Indirect Gap Semiconductor Research Articles

First-principles study of oxygen vacancy defects in β-quartz SiO2/Si interfaces

Abstract Understanding the electronic structures of gate oxides in Si-based devices is significant for improving device performance. We investigate the electronic properties of the oxygen vacancy defects in β-quartz SiO2/Si interface structure using first-principles calculations. The results indicate that the constructed (SiO2)4/(Si)4 structure is an indirect-gap semiconductor, with its band edges contributed by Si side and a large band-edge energy difference ( > 1.780 eV). Our study reveals that the presence of oxygen vacancy defects reduces the band gap, and V O 1 is transformed from indirect into direct band gap. The Si dangling bonds in V O 1 cause charge localization around the O vacancy, while the formation of Si–Si bonds in V O 2 and V O 3 lead to electron delocalization. In the calculation of defect formation energies, we find that V O 1 maintains the lowest formation energy across different states, making it more likely to form and structurally stable. Compared to O-rich environments, the formation energy in O-poor environments is overall reduced by approximately 4.5 eV, indicating that oxygen vacancy defects are more likely to form and be controlled under O-poor conditions. Our study emphasizes the importance of interface structure and defect characteristics in semiconductor research, providing insights for the development of Si-based devices.

Two-photon absorption in silicon using the real density matrix approach.

Two-photon absorption in indirect gap semiconductors is a frequently encountered, but not well-understood phenomenon. To address this, the real-density matrix approach is applied to describe two-photon absorption in silicon through the excitonic response to the interacting fields. This approach produces an analytical expression for the dispersion of the two-photon absorption coefficient for indirect-gap materials and can be used to explain trends in reported experimental data for bulk silicon both old and new with minimal fitting.

Electronic and magnetic properties of Janus ZrSSe monolayer doped with V impurity and VX3(X = C, N, O, and F) clusters

In this work, doping with V impurity and VX3 (X = C, N, O, and F) clusters is proposed to modify the electronic and magnetic properties of Janus ZrSSe monolayer. Pristine ZrSSe monolayer is an indirect-gap semiconductor two-dimensional (2D) material with energy gap of 0.73 eV. This value is reduced to 0.13 eV under effects of single Zr vacancy, which corresponds to the reduction of the order of 82.19%. V impurity magnetizes significantly ZrSSe monolayer, inducing feature-rich magnetic semiconductor nature. Herein, the magnetism with a total magnetic moment of 1.00 μ B is produced mainly by V-3d orbital. Investigations indicate that the antiferromagnetic state with zero total magnetic moment is stable when V impurities are located close to each other. Further separating impurities causes the antiferromagnetic-to-ferromagnetic state transition, such that a total magnetic moment of 2.00 μ B is obtained. ZrSSe monolayer is metallized by doping with VC3, VN3 and VF3 clusters. In the first two cases, the non-magnetic nature is preserved. Meanwhile, significant magnetization with a total magnetic moment of 3.00 μ B is achieved by VF3 cluster substitution. Similarly, VO3 cluster induces significant magnetic properties in ZrSSe monolayer with a total magnetic moment of 1.00 μ B , which are originated mainly from the antiparallel spin orientation between V atom and Se atoms closest to the doping sites. Herein, VO3 cluster substitution in ZrSSe monolayer makes new magnetic semiconductor 2D material. The Bader charge analysis indicates that all four clusters attract charge from the host monolayer. Our work may introduce efficient approaches to modify the ZrSSe monolayer electronic and magnetic properties towards spintronic and optoelectronics applications.

[formula omitted] magnetism engineering in the low-buckled hexagonal SiS monolayer: A first-principles study

