Direct Electronic Band Gap Research Articles

Unveiling the structural and optoelectronic properties of (P, Bi, Sb)-doped GaAs by first- principles calculations

In this work, we investigate the influence of M substitutions (M = P, Bi, and Sb) on the structural, electronic, and optical properties of gallium arsenide, GaM x As1-x for x=0,0.25,0.50,0.75,1.0 using density functional theory (DFT). We have observed that the cubic symmetry of the semiconductors in conserved, and lattice constants show a linear behavior with dopant concentration, according to Vegard’s law. Specifically, the lattice constants increased for Bi and Sb dopants, whilst decreased for P dopants. Furthermore, the bulk modulus decreased with an increase in M-concentration for all M-doped systems. The energy analysis showed that the P-doped system was the most stable system. In terms of the electronic band structure, all M-doped compounds exhibited a direct electronic band gap. The P-doped system showed a wide band gap, while the Sb-doped systems displayed a narrow band gap, both compared to pristine GaAs. The Bi-doped system showed metallic-like behavior. To gain insights into the linear optical properties of the GaM x As1-x compounds, we calculated the real and imaginary parts of the dielectric function, as well as other optical parameters such as the absorption coefficient, refractive index, extinction coefficient, and reflectivity. The results showed that P doping leads to a blue-shift in the optical absorption coefficient, while Bi and Sb doping lead to a red-shift. These findings provide valuable theoretical insights for the potential application of GaM x As1-x semiconductors in photovoltaics and optoelectronic devices.

Electrocatalytic Performance of 2D Monolayer WSeTe Janus Transition Metal Dichalcogenide for Highly Efficient H2 Evolution Reaction.

Nowadays, the development of clean and green energy sources is the priority interest of research due to increasing global energy demand and extensive usage of fossil fuels, which create pollutants. Hydrogen has the highest energy density by weight among all chemical fuels. For the commercial-scale production of hydrogen, water electrolysis is the best method, which requires an efficient, cost-effective, and earth-abundant electrocatalyst. Recent studies have shown that the 2D Janus transition metal dichalcogenides (JTMDs) are promising materials for use as electrocatalysts and are highly effective for electrocatalytic H2 evolution reaction (HER). Here, we report a 2D monolayer WSeTe JTMD, which is highly effective toward HER. We have studied the electronic properties of 2D monolayer WSeTe JTMD using the periodic hybrid DFT-D method, and a direct electronic band gap of 2.39 eV was obtained. We have explored the HER pathways, mechanisms, and intermediates, including various transition state (TS) structures (Volmer TS, i.e., H*-migration TS, Heyrovsky TS, and Tafel TS) using a molecular cluster model of the subject JTMD noted as W10Se9Te12. The present calculations reveal that the 2D monolayer WSeTe JTMD is a potential electrocatalyst for HER. It has the lowest energy barriers for all the TSs among other TMDs. It has been shown that the Heyrovsky energy barrier (= 8.72 kcal mol-1) in the case of the Volmer-Heyrovsky mechanism is larger than the Tafel energy barrier (= 3.27 kcal mol-1) in the Volmer-Tafel mechanism. Hence, our present study suggests that the formation of H2 is energetically more favorable via the Volmer-Tafel mechanism. This study helps to shed light on the rational design of 2D single-layer JTMD, which is highly effective toward HER, and we expect that the present work can be further extended to other JTMDs to find out the improved electrocatalytic performance.

Effect of cobalt doping on the structural, magnetic, optical, and electronic properties of LiFeCr4O8

