenue for a spectrum of optoelectronic endeavors. Nonetheless, their deployment has been somewhat constrained by the suboptimal efficiency of the photocurrent generated. In this article, a ZnO/HfSn2N4 heterojunction is proposed to achieve high photoresponse efficiency. First-principles calculations are utilized to confirm that this heterojunction possesses thermal stability with a direct bandgap (1.36 eV). It exhibits a high light absorption coefficient and high carrier mobility (2.51 × 103 cm2 V-1 s-1), and biaxial strain has a significant effect on the modulation of the band structure. As the tensile strain increases, the bandgap changes nonlinearly, transitioning from a type-II to a type-I heterojunction. When compressive strain increases, the bandgap decreases. Quantum transport simulations are employed to calculate the density of states and transmission spectrum of the ZnO/HfSn2N4 model, verifying its excellent photoresponse (a photocurrent peak reaching 4.93 a02/photon and an extinction ratio peak of 75.1). It shows that the ZnO/HfSn2N4 heterojunction is a potentially efficient photodetector.

Switchable Photovoltaic Effect and Robust Nonlinear Optical Response in a High-Temperature Molecular Ferroelectric [C8N2H22][PbI4

Hybrid organic-inorganic molecular ferroelectrics (HOIMFs) have garnered significant attention for their potential applications in nonvolatile memory and spintronic devices. However, few efforts have been devoted to the photoelectric properties of lead halide molecular ferroelectrics, despite the fact that robust ferroelectricity and flexibility are desirable for thin-film photoelectric devices. Herein, we present a novel lead halide molecular ferroelectric [C8N2H22][PbI4] (1) synthesized hydrothermally. A polar monoclinic structure of 1 was solved by single-crystal X-ray diffraction and second-harmonic generation (SHG) tests. A direct band gap of 2.36 eV was confirmed by UV-vis spectrum and theoretical calculation. Hysteresis measurements demonstrated inherent room-temperature (RT) ferroelectricity in 1 with a spontaneous polarization (Ps) of 3.2 μC/cm2. The 1-based photoelectric device shows a notable photovoltaic (PV) effect with Voc ∼ 0.27 V, Jsc ∼ 38 nA/cm2 under AM 1.5 G illumination, and a rapid response time of ∼1.5 ms. A considerable enhancement in PV performance has been achieved by adjusting the ferroelectric polarization, resulting in a maximum Voc ∼ 0.75 V, Jsc ∼ 2.28 μA/cm2. Notably, 1 exhibits a rather large SHG signal, which is approximately 2.61-fold higher than that of KH2PO4 (KDP) upon a 1064 nm laser radiation. This study offers a bright avenue for lead halide molecular ferroelectrics as promising optoelectronic devices and SHG materials.

Investigating the Impact of Stress on the Optical Properties of GaN-MX2 (M=Mo, W; X=S, Se) Heterojunctions Using the First Principles

This study used the first-principles-based CASTEP software to calculate the structural, electronic, and optical properties of heterojunctions based on single-layer GaN. GaN-MX2 exhibited minimal lattice mismatches, typically less than 3.5%, thereby ensuring lattice coherence. Notably, GaN-MoSe2 had the lowest binding energy, signifying its superior stability among the variants. When compared to single-layer GaN, which has an indirect band gap, all four heterojunctions displayed a smaller direct band gap. These heterojunctions were classified as type II. GaN-MoS2 and GaN-MoSe2 possessed relatively larger interface potential differences, hinting at stronger built-in electric fields. This resulted in an enhanced electron–hole separation ability. GaN-MoSe2 exhibited the highest value for the real part of the dielectric function. This suggests a superior electronic polarization capability under an electric field, leading to high electron mobility. GaN-MoSe2 possessed the strongest optical absorption capacity. Consequently, GaN-MoSe2 was inferred to possess the strongest photocatalytic capability. The band structure and optical properties of GaN-MoSe2 under applied pressure were further calculated. The findings revealed that stress significantly influenced the band gap width and light absorption capacity of GaN-MoSe2. Specifically, under a pressure of 5 GPa, GaN-MoSe2 demonstrated a significantly narrower band gap and enhanced absorption capacity compared to its intrinsic state. These results imply that the application of stress could potentially boost its photocatalytic performance, making it a promising candidate for various applications.

