Indirect Band Gap Semiconductor Research Articles

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.

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.

Modulated bandgap and gas adsorption behavior on two-dimensional SrAl2S4 monolayer: Potential applications for photovoltaic and energy storage

The structure of a novel two-dimensional layered material SrAl2S4 monolayer has been proposed, and its kinetic and thermodynamic stability has been confirmed. Researches have shown that SrAl2S4 monolayer is a semiconductor material with a bandgap of 1.630 eV for PBE and 2.798 eV for HSE06 at the ground state. Under biaxial strain, SrAl2S4 monolayer can complete the transition from a direct bandgap semiconductor to an indirect bandgap semiconductor, and its bandgap can vary between 0.187 eV and 1.712 eV. In addition, We have considered the adsorption behavior of SrAl2S4 monolayer for hydrogen and oxygen molecules, and the results show that SrAl2S4 monolayer adsorbed H2 molecules remains a direct bandgap semiconductor, whereas SrAl2S4 monolayer adsorbed O2 molecules show indirect bandgap semiconductor properties. At the same time, the adsorption of O2 molecules causes a flat band near the Fermi level, which increases the electrical conductivity. The few charges transfer observed between the SrAl2S4 monolayer and gas molecules confirms that the adsorption process of gas molecules on SrAl2S4 monolayer is physical adsorption. The tunable bandgap characteristics and good adsorption behavior of hydrogen and oxygen exhibited by SrAl2S4 monolayer make it a promising candidate material in the fields of photovoltaics and energy storage.

Optoelectronic properties of mechanically stable cubic Niobate compounds under hydrostatic pressure: A systematic DFT investigation

Perovskite oxides, particularly cubic Niobate compounds, have been studied for their potential application in the development of optoelectronic devices. The mechanical stability of these compounds has been verified by determining their elastic constants. Based on an analysis of their electronic band structures and densities of states, it has been found that both compounds exhibit non-magnetic behavior and possess properties typical of indirect bandgap semiconductors. The bandgap energies of the compounds are 1.524 eV and 1.392 eV, respectively. The optical properties of the compounds are analyzed under varying hydrostatic pressure conditions. Bandgap modulation results in a shift in absorption spectra from ultraviolet to visible wavelengths, rendering the materials appropriate for use in optoelectronic devices. Perovskites with (K,Rb)NbO3 exhibit potential as non-magnetic indirect bandgap semiconductors for the advancement of optoelectronic devices.

The structural, stability, electronic, optical and thermodynamic properties of Ba2AsXO6（X = V, Nb, Ta）double perovskite oxides: A First-Principles study

In this paper, the structural, mechanical, electronic, optical and thermodynamic properties of Ba2AsXO6 (X = V, Nb, Ta) double perovskite oxides have been studied based on the first principles of density functional theory. By calculating some parameters such as Goldsmith’s tolerance factor (tG), octahedral factor (µ), Bartel’s tolerance factor (τ), formation energy, binding energy and elastic constants, it is found that these double perovskite oxides have the potential for stable existence. In addition, Ba2AsXO6 (X = V, Nb, Ta) is an anisotropic material, in which Ba2AsVO6 is brittle, Ba2AsNbO6 and Ba2AsTaO6 are ductile. The electronic properties of the materials show that Ba2AsVO6 and Ba2AsNbO6 are indirect bandgap semiconductors with a band gap of 1.676 eV and 2.654 eV respectively, while Ba2AsTaO6 is direct bandgap semiconductor with a band gap of 3.252 eV. The optical properties revealed that these perovskites exhibit favorable far-ultraviolet light absorption characteristics. The thermodynamic properties show that the specific heat capacity of these double perovskite oxides reaches the Dulong-Petit limit at around 800 K. These results indicate that Ba2AsXO6 (X = V, Nb, Ta) double perovskite oxides have broad application prospects in the fields of thermoelectricity and optoelectronics. Furthermore, these results also provide a valuable theoretical basis for their future experimental synthesis.