Cobalt doping's influence on the structural, magnetic, and electronic properties of the double spinel LiFeCr4O8 was systematically investigated. Rietveld refinement revealed a consistent increase in lattice parameter a and unit cell volume with cobalt incorporation. Magnetic susceptibility measurements indicated three distinct transitions: an increase in the ferrimagnetic transition temperature (TN), a decrease in the magnetostructural transition temperature (TMS), and an increase in the spin gap transition by cobalt doping. Through diffuse reflectance spectroscopy the direct optical band gap (Eog) was obtained with values of 1.169 eV, 1.303 eV, 1.396 eV, and 1.230 eV for x = 0.0, 0.1, 0.2, and 0.5, respectively. The observed increase in Eog with cobalt doping suggests a widening of the band gap, which could be beneficial for optoelectronic applications. By means of X-ray photoelectron spectroscopy (XPS) the core levels of Li 1s, Co 3p, Fe 3p, Cr 3p, Fe 2p, Cr 2p, and O 1s were identified. XPS valence band (VB) analysis revealed a decreasing intensity at binding energy BE = 0 eV with respect to x = 0.0. Density functional theory calculations with Hubbard U correction (DFT + U) confirmed a ferrimagnetic semiconductor behavior with a direct electronic band gap (Eeg) of 1.085 eV.

Understanding the Electronic Structure and Chemical Bonding in the 2D Fullerene Monolayer.

Recently synthesized two-dimensional (2D) monolayer quasi-hexagonal-phase fullerene (qHPC60) demonstrates excellent thermodynamic stability. Within this monolayer, each fullerene cluster is surrounded by six adjacent C60 cages along an equatorial plane and is connected by both C-C single bonds and [2 + 2] cycloaddition bonds that serve as bridges. In this study, we investigate the stability mechanism of the 2D qHPC60 monolayer by examining the electronic structure and chemical bonding through state-of-the-art theoretical methodologies. Density functional theory (DFT) studies reveal that 2D qHPC60 possesses a moderate direct electronic band gap of 1.46 eV, close to the experimental value (1.6 eV). It is found that the intermolecular bridge bonds play a crucial role in enhancing the charge flow and redistribution among C60 cages, leading to the formation of dual π-aromaticity within the C60 sphere and stabilizing the 2D framework structure. Furthermore, we identify a series of delocalized superatom molecular orbitals (SAMOs) within the 2D qHPC60 monolayer, exhibiting atomic orbital-like behavior and hybridization to form nearly free-electron (NFE) bands with σ/π bonding and σ*/π* antibonding properties. Our findings provide insights into the design and potential applications of NFE bands derived from SAMOs in 2D qHPC60 monolayers.

Effect of Ni-doping on the structural and electronic properties of metal halide perovskite CsSnBr3: a DFT study

The structural and electronic properties of pure and Ni-doped perovskite CsSnBr3 in unit cell and supercell were computed using density functional theory at ambient pressure. Computed formation energy values of undoped and Ni-doped CsSnBr3 compounds show that these structures are stable. We used both standard DFT and HSE06 calculation in electronic band structure of pure and Ni-doped CsSnBr3 compounds. Since the band gap of undoped and Ni-doped CsSnBr3 compounds is located at the R symmetry point in the Brilloun zone, these compounds are materials with a direct band gap. In the HSE06 calculation, it was found that the band gap of 12.5% Ni doped-CsSnBr3 increased significantly from 1.1162 eV to 1.4343 eV. The electron charge density, Bader charge analysis and density of states reveal a strong covalent bond between Sn-Br (Ni-Br) and a strong ionic bond between Cs-Br. The direct electronic band gaps of undoped and Ni-doped CsSnBr3 perovskites in the visible energy range show that these compounds can be used effectively in optical applications.

On the mechanical, thermoelectric, and excitonic properties of Tetragraphene monolayer

Two-dimensional carbon allotropes have attracted much attention due to their extraordinary optoelectronic and mechanical properties, which can be exploited for energy conversion and storage applications. In this work, we use density functional theory simulations and semi-empirical methods to investigate the mechanical, thermoelectric, and excitonic properties of Tetrahexcarbon (also known as Tetragraphene). This quasi-2D carbon allotrope exhibits a combination of squared and hexagonal rings in a buckled shape. Our findings reveal that tetragraphene is a semiconductor material with a direct electronic bandgap of 2.66eV. Despite the direct nature of the electronic band structure, this material has an indirect exciton ground state of 2.30eV, which results in an exciton binding energy of 0.36eV. At ambient temperature, we obtain that the lattice thermal conductivity (κL) for tetragraphene is approximately 118 W/mK. Young’s modulus and the shear modulus of tetragraphene are almost isotropic, with maximum values of 286.0N/m and 133.7N/m, respectively, while exhibiting a very low anisotropic Poisson ratio value of 0.09.