DFT investigation of thermodynamic, electronic, optical, and mechanical properties of XLiH3 (X= Mg, Ca, Sr, and Ba) hydrides for hydrogen storage and energy harvesting

The present study investigates the hydrogen storage capacity and physical properties of the perovskite hydrides XLiH3 (X = Mg, Ca, Sr, and Ba). The studied compounds MgLiH3, CaLiH3, SrLiH3, and BaLiH3 have lattice constants 3.76, 4.29, 4.64, and 5.04 Å, respectively. These compounds are also observed to be stable in cubic phase under atmospheric pressure and temperature conditions. They have hydrogen storage capacities 8.76 wt%, 5.99 wt%, 3.07 wt%, and 2.03 %, respectively. The SrLiH3 compound has the greatest Debye temperature (θD) of 344.41 K. The analysis of the electronic band structure and density of states reveals that perovskite hydrides have semiconducting characteristics with indirect band gap values of 2.66, 2.34, 1.94, and 1.37 eV, respectively. The materials are semiconductors and have suitable band gaps to be utilized in optical devices. Therefore, the optoelectronic properties of dielectric constants, absorption, and energy loss have been determined to predict the potential of materials for optoelectronic applications. Furthermore, the elastic constants, moduli, and anisotropy are also calculated for the observed materials. The Possion and Pugh ratios indicate these compounds exhibit ductile behaviour and significant anisotropy. Therefore, large values of hydrogen capacities, stabilities, and extraordinary physical behaviour make them important for hydrogen storage systems.

The impact of stress and interface composition on the study of CsF/CsPbX3 inorganic perovskite heterojunctions

In this paper, using first-principles calculations, we have shown that the electronic properties of the CsF/CsPbX3 (X = Cl, Br, I) heterojunctions can be effectively modulated by applying in-plane strain. The CsF/CsPbX3 heterojunction structures exhibit low-lattice mismatch ratios (Cl-Br-I, 3.6 %-1.8 %-4.3 %). Pb²⁺ and F⁻ attract each other to form PbF2, Cs+ and X−attract each other to form CsX. The binding energies are -0.578, -0.406, and -0.723 eV (Cl, Br and I), respectively, indicating that CsF/CsPbI3 exhibits the superior stability. Three heterojunctions are direct band gap semiconductors and the band gaps increase compared to inorganic perovskites (ΔEg:CsPbCl3CsPbBr3CsPbI3, 0.640–0.652–0.601 eV). The partial density of states indicates that the band gap contribution is related the [PbX3]− octahedron and F−. It is evident from the absorption spectra that the interaction of the CsF/CsPbX3 heterojunctions produces a blue shift. By combining multiple layers of CsF and CsPbX3, an overall broad spectral response can be achieved. The optical parameters of CsF/CsPbX3 are consistent with the changes in the band gap. This study demonstrates that CsF can enhance the stability adjust of the spectral response range of inorganic perovskite sensors, and improve the optical absorption performance. The study provides valuable theoretical guidance for the research of high-performance CsF/CsPbX3 heterojunction sensors.

Structure prediction of stable sodium germanides at 0 and 10 GPa

In this paper we used random structure searching (AIRSS) to carry out a systematic search for crystalline Na-Ge materials at both 0 and 10 GPa. The high-throughput structural relaxations were accelerated using a machine-learned interatomic potential (MLIP) fit to density-functional theory (DFT) reference data, allowing ∼1.5 million structures to be relaxed. At ambient conditions we predict three new Zintl phases, Na3Ge2,Na2Ge, and Na9Ge4, to be stable and a number of Ge-rich layered structures to lie in close proximity to the convex hull. The known NaδGe34 clathrate and Na4Ge13 host-guest structures are found to be relatively stabilized at higher temperature by vibrational contributions to the free energy. Overall, the low-energy phases exhibit exceptional structural diversity, with the expected mixture of covalent and ionic bonding confirmed using the electron-localization function (ELF). The local Ge structural motifs present at each composition were determined using smooth overlap of atomic positions (SOAP) descriptors and the Ge-K edge was simulated for representatives of each motif, providing a direct link to experimental x-ray absorption spectroscopy (XAS). Two Ge-rich phases are predicted to be stable at 10 GPa; NaGe3 and NaGe2 have simple kagome and simple hexagonal Ge lattices respectively with Na contained in the pores. NaGe3 is isostructural with the MgB3 and MgSi3 family of kagome superconductors and remains dynamically stable at 0 GPa. Removing the Na from NaGe2 results in the hexagonal lonsdalite Ge allotrope, which has a direct band gap. Published by the American Physical Society 2024