Strain engineering of electronic, mechanical, and optical properties of orthorhombic III–V group monolayers by first principles calculations

Using first principles calculations, we systematically investigated the effects of strain engineering on the electronic, mechanical, and optical properties of two-dimensional (2D) orthorhombic III–V group materials, including BN, BP, BAs, AlN, AlP, and GaN. It is shown that all the III–V orthorhombic monolayers exhibit excellent mechanical anisotropy for Young’s modulus, Shear modulus, and Poisson’s ratio, especially for the AlN and GaN monolayers. AlN, AlP, and GaN are predicted to be indirect bandgap semiconductors, with their bandgap of 0.70, 0.15, and 0.53 eV, respectively. And BN is demonstrated to be a direct bandgap semiconductor (0.63 eV). Under uniaxial tensile strains, their electronic structures have non-monotonic anisotropic variations and these monolayers can be effectively modulated from metal to semiconductor, experiencing indirect–direct bandgap transitions. In addition, all the orthorhombic III–V materials exhibit highly anisotropic light-harvesting performances and the optical absorbance can be efficiently tailored with tensile strains applied along a- and b-directions. The strong optical absorptions in the visible light regions suggested that AlN, BN, and GaN may be optically tunable 2D materials for component absorbance layers for solar cell applications. The excellent anisotropic and tunable electronic, mechanical, and optical performances indicate that the orthorhombic III–V monolayers are promising candidates for potential applications of optoelectronics and photovoltaics.

Ultrahigh tunneling magnetoresistance ratios in the sandwich-structured full MXene Cr2NO2/Ti2CO2/Cr2NO2 van der Waals heterojunction

In this study, the structure, magnetism, energy-band, and spin-dependent electron transport properties of the Cr2NO2/Ti2CO2/Cr2NO2 magnetic tunnel junction (MTJ) were investigated using a combination of density functional theory and non-equilibrium Green’s function methods. The calculation band structures indicate that Cr2NO2 MXene is an “ideal” half-metal with a magnetic moment of 5.00 μB. Ti2CO2 MXene is an indirect band-gap semiconductor, and the Cr2NO2/Ti2CO2-stacked heterojunction reserve 100 % spin polarization because of the weak Van der Waals interface interaction. For the equilibrium state of the most stable Cr2NO2/Ti2CO2/Cr2NO2 MTJ, the total transmission coefficient for parallel configuration is about eleven orders of magnitude larger than that for anti-parallel configuration. An ultrahigh tunneling magnetoresistance (TMR) ratio of 1.92×1013% can be detected. For the non-equilibrium state, our calculation results show that the Cr2NO2/Ti2CO2/Cr2NO2 MTJ has a good transport performance when bias voltage ranges from 0 V to 0.1 V. The minimum TMR ratio of 7.51×1012% is detected at the bias voltage of 0.09 V, which can be considered as an excellent TMR ratio. Therefore, the Cr2NO2/Ti2CO2/Cr2NO2 MTJ is an excellent candidate for spintronic device application.

Theoretical Study of the Ternary Compound Monolayer CuP2Se for Photocatalytic Water Splitting with Efficient Optical Absorption.

Utilizing photocatalytic method to produce hydrogen by splitting water is an efficient strategy to solve the hotspot issues of energy crisis and environmental pollution. Herein, we systematically investigate the corresponding properties of the reported Cu-bearing ternary compound monolayer CuP2Se by using the first-principle calculations. The monolayer CuP2Se has quite small cleavage energy of 0.51 J/m2, indicating it can be easily produced by the mechanical exfoliation method experimentally. In addition, it is an indirect bandgap semiconductor material which has a moderate value of 1.91 eV. The conduction band minimum (CBM) and valence band maximum (VBM) can perfectly straddle the redox potentials of water when a biaxial strain of -4% to 4% is applied, unveiling the high photocatalytic thermodynamic stability of monolayer CuP2Se in response to the effect of solvent tension. Remarkably, the monolayer CuP2Se also demonstrates significant sunlight capturing ability in the visible region. The outstanding electronic and optical properties suggest that the monolayer CuP2Se is undoubtedly a viable material for photocatalytic water splitting.