(Invited) Atomic Layer Processing of MoS2

Molybdenum disulfide (MoS2) is one of several transition metal dichalcogenides consisting of a layer of transition atoms sandwiched between layers of chalcogens. Interest in MoS2 has been driven by its 1.8 eV direct electronic band gap in monolayer form and its moderate electron mobility (10-100 cm2/Vs) even when only three atoms (~6.5 Å) thick. These properties offer potential for retaining or improving speed and efficiency in scaled electronic devices.Advancing MoS2 and other 2D materials into high volume manufacturing of semiconductor devices requires scalable deposition and etching processes. The process of atomic layer deposition (ALD) has been used to deposit 2D materials and can deposit films at lower temperatures for back-end-of-line (BEOL) compatibility. However, ALD relies on covalent surface reactions. When these reactions occur at high density during film nucleation, the resulting film is typically amorphous or nanocrystalline and requires thermal annealing to form a more well-ordered layered crystal structure. A key challenge is to establish a low temperature ALD process that achieves a layered crystal structure with low defectivity. In terms of material removal, MoS2 films have been etched by plasma-based atomic layer etching (ALE). ALE is analogous to ALD except that cyclic surface reactions promote volatility and lead to film removal rather than deposition. Together, atomic layer deposition and atomic layer etching constitute complementary facets of atomic layer processing and enable new pathways for nanomanufacturing.Here, we describe our recent progress in thermal ALD and thermal ALE of MoS2 films. For ALD of MoS2, we use cycles of MoF6 and H2S between 150-350 °C. Nucleation on metal oxide surfaces shows a strong temperature dependence, which is attributed in part due to the temperature dependence of surface hydroxyl groups. Density functional theory (DFT) calculations support the role of hydroxyls in promoting nucleation and reveal that MoF6 dissociates on the surface rather than participating in a ligand exchange reaction. The dissociation reaction leads to the formation of a metal fluoride interface between the oxide surface and the MoS2 film. Surface species following MoF6 include MoOF4 and MoO3, both of which convert to MoS2 during the H2S pulse, which releases H2O and HF byproducts. Films deposited at 200 °C and below are amorphous but convert to a layered structure upon annealing in H2S. Deposition at 250 °C yields films with a layered crystal structure without post-deposition annealing.Thermal ALE of MoS2 films deposited by ALD can be achieved using alternating exposures of MoF6 and H2O. It was found that MoS2 films are fluorinated by the MoF6 and then oxygenated by H2O. Volatile byproducts are MoF2O2, H2S, and HF, which are primarily released during the H2O half-cycle. Thermal ALE of MoS2 is temperature dependent and follows Arrhenius behavior. At 200 °C, the mass loss per cycle is 6 ng/cm2 (~0.5 Å/cycle) and reaches 271 ng/cm2 at 300 °C. Etch stop behavior was observed once the etched film approached the metal fluoride interface of the growth surface. Layered MoS2 deposited by ALD with post-deposition annealing exhibited layer-by-layer etching at 0.2 Å/cycle at 250 °C.The ALD results provide key insights into the nucleation and growth of MoS2 films using low temperature ALD. Further work is required to control basal plane orientation but achieving crystalline films well within BEOL thermal budgets is promising. The results from the ALE study provide insights into the etching reactions for MoS2. Combining the two processes offers greater control over MoS2 films. Using ALD followed by ALE and post-deposition annealing, we achieved few-layer MoS2 films. These combined thermal processes represent a pathway for integration of MoS2 films into device manufacturing.

Can Lead-Free Double Halide Perovskites Serve as Proper Photovoltaic Absorber?