In this work, vacancy- and doped-induced magnetism engineering is investigated to functionalize the non-magnetic low-buckled hexagonal silicon sulfide (SiS) monolayer. This monolayer is an indirect gap semiconductor two-dimensional (2D) material with an energy gap of 2.20(3.02) eV obtained from the PBE(HSE06)-based calculations. Creating a single Si vacancy leads to a significant magnetization of SiS monolayer with the feature-rich half-metallic nature. Herein, a total magnetic moment of 1.89 μB is obtained and magnetic properties are produced mainly by S and Si atoms closest to the defect site. In contrast, single S vacancy preserves the non-magnetic nature inducing a band gap reduction of the order of 26.36%. n-type doping with P atom metalizes the monolayer, meanwhile As impurity leads to the emergence of the half-metallicity with a total magnetic moment of 1.00 μB. Similarly, this value is also obtained by p-doping using P and As atoms as dopants, where the diluted magnetic semiconductor nature is obtained. Moreover, doping with IA- (Na and K) and IIIA-group (Al and Ga) atoms is also proposed to engineer the magnetism in SiS monolayer. It is found that these impurities induce either half-metallic or diluted magnetic semiconductor behaviors with total magnetic moment between 0.99 and 1.00 μB. The electronic and magnetic properties are regulated mainly by the interactions between impurities and their neighbor S atoms, which modify the charge distribution in their outermost orbitals. In addition, the Bader charge analysis asserts that dopant atoms gain charge from the host monolayer when substituting S atom, meanwhile they act as charge loser — transferring charge to the host monolayer when doping at Si sublattice. The presented results may suggest efficient approaches to properly engineer SiS monolayer electronic and magnetic properties, making new 2D candidates for spintronic applications.

First-Principles Study of Penta-PtXY (X = Se, Te; Y = S, Te; X ≠ Y) Monolayer with Highly Anisotropic Electronic and Optical Properties.

Two-dimensional (2D) semiconducting materials with anisotropic physical properties have induced lively interest due to their application in the field of polarizing devices. Herein, we have designed a family of penta-PtXY (X = Se, Te; Y = S, Te; X ≠ Y) monolayers and predicted the electronic and optical properties based on the first-principles calculation. The results suggest that the penta-PtXY (X = Se, Te; Y = S, Te; X ≠ Y) monolayers are indirect-gap semiconductors with a medium bandgap of 2.29-2.66 eV. The penta-PtXY (X = Se, Te; Y = S, Te; X ≠ Y) monolayers own a remarkable mechanical anisotropy with a high Young's modulus anisotropic ratio (3.0). In addition, the penta-PtXY (X = Se, Te; Y = S, Te; X ≠ Y) monolayers exhibit a high anisotropy ratio of hole/electron mobility in the x and y directions (1.16-3.54). The results calculated by the G0W0+BSE method indicate that the single-layers also bear a salient optical anisotropy ratio (1.56-2.11). The integration of the anisotropic electronic, optical, and mechanical properties entitles penta-PtXY (X = Se, Te; Y = S, Te; X ≠ Y) monolayers as potential candidates in multifunctional polarized nanodevices.

Synthesis, crystal structure of Ca6Sb2O11 from experiments and DFT-electron structure calculation

This article reports a new perovskite compound Ca6Sb2O11. The X-ray powder diffraction technique was used to analyze its crystal structure. The results show that Ca6Sb2O11 has a tetragonal structure with the I4/m space group, and the lattice parameters are a = b = 5.658 (1) Å, c = 7.984 (1) Å, α = β = γ = 90°. It exhibits a typical A4B'2B″2X12-x anoxic multi-perovskite structure with rock-salt ordering of the B-site cations. The compound's chemical composition and valence states were characterized through scanning electron microscopy-energy dispersion spectrum (SEM-EDS) and X-ray photoelectron spectroscopy (XPS). The presence of oxygen vacancies was confirmed by electron paramagnetic resonance (EPR) spectroscopy. A chemical and structure transition temperature and the full melting temperature of Ca6Sb2O11 were measured, with values of 1515 ± 3 K and 1720 ± 3 K, respectively. The density functional theory (DFT)-electron structure calculation results show that Ca6Sb2O11 is an indirect wide-band gap (∼4.47 eV) semiconductor material, which agrees well with the experimental value (∼4.38 eV) obtained through diffuse reflection spectroscopy (DRS). Moreover, the top of the valence band and bottom of the conduction band are mainly contributed to by O-2p and Ca-3d states, respectively.

Searching for new two-dimensional spintronic materials: Doping-induced magnetism in graphene-like SrS monolayer