Innovative synthesis and forensic applications of bio-mediated SrO–MgO–In[formula omitted]O[formula omitted] nanocomposites with blue photoluminescence

The first of its kind Strontium oxide–Magnesium Oxide–Indium oxide (SMI) nanocomposites were synthesized utilizing a bio-mediated method with Euphorbiatirucalli latex as a reducing agent, followed by calcination. Synthesis of SMI NCs is confirmed by Bragg reflections of SrO, MgO, and In2O3, among them peaks belonging to In2O3 are observed to be prominent. The crystallite size, and other parameters like dislocation density, strain, structural factor, and crystallinity were estimated. Due to lower surface energy and the adhesion of particles with weak forces, morphology of the surface contains a larger degree of agglomeration. The direct energy band gap was determined to be 3.18 eV. Furthermore, the PL (photoluminescence) emission spectra, CIE, and CCT coordinates strongly indicate high-intensity emission in the region of blue color. Dusting of powder reveals latent fingerprints. Synthesized SMI nanocomposite exhibits highly-resolved patterns in the form of ridges used to analyze specific latent fingerprints with clarity. Thus, the recently synthesized nanocomposite may have been used in forensics, fluorescence labeling, and blue light emission.

Visible-Light Photodetection by Zero-Dimensional Hybrid Indium-Halide with Minimal Structural Distortion and Reduced Band Gap.

Perovskite-inspired zero-dimensional (0D) hybrid halides exhibit impressive light emission properties; however, their potential in photovoltaics is hindered by the absence of interconnection between the inorganic polyhedra, leading to acute radiative recombination and insufficient charge separation. We demonstrate that incorporating closely-spaced dissimilar polyhedral units with minimal structural distortion leads to a remarkable enhancement in visible-light photodetection capability. We designed 0D C24H72N8In2Br14 (HIB) with a tetragonal crystal system, replacing the Cs+ of Cs2InBr5.H2O (CIB) with 1,6-hexanediammonium (HDA) cation. HIB comprises [InBr6]3- octahedra, and [InBr4]- tetrahedra units spaced 3.9 Å apart by the HDA linker. The [InBr4]- unit is additionally linked to HDA via intercalated bromine through hydrogen and halogen bonding interactions, respectively. This structural arrangement lowers the dielectric confinement, thereby enhancing carrier density and mobility, and increasing the diffusion coefficient compared to CIB. With 3.6 % bromine vacancy within the [InBr4]- block, mid-gap states are created, reducing the direct band gap to 2.19 eV. HIB demonstrates an unprecedently high responsivity of 9975.9±201.6 mA W-1 under 3 V potential bias at 485 nm wavelength, among low-dimensional hybrid halides. In the absence of potential bias, the self-powered photodetection parameters are 81.2±3.0 mA W-1 and (6.98±0.21)×109 Jones.

Visible‐Light Photodetection by Zero‐Dimensional Hybrid Indium‐Halide with Minimal Structural Distortion and Reduced Band Gap