Epitaxial growth and characterization of GaAs (111) on 4H-SiC

Epitaxial growth and characterization of GaAs (111) on 4H-SiC

A holistic understanding of optical properties in amorphous H-terminated Si-nanostructures: Combining TD-DFT with AIMD

Silicon, traditionally known as an indirect band gap semiconductor, unveils intriguing properties at the nanoscale, stemming from deviations from k-conservation rules within nanostructures. In our study, we scrutinized four hydrogenated Si 0D-nanostructures—Si10H16, Si14H20, Si18H24, and Si22H28—to unravel their dynamic stability under thermal fluctuations and optical characteristics. We initiated our exploration by employing the TD-DFT framework to generate and analyze the optical properties of these geometrically optimized nanostructures. Simultaneously, we conducted ab initio molecular dynamics simulations to examine the structural robustness and thermal stability of the four structures. Leveraging the Car-Parrinello molecular dynamics approach within the Quantum ESPRESSO open software suite, we observed temperature evolution and stability differences among the nanostructures at targeted temperatures 40 and 300 K. Our subsequent investigation delved into the Turbo-Lanczos time-dependent DFT method, unraveling the optical properties and excited-state dynamics of hydrogenated Si nanostructures. The results unveiled shifts towards higher energy absorption edges E0, accompanied by alterations in the permittivity tensor, complex refractive index, oscillator strength, and reflectivity. Notably, the analysis revealed an enlarged HOMO-LUMO gap, distinctive from bulk Si. Furthermore, our models predicted the elimination of phase-dependent E1/E2 optical transition peaks in the imaginary part of the dielectric function, and a gradual decrease in the low-frequency dielectric response with increased hydrogenation of the amorphous structures. These findings underscore the promising applications of hydrogenating Si nanostructures in diverse technological domains such as optoelectronics, memristors, sensors, and quantum computing. Their tunable optical properties, size-dependent behaviors, and compatibility with existing silicon-based devices make them particularly appealing for next-generation technologies.

Theoretical insights into the structural, electronic and gas-sensing properties of Sc-decorated black phosphorus via strain engineering

Structural and electronic properties of Sc-decorated black phosphorus (SP) and its gas sensing for NO molecule were investigated using density functional theory with the emphasis on the response to applied strain. It found that SP transformed into indirect bandgap semiconductor, and converted into a metal characteristic under strain. SP showed strong interaction with the NO with a high adsorption energy of −2.92 eV since the orbital hybridization and extensive charge transfer, and exhibited 3.3-fold sensitivity compared to black phosphorus, suggesting that SP was a potential NO sensor. Furthermore, strain engineering provided an effective route to facilitate the desorption of NO.

Na3Ge2P3: A Zintl Phase Featuring [P3Ge-GeP3] Dimers as Building Blocks.

Recently, ternary lithium phosphidotetrelates have attracted interest particularly due to their high ionic conductivities, while corresponding sodium and heavier alkali metal compounds have been less investigated. Hence, we report the synthesis and characterization of the novel ternary sodium phosphidogermanate Na3Ge2P3, which is readily accessible via ball milling of the elements and subsequent annealing. According to single crystal X-ray structure determination, Na3Ge2P3 crystallizes in the monoclinic space group P21/c (no. 14.) with unit cell parameters of a = 7.2894(6) Å, b = 14.7725(8) Å, c = 7.0528(6) Å, β = 106.331(6)° and forms an unprecedented two-dimensional polyanionic network in the b/c plane of interconnected [P3Ge-GeP3] building units. The system can also be interpreted as differently sized ring structures that interconnect and form a two-dimensional network. A comparison with related ternary compounds from the corresponding phase system as well as with the binary compound GeP shows that the polyanionic network of Na3Ge2P3 resembles an intermediate step between highly condensed cages and discrete polyanions, which highlights the structural variety of phosphidogermanates. The structure is confirmed by 23Na- and 31P-MAS NMR measurements and Raman spectroscopy. Computational investigation of the electronic structure reveals that Na3Ge2P3 is an indirect band gap semiconductor with a band gap of 2.9 eV.