In this work, doping approach is explored to induce feature-rich electronic and magnetic properties in graphene-like SrS monolayer and make it prospective spintronic two-dimensional (2D) candidate. For such goal, 3d transition metals (V, Cr, Mn, and Fe) and halogens (F, Cl, Br, and I) are selected as dopants at Sr and S sublattice, respectively. Pristine SrS single layer shows good dynamical and thermal stability. Its indirect-gap semiconductor nature is also asserted with energy gap of 2.87/3.81 eV obtained by PBE/HSE06 functional, generated by the separation in energy between S-3p and Sr-4d orbitals. The magnetic semiconducting with total magnetic moment of 2.00 μB is obtained by creating a single Sr vacancy, meanwhile S single vacancy preserves the non-magnetic nature. The monolayer is significantly magnetized by doping with transition metals, where large total magnetic moments of 3.00, 4.00, and 5.00 μB are obtained for the V-, Cr/Fe-, and Mn-doped SrS monolayer, respectively. In these cases, impurities play a key role on producing magnetic properties and generating the magnetic semiconductor nature. This feature-rich nature is also induced by doping with F atom, where a total magnetic moment of 1.00 μB is obtained that is originated mainly from Sr atoms closest to the doping site. Besides, Cl doping leads to the emergence of the half-metallicity. Importantly, the magnetization becomes significantly weaker according to increase the atomic number of halogen dopants, such that the non-magnetic nature is preserved by doping with I atom. This feature is attributed to the increase of the electronic hybridization. Results presented herein introduce the doped SrS monolayer as promising 2D spintronic materials, exhibiting novel properties that are not found in the pristine counterpart.

Exploration of new Janus GeBrI monolayer for optoelectronic and spintronic applications

Two-dimensional (2D) materials have been explored for diverse applications, where multifunctional candidates with two or more functions are desired. In this work, new Janus GeBrI monolayer with interesting electronic and magnetic properties is investigated. Standard PBE and hybrid HSE06 functionals assert the indirect gap semiconductor behavior of pristine monolayer with band gap of 2.28 and 3.04 eV, respectively. Novel feature-rich properties can be induced in Janus GeBrI monolayer by defect engineering and doping. Specifically, single Ge vacancy (VGe) metalizes the monolayer without magnetism. Similarly, the non-magnetic nature is kept by doping with IIA-group (Be and Mg: BeGe and MgGe) atoms, where the energy gap exhibits a slight increase of the order between 1.32% and 3.51%. In contrast, this 2D material is significantly magnetized by single halogen vacancy (VBr and VI), doping with IIIA-group (Al and Ga: AlGe and GaGe) atoms, and doping with chalcogen (Se and Te: SeBr, SeI, TeBr, and TeI) atoms. In these cases, total magnetic moments between 0.61 and 1.00 μB are obtained, where impurities and those atoms closest to the defect/doping site originate mainly the system magnetism. Moreover, VBr, VI, AlGe, GaGe systems exhibit the diluted magnetic semiconductor nature, while SeBr, SeI, TeBr, and TeI systems are classified as 2D half-metallic structures. Further, Bader charge analysis indicates the charge loser of IIIA- and IIA-group impurities when transferring charge to the host monolayer. Meanwhile, chalcogen dopants are charge gainers attracting charge from the host monolayer. The presented results introduce new stable Janus GeBrI monolayer with relative large intrinsic band gap, further functionalization processes based on the vacancy defects and doping of this 2D material may make prospective 2D spintronic materials.

Engineering the half-metallic and magnetic semiconductor natures in gallium phosphide monolayer towards spintronic applications

In this work, magnetism engineering in the Gallium phosphide (GaP) monolayer is explored in order to create new two-dimensional (2D) spintronic materials. Pristine monolayer is a non-magnetic indirect gap semiconductor with band gap of 1.61(2.49) eV obtained from the PBE(HSE06)-based calculations. Both ionic and covalent characters form the Ga-P chemical bond, which are generated by the charge transfer and electronic hybridization, respectively. It is found that creating a single Ga vacancy magnetizes significantly GaP monolayer (VGa), where a large total magnetic moment of 2.88 μB is obtained and magnetic properties are produced mainly by P atoms around the defect site. Meanwhile, GaP monolayer is metallized under effects of single P vacancy, where the non-magnetic nature is preserved. Significant magnetization is also achieved by doping with alkali (Li and Na - LiGa and NaGa) and alkaline earth (Be and Mg - BeGa and MgGa) metals. In these cases, total magnetic moments of 2.00 and 1.00 μB are obtained, respectively. Besides, doping with S (SP) and Se (SeP) atoms induces weaker magnetization, which is reflected in smaller total magnetic moments of 0.60 and 0.96 μB, respectively. Interestingly, the half-metallicity is observed in VGa, BeGa, and MgGa systems; while LiGa, NaGa, and SeP systems exhibit the diluted magnetic semiconductor behavior. In contrast, Cl (ClP) and Br (BrP) impurities induces no magnetism in GaP monolayer. However both ClP and BrP systems have energy gap of 0.76 eV, which corresponds to a reduction of the order of 52.80% from that of pristine monolayer. Results presented herein may introduce efficient methods to modify the GaP monolayer electronic and magnetic properties, such that new multifunctional 2D materials can be created for spintronic and optoelectronic applications.