The emerging Pb-free double perovskites (DPs) are acknowledged as the most potential nontoxic alternatives to lead halide perovskites for thin-film photovoltaics, yet their photophysical properties significantly lag behind expectations. To tackle this issue, it is imperative to conduct a systematic investigation of the structure and optoelectronic properties and to sift through vast chemical space to extract new types of Pb-free DPs with exceptional optoelectronic characteristics and thermal stability. Through high-throughput first-principal calculations, we demonstrate that apart from a select few Pb-free DPs (e.g., Cs2InSbCl6 and Cs2TlBiBr6), other categories, even with suitable direct electronic bandgaps, exhibit inferior optical absorption due to the inversion symmetry-induced parity-forbidden transitions. The mismatch between the electronic and optical bandgap, thence, casts doubt on the reliability of the electronic bandgap as a criterion for Pb-free DPs in various optoelectronics. The assessed limited thermostability under operational conditions, however, hinders any Pb-free DPs from effectively serving as photovoltaic absorbers. Alongside the compositional engineering discussed above, the prospect of manipulating local-site symmetry and disrupting the parity forbidden transitions in stabilized Pb-free DPs through materials engineering should be recognized as a pivotal and rational avenue toward achieving high performance.

Structural polymorphism, electronic, and optical properties of NaSbS2: A computational approach toward eco-friendly and emerging semiconductor

In this work, the structural polymorphism and electro-optical characteristics of NaSbS2 ternary chalcogenide are realized using density functional theory (DFT). All of the NaSbS2 polymorphs are energetically stable based on the formation energy. The optimized lattice parameters of the monoclinic and triclinic structures and direct electronic bandgap (1.695 eV) of monoclinic structure are consistent with previous studies. Besides, the trigonal and triclinic structures are indirect bandgap (0.916 and 2.015 eV) semiconductors observed from electronic band structure. The higher degree of ionicity between Na and S atoms while strong covalency in the Sb-S bonds are confirmed from the charge and bond analysis. The lower value of electron-hole effective masses indicates higher carrier mobility leading to outstanding electrical conductivity. It was suggested that the polymorphs would be extremely desired to design Bragg reflectors and waveguides based on the reported high value of the real part of the dielectric constant and refractive index. These polymorphs will contribute significantly to being used as absorbers, as evidenced by their high absorption coefficient and photoconductivity and lower transmittance. All the polymorphs reflect significant optical anisotropy and birefringence, rendering them excellent for usage in the fabrication of waveguides, polarizers, and photonic devices. Thus, the projected good features of NaSbS2 polymorphs would play an essential role in the development of lead-free photovoltaic devices, including solar cells and other optoelectronic devices, and would be able to provide practical information for future theoretical and experimental studies.

The effect of pressure on the band-gap energy in FePO[formula omitted] and FeVO[formula omitted

In this work, we have studied the electronic structure of FePO4 and FeVO4 under high pressure by means of optical-absorption measurements and first-principles calculations. Samples of both compounds have been pressurized up to 6 GPa within a diamond-anvil cell to be characterized in the ultraviolet–visible-near infrared range. The optical-absorption measurements corroborated previously reported phase transitions: berlinite (P3121) ⟶ CrVO4-type (Cmcm) in FePO4, and FeVO4-I (P1̄) ⟶ FeVO4-I’ (P1̄) ⟶ FeVO4-II’ (α-MnMoO4-type, C2/m) in FeVO4. According to our experiments, FePO4 presents direct electronic band-gaps in both phases. In contrast, the low- and high-pressure phases of FeVO4 have indirect band-gaps. In both compounds, the band-gap energy decreases with pressure. The computed electronic band structure revealed that the population at valence band maxima (VBM) and conduction band minima (CBM) changes with pressure in both FePO4 and FeVO4. Pressure-induced changes in Fe coordination modulate the occupation at VBM and CBM, being more pronounced the consequences in FePO4 due to the shift from tetrahedral (FeO4) to octahedral (FeO6) coordination. We have also analyzed the charge density within the quantum theory of atoms in molecules (QTAIM) methodology to complement the electronic structure results by computing the Bader effective charges, the Laplacian, and ellipticity at the bond critical points for both compounds as a function of pressure.