AbstractPerovskite‐inspired zero‐dimensional (0D) hybrid halides exhibit impressive light emission properties; however, their potential in photovoltaics is hindered by the absence of interconnection between the inorganic polyhedra, leading to acute radiative recombination and insufficient charge separation. We demonstrate that incorporating closely‐spaced dissimilar polyhedral units with minimal structural distortion leads to a remarkable enhancement in visible‐light photodetection capability. We designed 0D C24H72N8In2Br14 (HIB) with a tetragonal crystal system, replacing the Cs+ of Cs2InBr5.H2O (CIB) with 1,6‐hexanediammonium (HDA) cation. HIB comprises [InBr6]3− octahedra, and [InBr4]− tetrahedra units spaced 3.9 Å apart by the HDA linker. The [InBr4]− unit is additionally linked to HDA via intercalated bromine through hydrogen and halogen bonding interactions, respectively. This structural arrangement lowers the dielectric confinement, thereby enhancing carrier density and mobility, and increasing the diffusion coefficient compared to CIB. With 3.6 % bromine vacancy within the [InBr4]− block, mid‐gap states are created, reducing the direct band gap to 2.19 eV. HIB demonstrates an unprecedently high responsivity of 9975.9±201.6 mA W−1 under 3 V potential bias at 485 nm wavelength, among low‐dimensional hybrid halides. In the absence of potential bias, the self‐powered photodetection parameters are 81.2±3.0 mA W−1 and (6.98±0.21)×109 Jones.

Enhancing thermoelectric and radiation shielding performance of novel LaFe0.8Mn0.2Sb12 skutterudites for energy applications

We explore the structural, optoelectronic, and thermoelectric properties of LaFe0.8Mn0.2Sb12 skutterudites using first-principles computations and semi-classical Boltzmann Transport equations. These materials are classified as semiconductors exhibiting band gaps of 0.55 eV and 1.8 eV for spin-up and down polarizations. Valence band maxima (VBM) and conduction band minima (CBM) lie on the gamma points, indicating direct band gaps for both spin channels. The band structure, density of states, and optical characteristics reveal that the material is a semiconductor. The optical reflectivity and complex dielectric function were calculated for a wide range of photon radiation to understand these compounds' optical properties. The transport parameters were investigated using electrical conductivity, thermal conductivity, the Seebeck coefficient, the power factor, the heat capacity, and the figure of merit determined using the Boltztrap code. The LaFe0.8Mn0.2Sb12 has a Seebeck coefficient of 5.77×10−6 V/K (Up), whereas the down channel has a 4.2×10−6 V/K. The highest figure of merit is 0.99, and as a result, the theoretical findings provide a robust foundation for upcoming experimental research. In this study, utilize the Phy-X program to evaluate the radiation shielding capabilities of LaFe0.8Mn0.2Sb12, focusing on critical parameters like mass attenuation coefficients (γmac) and half-value layers (γhvl), essential for optimizing protection against hazardous ionizing radiation. Computational study of energy-renewable and thermoelectric properties enables experimenters to investigate fresh applications for predicting photovoltaic materials with atomic-level accuracy.

Determining Bandgaps in the Layered Group‐10 2D Transition Metal Dichalcogenide PtSe2

AbstractUnlike traditional group‐6 transition metal dichalcogenides (TMDs), group‐10 TMDs such as PtSe2 and PdTe2 possess highly tuneable indirect bandgaps, transitioning from semiconducting in the near‐infrared to semimetal behavior with a number of monolayers (MLs). This opens up the possibility of TMD‐based mid‐infrared and terahertz optoelectronics. Despite this large potential, the optical properties of such materials have shown an extremely large disparity between that predicted and measured. For example, simulations show that a few MLs is required for the semiconductor–semimetal transition, whilst tens of MLs is found experimentally. This is a result of widely used optical extrapolation methods to determine bandgaps, such as the Tauc plot approach, that are not adapted here owing to i) nearby direct transitions, ii) the material dimensionality and iii) large changes in the non‐parabolic bandstructure with MLs. Here, uniquely combining optical ellipsometry to determine the complex permittivity, terahertz time resolved spectroscopy for the complex conductivity and in‐depth density functional theory (DFT) simulations, it is shown that the optical properties and bandstructure can be determined reliably and demonstrate clearly that the semiconductor‐semimetal transition occurs for PtSe2 layers ≈5 MLs. The microscopic origins of the observed transitions and the crucial role of the Coulomb interaction for thin semiconducting layers, and that of interlayer van der Waals forces for multilayer semimetallic samples are also demonstrated. This work of combining complimentary experimental techniques and extensive simulations avoids the application of constrained extrapolation methods to determine the optical properties of group‐10 TMDs, and will be of importance for future mid‐infrared and terahertz applications.