Watt-level continuous-wave antimonide laser diodes with high carrier-confined active region above 2.5 µm

Thanks to high performance above room temperature, antimonide laser diodes have shown great potential for broad application in the mid-infrared spectral region. However, the laser`s performance noticeably deteriorates due to the reduction of carrier confinement with increased emission wavelength. In this paper, a novel active region with higher carrier confinements both of electron and hole, by the usage of an indirect bandgap material of Al0.5GaAs0.04Sb as the quantum barrier, was put up to address the poor carrier confinement of GaSb-based type-I multi-quantum-well (MQW) diode lasers emission wavelength above 2.5 µm. The carrier confinement and the differential gain in the designed active region are enhanced as a result of the first proposed usage of an indirect-gap semiconductor as the quantum barrier with larger band offsets in conduction and valence bands, leading to high internal quantum efficiency and low threshold current density of our lasers. More importantly, the watt-level output optical power is obtained at a low injection current compared to the state of the art. Our work demonstrates a direct and cost-effective solution to address the poor carrier confinement of the GaSb-based MQW lasers, thereby achieving high-power mid-infrared lasers.

Bi-based bracelet-like monolayer with negative in-plane Poisson’s ratio and enhanced photocatalytic performance: a first-principles study

Auxetic materials are in high demand for advanced applications due to their relatively rare negative Poisson’s ratio in two-dimensional materials. This study investigates the structural, mechanical, electronic, optical and photocatalytic properties of the AsBiTe3 monolayer(ML) using first-principles calculations. Through analysis of phonon dispersion curves, ab-initio molecular dynamics simulations, and Born conditions, we have confirmed the thermal, dynamic, and mechanical stability of the AsBiTe3 monolayer. The study of the mechanical properties of this material revealed significant anisotropy and a bidirectional in-plane negative Poisson’s ratio (NPR). In addition, electronic band structures calculated, with and without spin–orbit coupling (SOC) using the HSE functional, indicate that this monolayer exhibits the characteristics of an indirect-gap semiconductor around 1.17 and 1.32 eV, respectively. Notably, by assessing the optical properties of AsBiTe3 monolayer, it has been found that this monolayer has a strong light-harvesting capability with an absorption coefficient higher than 105 cm −1 in the visible region. Fascinatingly, under a biaxial 1 % and 4 % tensile and −2% compressive strain, the band edge of the AsBiTe3 monolayer extends across the redox potential of water at pH = 0, 7 and 14, respectively. This suggests that this monolayer holds promise as a potential material for catalytic water splitting. These results should inspire further experimental and theoretical research, aimed at fully exploring the potential applications of this new class of 2D materials.

Realizing new 2D spintronic materials from the non-magnetic 1T-PdO2 monolayer through vacancy defects and doping.

In this work, vacancy- and doping-based magnetism engineering in a non-magnetic 1T-PdO2 monolayer is explored in order to realize new two-dimensional (2D) spintronic materials. The pristine monolayer is an indirect gap semiconductor with a band gap of 1.45 (3.20) eV obtained using the PBE (HSE06) functional. Half-metallicity with a total magnetic moment of 3.95 μB is induced by creating a single Pd vacancy, where the magnetic properties are produced mainly by O atoms around the vacancy site. In contrast, the non-magnetic nature is preserved under the effects of a single O vacancy, however a band gap reduction in the order of 37.93% is achieved. Further doping with transition metals (TMs = V, Cr, Mn, and Fe) in the Pd sublattice and with non-metals (B, C, N, and F) in the O sublattice is investigated. TM impurities lead to the emergence of a diluted magnetic semiconductor nature, where total magnetic moments of 1.00, 2.00, and 3.00 μB are obtained in the V-, Cr(Fe)-, and Mn-doped systems, respectively. In these cases, the TMs' 3d electrons mainly originate the system's magnetism. Significant magnetization of the PdO2 monolayer is also achieved by doping with B, N, and F atoms, where either half-metallic or diluted magnetic semiconductor natures are induced. Herein, electronic and magnetic properties are regulated mainly by the interactions between the 2p orbital of the dopant, 4d orbital of the first neighbor Pd atoms, and 2p orbital of the second neighbor O atoms. Meanwhile, C impurity induces no magnetism in the PdO2 monolayer because of the strong electronic hybridization with their neighbor atoms. Results presented herein may introduce efficient approaches to engineer magnetism in a non-magnetic PdO2 monolayer, such that the functionalized systems are further recommended for prospective spintronic applications.