First-principles quantum computational study to investigate radiation energy-dependent effect on optoelectronic properties of bismuth oxyhalides BiOX (X= I, Br)

Metal oxyhalides are potential candidates for fundamental and technological interest in pharmaceutical, biological, optical, photoluminance, sensing, energy, and photocatalyst applications. In this study, using first-principles density functional quantum computational approach, we investigate the electronic and optical properties of two members of bismuth oxyhalides, BiOX (X = I, Br). The study is mainly aimed to characterize and examine the light radiation energy-dependent optical properties of the compounds by using mBJ desnty functional with the full potential linearized augmented plane wave method. The oxyhalides show indirect bandgap semiconductor nature having bandgaps of 2.2 eV for BiOI and 3.5 eV for BiOBr. Besides, these are p-type materials owing to a large hole-like carrier density of states in the valence bands close to the Fermi level. The energy bands show considerable dispersion of particles. The increasing reflectivity at high light energy shows the potential of the materials as good reflectors in shielding screens or glasses to avoid damage from the ultraviolet radiation.

Optoelectronic properties, stability, and thermodynamic properties of 2D XSn2N4 (X = Cr, Mo, W) monolayers

Through first-principle calculations, we show innovative CrSn2N4, MoSn2N4 and WSn2N4 monolayers with high stability. The current results reveal that CrSn2N4 is a conductor-like material with metallic propensity, while MoSn2N4 and WSn2N4 are indirect bandgap semiconductors with narrow bandgaps of 0.16 eV and 0.39 eV, respectively. The mechanical characteristics of CrSn2N4, MoSn2N4, and WSn2N4 are stable, with Young's modulus and Poisson's ratio greater than those of graphene and C2F4. Besides, the thermodynamic characteristics were tested, and it was observed that the thermodynamic stability of MoSn2N4 was superior to the other two materials. The optical properties show the layered MoSn2N4 and WSn2N4 have strong light absorption and a wide absorption range, which have the potential for application in photovoltaic cells and devices. The spectral limits of the maximum efficiencies of 22 % and 14 % for MoSn2N4 and WSn2N4, respectively, are greater than those of SnO2. Thus, the three novel two-dimensional materials have potential applications in the area of photoelectric devices.

Modifying electronic and optical properties of violet phosphorus through variable fluorine coverage.

We present a comprehensive investigation of the electronic properties of fluorinated monolayer violet phosphorus using first-principles calculations. Our results reveal a strong dependence of the electronic properties on the different fluorine coverages of fluorination. As the fluorine coverage increases, monolayer violet phosphorus undergoes a significant transition from a wide direct bandgap semiconductor to a narrow indirect bandgap semiconductor. Moreover, both semi-fluorinated and fully fluorinated monolayer violet phosphorus exhibit advantageous semiconducting characteristics, with a tunable bandgap of 0.50 ~ 1.04 eV under biaxial strain ranging from -6% to 6%. Notably, the fully fluorinated monolayer violet phosphorus demonstrates a higher coefficient of light absorption within the visible range. Therefore, our findings highlight the tunability of monolayer violet phosphorus properties through the absorption of various fluorine coverages, providing valuable insights for the design and development of novel semiconductor devices based on this material.