A THEORETICAL STUDY OF THE PHYSICAL PROPERTIES OF HEXAGONAL GALLIUM NITRATE USING DENSITY FUNCTIONAL THEORY

First-principles calculations based on density functional theory (DFT) have been used to investigate structural, electronic, optical and thermodynamic aspects of the α-GaN crystal. Based on local density approximations (LDA), Generalized gradient approximation (GGA) and meta-generalized gradient approximation (m-GGA) functional methods, the band gap energies of α-GaN crystals have been estimated as 1.962 eV, 2.069 eV and 2.354 eV. The band gap energies that are presented in these studies are in accordance with the ones from the other experimental and theoretical studies. Besides, our findings give us knowledge about the electronic and optical properties of α-GaN crystal. The band gap energies in the α-GaN crystal are the key factors that define its electrical and optical characteristics. They are the energy range in which the electrons can be exited from the valence band to the conduction band, which in turn affects the material's conductivity and the ability of the material to absorb and emit light. The approximate of our results with the previous researches indicates the reliability of our findings and thus increases our knowledge of α-GaN's electronic and optical phenomena. The orbital characteristics of the Ga and N atoms were found by simulating the density of state and the partial density of state for α-GaN. Besides the analysis of the band structure, density of states and optical properties of the compound we also included. The results show that α-GaN has a direct bandgap, which is at the G point in the Brillouin zone. This is the reason for its great potential for the development of optoelectronic devices. Also, we use the three approximations that are given earlier to find the optical characteristics (the absorption coefficient) of the compound. In addition to that, the thermodynamic properties that can be calculated like Debye temperature, enthalpy, free energy, entropy and heat capacity enable us to understand the thermal behavior of the compound better. The heat capacity of α-GaN is detected to be 17.3 Jmole-1K-1, with a Debye temperature of 824.6K. This research will offer a detailed interpretation of α- G-N, covering all its basic properties and the possible applications in optoelectronic and electronic devices. The results of this study are very important and the new technologies that will be developed based on the α-GaN research will be very beneficial.

From layered 2D carbon to 3D tetrahedral allotropes C12 and C18 with physical properties related to diamond: Crystal chemistry and DFT investigations

Mechanisms of changes from 2D to 3D (D = dimensionality) involving 2D C(sp2) trigonal paving to C(sp3) tetrahedral stacking are proposed through puckering of the 2D layers on one hand and interlayer insertion of extra C on the other hand. Such transformations, led to 3D hexagonal C12 and C18 allotropes respectively characterized by lon and bac topologies. Using density functional theory DFT calculations, the two allotropes were found cohesive and stable both mechanically (elastic properties) and dynamically (phonons). Comparisons of the physical properties with known uni C6 were established letting identify ranges of large Vickers hardness: HV (uni C6) = 89 GPa, HV (lon C12) = 97 GPa, and HV (bac C18) = 70 GPa. Whilst C6 was identified with acoustic phonons instability, C12 and C18 were found stable dynamically throughout the acoustic and optic frequency ranges. Furthering on the thermal properties the allotropes were characterized with a temperature dependence curve of the specific heat CV close to experimental data of diamond with best fit for novel C18. The electronic band structures reveal a small band gap of 1 eV for uni C6 and larger direct band gap of 3 eV for the two other 3D allotropes. Such modulations of the electronic and physical properties should open scopes of carbon research.

Low-pressure superconductivity of Th-B-H ternary compounds: An insightful study of stable and metastable phases

The low-enthalpy structures of Th-B-H ternary compounds below 50 GPa are investigated by using an efficient framework that combines high-throughput screening, genetic algorithms, and first-principles calculations. Four thermodynamically stable hydrides (Th2BH11, Th2BH10, ThB2H10, and ThBH) and seven thermodynamically metastable hydrides (ThBH2, ThBH3, ThBH4, ThBH5, ThBH7, ThB2H4, and ThB3H3) are revealed. There are no stable thorium boron hydrides at ambient pressure. R3m-ThB2H10 and R3m-Th2BH11 are indirect bandgap semiconductors, while R3m-Th2BH10 and P6/mmm-ThBH show metallic nature. The relatively low λ values of R3m-Th2BH10 and P6/mmm-ThBH result in their Tc around 5.8 K and 0.1 K at 20 GPa, respectively. Two metastable phases, F4¯3m-ThBH5 and P63/mmc-ThBH7, exhibit excellent superconducting properties at low pressures. The values of Tc of F4¯3m-ThBH5 and P63/mmc-ThBH7 reach 46.9 K at 20 GPa and 40.0 K at 50 GPa, respectively. Our findings offer valuable insights for discovering and designing superconducting rare earth hydrides under low and even ambient pressures.