Planar buckling controlled optical conductivity of SiC monolayer from Deep-UV to visible light region: A first-principles study

The electrical and optical properties of flat and planar buckled siligraphene (SiC) monolayer are examined using a first principles approach. Buckling between the Si and the C atoms in SiC structures influences and impacts the properties of the 2D nanomaterial, according to our results. The electron density of a planar SiC monolayer is calculated, as well as the effects of buckling on it. According to our findings, a siligraphene monolayer is a semiconductor nanomaterial with a direct electronic band gap that decreases as the planar buckling rises. The contributions to the density of states differ owing to changes in the system’s structure. Another explanation is that planar buckling reduces the sp2 overlapping, breaking the bond symmetry causing it to become a sp3 bond. We show that increased planar buckling between the Si and the C atoms alters the monolayer’s optical, mechanical, and thermal properties. A managed planar buckling increases the optical conductivity with a significant shift in the far visible range, as all optical spectra features are red shifted, still remaining visible. Instead of a σ-σ covalent bond, the sp3 hybridization produces a stronger σ-π bond. Optical characteristics such as the dielectric function, the absorbance, and the optical conductivity of a SiC monolayer are investigated for both parallel and perpendicular polarization of the incoming electric field for both flat and planar buckled systems. The findings show that the optical properties are influenced for both of these two polarizations, with a significant change in the optical spectrum from the near visible to the far visible. The ability to manipulate the optical and electrical characteristics of this critical 2D material through planar buckling opens up new technological possibilities, especially for optoelectronic devices.

DFT crystal and electronic structure of the direct bandgap Cu(1-x)NaxPF6: (x = 0.125n, n = 1–7)

DFT study on the crystal and electronic structure of the hexafluorophosphates Cu(1-x)NaxPF6 (x = 0.125n, n = 1–7) is presented. Both parent compounds CuPF6 and NaPF6 constituting the co-crystals have the same (FCC) spatial symmetry, very similar lattice constants (Δa = 0.017 Å), and according to periodic PBE density functional computations possess direct electronic bandgaps of 0.82 eV and 8.01 eV, respectively. Geometry optimization of the co-crystals Cu(1-x)NaxPF6 (x = 0.125n, n = 1–7) retain FCC symmetry. All the resulting electronic bandgaps are direct. Their values are intermediate between those of the parent compounds falling into the range from 0.97 eV (Cu0.875Na0.125PF6) to 2.22 eV (Cu0.125Na0.875PF6). All the compounds feature very small hole velocities. In contrast, electron velocities are high varying from 2.05*105 m/s (Cu0.875Na0.125PF6) to 1.12*105 m/s (Cu0.125Na0.875PF6) and showing descending trend as the content of sodium in the co-crystals increases. Taking into account the values of direct electronic bandgaps and presumed poor solubility in water the co-crystals seem good candidates for solar light harvesting applications.

A simple and robust machine learning assisted process flow for the layer number identification of TMDs using optical contrast spectroscopy

Layered transition metal dichalcogenides (TMDs) like tungsten disulphide (WS2) possess a large direct electronic band gap (∼2 eV) in the monolayer limit, making them ideal candidates for opto-electronic applications. The size and nature of the bandgap is strongly dependent on the number of layers. However, different TMDs require different experimental tools under specific conditions to accurately determine the number of layers. Here, we identify the number of layers of WS2 exfoliated on top of SiO2/Si wafer from optical images using the variation of optical contrast with thickness. Optical contrast is a universal feature that can be easily extracted from digital images. But fine variations in the optical images due to different capturing conditions often lead to inaccurate layer number determination. In this paper, we have implemented a simple Machine Learning assisted image processing workflow that uses image segmentation to eliminate this difficulty. The workflow developed for WS2 is also demonstrated on MoS2, graphene and h–BN, showing its applicability across various classes of 2D materials. A graphical user interface is provided to enhance the adoption of this technique in the 2D materials research community.

Structures, stabilities, optoelectronic and photocatalytic properties of Janus aluminium mono-chalcogenides Al(Ga, In)STe monolayers