High rectifying performance of armchair C[formula omitted]N heterojunction based on the interface between pristine and H-passivated nanoribbons

Two-dimensional polyaniline with a C3N structure is a newly fabricated layered material that is expected to have fascinating electronic, thermal, mechanical, and chemical properties. By performing first-principles calculations based on density functional theory and the nonequilibrium Green’s function, we first perform a stoichiometric study of the energy bands of armchair C3N nanoribbons (AC3NNRs) without and with H-passivation. The results show that the pristine AC3NNRs are metals, whereas the H-passivated nanoribbons are either direct or indirect band gap semiconductors with different edge configurations. Interestingly, additional transport calculations demonstrate that the AC3NNR-based heterojunction shows good rectification behavior. The average rectification ratio (RR) can reach up to 103 under voltage bias within the range from 0.2 to 0.4 V. In particular, extending the length of the scattering region in the heterojunction, which leads to a reduction in the current passing through the junction, allows the RR to be enlarged obviously. The average value of RR increases to a magnitude of the order of 104 under bias voltages in the range from 0.25 to 0.4 V, with a boosted maximum of up to 105 at 0.35 V. The findings of this work may be helpful in the design of functional nanodevices based on AC3NNRs in the future.

Regarding the structural, thermodynamic, mechanical, thermoelectric, and optoelectronic properties of anti-perovskite Mg3XN (X = As, Sb, and Bi) through a DFT approach

In this work, we comprehensively analyzed the structure, thermodynamics, mechanical, thermoelectric, and photoelectric properties of antiperovskite Mg3XN (X = As, Sb, and Bi) using first-principles calculations and semi-classical Boltzmann transport theory. Our calculations of phonon spectra and elastic constants suggest that Mg3XN (X = As, Sb, and Bi) exhibit excellent dynamic and mechanical stability, characterized as brittle materials with Vickers hardness (HV) values exceeding 10 GPa. Electronic structure analysis reveals that Mg3AsN is a direct bandgap semiconductor with a 2.25 eV gap, whereas Mg3SbN and Mg3BiN are indirect bandgap semiconductors with gaps of 1.58 eV and 1.41 eV, respectively. At room temperature, the lattice thermal conductivities (κL) for Mg3AsN, Mg3SbN, and Mg3BiN are 13.63, 9.93, and 7.26 Wm−1K−1, respectively, with ZT values of 0.32, 0.08, and 0.10 at optimal doping concentrations. At 1000 K, κL values decrease to 3.19, 2.29, and 1.65 Wm−1K−1, respectively, with ZT values reaching 2.12, 0.98, and 0.92. Our analysis of optical properties demonstrates that these materials exhibit absorbance in the visible and ultraviolet spectra, with negligible energy loss in the respective energy ranges, thereby rendering them suitable for photovoltaic applications.

New 2D penta-SiPN: A wide and indirect bandgap semiconductor

In recent years, two-dimensional (2D) pentagonal ternary monolayers have attracted much attention and emerged as a new class of materials because of their new feature and extensive applicability. Using first-principles density functional theory (DFT) calculations, we predict a new 2D pentagonal-SiPN or p-SiPN monolayer material. The new monolayer has shown to be structurally, thermodynamically, and dynamically stable. Our findings imply that p-SiPN is a wide and indirect bandgap semiconductor, with a highly tunable bandgap with applied equ-biaxial strain. This makes p-SiPN a promising candidate for futuristic optoelectronics and nanomechanics device applications.

Electronic and optical properties of two-dimensional Janus Sn0.5Ge0.5S monolayer

Janus two-dimensional (2D) materials have received widespread attention in recent years due to their out-of-plane asymmetric structures which makes them promising candidates for sustainable energy devices. In this work, using first-principles calculations, we study a novel 2D Janus monolayer Sn0.5Ge0.5S for recently synthesized SnS monolayer. We investigate structural, electronic and optical properties of this new 2D Janus material. Our results show that monolayer Sn0.5Ge0.5S is an indirect band gap semiconductor with the lowest conduction band is nearly flat around the band minimum. Atom projected band structure reveals that this flattened valley is mainly originated from orbitals of Sn atom. In addition, the inclusion of spin–orbit coupling leads to splitting of the bands, largely along Γ-Y direction. Optical absorption spectra indicate superior sunlight absorption in the visible and ultraviolet regions. Interestingly, absorption spectra of Janus monolayer Sn0.5Ge0.5S are polarization dependent owing to its anisotropic crystal structure along zigzag and armchair directions.