On the absorption coefficient of GaP1-xNx layers and its potential application for silicon photovoltaics

The absorption coefficient and the energy gap of GaP1-xNx layers has been obtained by spectroscopic ellipsometry for samples grown on Si(001) substrates by chemical beam epitaxy with N mole fractions in the range 0 ≤ x ≤ 0.081. The resulting absorption spectra exhibit a direct band-like behavior near the absorption edge. The absorption coefficient values increase with the N content, reaching values in the range α ∼ 1-2x104 cm−1 in the vicinity of the absorption edge below the original GaP direct bandgap, which are comparable to those obtained for high efficiency solar cell materials. Furthermore, dependence of the absorption coefficient with increasing N content points to a strong GaP Γ-like character of the conduction-band wave function of GaP1-xNx alloys near the Brillouin zone center at k = 0, as predicted by the band anticrossing model. Bandgap energy values obtained by spectroscopic ellipsometry are compared with previous values obtained by photoluminescence measurements on the same samples, observing a shift of about 50–100 meV. Finally, the value of the band anticrossing parameter coupling the N level and the host GaP conduction band has been obtained from the dependence of both, the bandgap and the absorption coefficient, with the N content (2.1 and 3.3 eV respectively).

Abnormal Response of Indirect Excitons to Non‐Uniform Elastic Strain in MoS2 Flakes

AbstractRegulating the electronic structures and carrier dynamics in 2D materials via elastic strain is a fascinating avenue for tailoring their optoelectronic properties at atomic scale. Here, the abnormal response of indirect excitons to non‐uniform elastic strain in MoS2 flakes is reported. The non‐uniform elastic strain in the MoS2 flakes is introduced by transferring them to pre‐prepared convex cross structures on a SiO2/Si substrate, where the topography and strain distribution are determined by atomic force microscopy and Raman spectroscopy, respectively. It is observed that the emission energy of the indirect excitons shows an unexpected blue‐shift followed by a red‐shift with increasing the local tensile strain, which is in sharp contrast to the linear red‐shift of the direct excitons. Density functional theory calculations reveal that the abnormal energy shift of the indirect excitons in the MoS2 flakes arises from the strain‐induced competition between two indirect bandgap transitions and the spatial exciton funnel effect in the non‐uniform strain field. This work provides new insights into the elastic strain effect on the indirect excitons in 2D semiconductors, which possesses potential applications in flexible optoelectronic devices.

Enchanting optical, electronic, and mechanical properties of the sodium based Na2MgSiZ6 (Z = I, Br, Cl) halides have been explored through DFT

Materials. with perovskite structures have been extensively studied due to their remarkable properties, which are important in various aspects of daily life. In the present approach, Na2MgSiZ6 (Z = I, Br, Cl) halides were extensively studied, and it was realized from the band structure results that all these halides display semiconducting natures with indirect band gaps. The semiconducting natures of Na2MgSiZ6 (Z = I, Br, Cl) halides were further confirmed by their TDOS results. The optimized values of the lattice constants were found to be 11.70 Å, 10.4 Å, and 10.22 Å for Na2MgSiI6, Na2MgSiBr6, and Na2MgSiCl6, respectively. Moreover, the largest volume was observed for the Na2MgSiI6 compound, while the smallest volume was recorded for the Na2MgSiCl6 compound. Na2MgSiCl6 compound exhibited brittle nature, whereas Na2MgSiBr6 and Na2MgSiI6 were found to be ductile. All three materials demonstrated attractive values of optical conductivities, making them befitting candidates for solar cells, LEDs, detectors, and various other optoelectronic devices. From the achieved negative values of formation energy for all the Na2MgSiZ6 (Z = I, Br, Cl) halides, it was comprehended that these compounds could be synthesized practically.