Computational design of new two-dimensional materials constitutes an effective and promising approach in the development and exploration of a wide range of emerging applications such as optoelectronics, photocatalysis, energy storage, and conversion. Within the framework of this work, we systematically investigated for the first time, the structural, stability, optoelectronic, and pho-tocatalytic properties of new predicted Al(Ga, In)STe monolayers derived from Janus Aluminium mono-chalcogenides through Density Functional Theory and Ab-Initio molecular dynamic simulations. After a full optimization of both struc-tures, their dynamics and thermal stability was confirmed through the calculations of phonon spectrum and ab-initio molecular dynamics at a chosen temperature, respectively. Subsequently, the electronic and optical properties were explored and findings revealed that both monolayers exhibit a semiconducting characteristic with a direct and indirect electronic band gap of about 2.23 and 2.69 eV using HSE06 hybrid functional for AlGaSTe and AlInSTe monolayers, re-spectively. Furthermore, the optical absorption indicates a strong absorption of light in the range between 3 and 18 eV. More noticeably, Both Janus monolayers considered exhibiting a promising optical absorption in the visible wavelength region with an absorption coefficient greater than 105 cm−1. In addition, the photocatalytic properties of these structures were investigated by plotting the band edge positions straddle the reduction potential of H2 and the oxidation potential H2O. Based on our results, we conclude that both monolayers offer good thermodynamic stability allowing them to be processed experimentally and can be used as very appropriate candidates for optoelectronics and photocatalytic applications.

A DFT study of the electronic, optical, and mechanical properties of a recently synthesized monolayer fullerene network

Closely packed quasi-hexagonal and quasi-tetragonal crystalline phase of C60 molecules (named qHPC60) was recently synthesized. Here, we used GGA-PBE based DFT simulations to investigate the optoelectronic and mechanical properties of qHPC60 monolayers. qHPC60 has a moderate direct electronic bandgap, with anisotropic mechanical properties. Their elastic modulus ranges between 50–62 GPa. The results for optical properties suggest that qHPC60 can act as a UV collector for photon energies up to 5.5 eV since it presents low reflectivity and refractive index greater than one. The estimated optical bandgap (1.5–1.6 eV) is in very good agreement with the experimental one (1.6 eV).

Ab initio study of K[formula omitted]Cu[formula omitted]P[formula omitted] material for photovoltaic applications

Search for efficient materials for application in the fields of optoelectronics and photovoltaics are some of the most active areas of research across the world. The potential of compounds such as K3Cu3P2 is not yet fully realized. The ab initio studies based on density functional theory (DFT) to investigate the structural, electronic, elastic, and optical properties of K3Cu3P2 have been performed. Ground state properties have been computed in three different scenarios, i.e: with spin–orbit coupling (SOC), without spin–orbit coupling, and with the Hubbard U parameter. Direct electronic bandgaps of 1.338 eV, 1.323 eV, and 1.673 eV has been obtained for K3Cu3P2 without SOC, K3Cu3P2 with SOC and K3Cu3P2 with Hubbard U, respectively. In all the cases, Cu-d orbitals have been observed to be dominant at the top of the valence band. The effect of SOC on the K3Cu3P2 computed lattice constant, and bandgap has been found to be insignificant. The mechanical stability test revealed that K3Cu3P2 is mechanically stable at zero pressure. The optical band gap has been found to increase by 0.635 eV when Hubbard U is taken into consideration. Generally, the inclusion of the Hubbard U parameter in density functional theory improves the predictions of the bandgap and optical properties.

Structure and electronic properties of LnScO3 compounds: A GGA + U calculation

The lattice parameters, bond lengths, bond angles (octahedra tilt angles), Goldschmidt tolerance factor, density of states and electronic band structure of rare-earth scandates LnScO3 (Ln = Eu, La, Nd, Pr, Sm and Tb) in orthorhombic structure have been investigated in the generalized gradient approximation (GGA) + U method with the on-site Coulomb interaction parameter Ueff varying from 1 to 10 eV. The lattice constants, octahedra tilt angles (except for (Eu,Tb)ScO3 compounds), mean 〈Sc-O〉 and 〈Ln-O〉 bond lengths increased almost linearly with effective U parameter values. However, the tolerance factor has decreased (except for (Eu,Tb)ScO3 compounds). Density of states and electronic band structure computations show that LnScO3 compounds are insulator materials and have direct electronic band gap. The electronic band gap of the compounds first increases and then decreases with increasing Ueff. (GGA) + U calculation shows a strong hybridization between Sc-3d and O-2p states. Rare-earth (Ln)-5d states contribute somewhat to this hybridization. The electronic charge distribution and (P)DOS calculation results show that the bonding behavior of LnScO3 compound is a combination of covalent and ionic nature. Our results show that the structural and electronic properties are affected by the application of the Hubbard U term in GGA calculations and the computed lattice constants, bond distances and octahedra tilt angles deviate more from the experimental values. On the other hand, it was observed that the electronic band gap approached the experimental values at the optimal Ueff values determined for the compounds.

Two-Dimensional Janus GePAs Monolayer: A Direct-Band-Gap Semiconductor with High and Anisotropic Mobility for Efficient Photocatalytic Water Splitting

Two-dimensional (2D) materials with suitable electronic and optical properties offer various possibilities for photocatalytic applications. Although various 2D materials have hitherto been specified as adequate candidates, materials with high photocatalytic efficiency for water splitting are still minimal. In this study, we predict a 2D Janus $\mathrm{Ge}\mathrm{P}\mathrm{As}$ monolayer and examine its capability for photocatalytic water splitting by performing first-principles calculations. The $\mathrm{Ge}\mathrm{P}\mathrm{As}$ monolayer is shown to possess robust dynamic and thermal stability. The direct electronic band gap in the visible region and band-edge positions of the strain-free and strained monolayers are revealed to be convenient for redox reactions in wide pH ranges. The low recombination probability of charge carriers ensured by high and anisotropic carrier mobility enhances the material's photocatalytic potential. Optical response calculations, including many-body interactions, indicate significant optical absorption capacity in the UV-visible range. Furthermore, low exciton binding energy facilitates dissociation into free electrons and holes, promoting photocatalytic reactions. Our study suggests that the $\mathrm{Ge}\mathrm{P}\mathrm{As}$ monolayer is an ideal and remarkably promising material to be utilized in visible-light-driven photocatalytic applications.

Theoretical insight into electronic and optical behaviour of H-adsorbed Zn-terminated Zn3N2-(100)-non-polar surface

Present paper deals with the study of electronic and optical behaviour of a II3-V2 group semiconductor compound Zn3N2 and corresponding significant alterations, that are realised after H-adsorption on its (100) non-polar surface. Calculations are performed applying the linear combination of atomic orbitals method. The relative stability of H-adsorbed systems represents the adsorption to be energetically favourable, indicating possible applications in H-storage devices. A direct electronic band gap of 1.59 eV at gamma point is reported, which is further converted into conducting and again semiconducting for slab and adsorbed configurations, respectively. This tuning of the band gap is very important outcome that may emerge new possibilities in optoelectronic field. Further, favourable alterations are perceived in optical behaviour as well, allowing more absorption possibilities in the optimum range of solar radiations. Consequently, efficiencies are supposed to get enhanced.

Fingerprints of optical absorption in the perovskite LaInO3 : Insight from many-body theory and experiment

We provide a combined theoretical and experimental study of the electronic structure and the optical absorption edge of the orthorhombic perovskite LaInO$_{3}$. Employing density-functional theory and many-body perturbation theory, we predict a direct electronic quasiparticle band gap of about 5 eV and an effective electron (hole) mass of 0.31 (0.48) m$_{0}$. We find the lowest-energy excitation at 0.2 eV below the fundamental gap, reflecting a sizeable electron-hole attraction. Since the transition from the valence band maximum (VBM, $\Gamma$ point) is, however, dipole forbidden the onset is characterized by weak excitations from transitions around it. The first intense excitation appears about 0.32 eV above. Interestingly, this value coincides with an experimental value obtained by ellipsometry (4.80 eV) which is higher than the onset from optical absorption spectroscopy (4.35 eV). The latter discrepancy is attributed to the fact that the weak transitions that define the optical gap are not resolved by the ellipsometry measurement. The absorption edge shows a strong dependency on the light polarization, reflecting the character of the involved valence states. Temperature-dependent measurements show a redshift of the optical gap by about 120 meV by increasing the temperature from 5 to 300 K. Renormalization due to zero-point vibrations is extrapolated from the latter measurement to amount to 150 meV. By adding the excitonic binding energy of 0.2 eV obtained theoretically to the experimental optical absorption onset, we determine the fundamental band gap at room temperature to be 4.55 eV.