Electronic and magnetic properties of GeS monolayer effected by point defects and doping.

In this work, defect engineering and doping are proposed to effectively functionalize a germanium sulfide (GeS) mononolayer. With a buckled hexagonal structure, the good dynamical and thermal stability of the GeS monolayer is confirmed. PBE(HSE06)-based calculations assert the indirect gap semiconductor nature of this two-dimensional (2D) material with a relatively large band gap of 2.48(3.28) eV. The creation of a single Ge vacancy magnetizes the monolayer with a total magnetic moment of 1.99 μB, creating a the feature-rich half-metallic nature. VaS vacancy, VaGeS divacancy, SGe and GeS antisites preserve the non-magnetic nature; however, they induce considerable band gap reduction of the order 47.98%, 89.11%, 29.84%, and 62.5%, respectively. By doping with transition metals (TMs), large total magnetic moments of 3.00, 4.00, and 5.00 μB are obtained with V, Cr-Fe, and Mn impurities, respectively. The 3d orbital of TM dopants mainly regulates the electronic and magnetic properties, which induces either the half-metallic or diluted magnetic semiconductor nature. It is found that the doping site plays a determinant role in the case of doping with VA-group atoms (P and As). The GeS monolayer can be metallized by doping the Ge sublattice, meanwhile both spin states exhibit semiconductor character with strong spin polarization upon doping the S sublattice to obtain a diluted magnetic semiconductor nature with a total magnetic moment of 1.00 μB. In these cases, the magnetism originates mainly from P and As impurities. The obtained results suggest an efficient approach to functionalize the GeS monolayer for optoelectronic and spintronic applications.

Controlling the electronic and magnetic properties of the GeAs monolayer by generating Ge vacancies and doping with transition-metal atoms.

Controlling the electronic and magnetic properties of two-dimensional (2D) materials is a key step to make new multifunctional candidates for practical applications. In this work, defects and doping with transition metals (TMs = V, Cr, Mn, and Fe) at Ge sublattices are proposed in order to develop novel features in the hexagonal germanium arsenide (GeAs) monolayer. The pristine GeAs monolayer is a non-magnetic indirect gap semiconductor with an energy gap of 1.20(1.82) eV as provided by PBE(HSE06)-based calculations. A single Ge vacancy metallizes the monolayer, preserving its non-magnetic nature. In contrast, significant magnetization with a total magnetic moment of 1.96 μ B is achieved by a pair of Ge vacancies. Herein, the computed band structures assert the half-metallic behavior of the defective system. Similarly, half-metallicity is also obtained by V, Mn, and Fe doping. Meanwhile, the Cr-doped GeAs monolayer is classified as a diluted magnetic semiconductor 2D system. In these cases, magnetic properties are produced mainly by TM-3d electrons with total magnetic moments between 2.00 and 4.00 μ B. Further, the effects of substituting a pair of Ge atoms with a pair of TM atoms (pTMGe systems) are also investigated. Results indicate the ferromagnetic half-metallicity of the pVGe system, meanwhile antiferromagnetic ordering is stable in the remaining cases. In all cases, TM impurities transfer charge to the host GeAs monolayer since they are surrounded by As atoms, which are more electronegative than dopant atoms. Results presented herein may introduce new 2D systems - made from the non-magnetic GeAs monolayer - for spintronic applications with suitable electronic and magnetic features controlled mainly by transition metals.

Modifying the electronic and magnetic properties of the scandium nitride semiconductor monolayer via vacancies and doping.

In this work, the effects of vacancies and doping on the electronic and magnetic properties of the stable scandium nitride (ScN) monolayer are investigated using first-principles calculations. The pristine monolayer is a two-dimensional (2D) indirect-gap semiconductor material with an energy gap of 1.59(2.84) eV as calculated using the GGA-PBE (HSE06) functional. The projected density of states, charge distribution, and electron localization function assert its ionic character generated by the charge transfer from the Sc atoms to the N atoms. The monolayer is magnetized by a single Sc vacancy with a total magnetic moment of 3.00μB, while a single N vacancy causes a weaker magnetization with a total magnetic moment of 0.52μB. In both cases, the magnetism originates mainly from the atoms closest to the defect site. Significant magnetization is also reached by doping with acceptor impurities. Specifically, a total magnetic moment of 2.00μB is obtained by doping with alkali metals (Li and Na) in the Sc sublattice and with B in the N sublattice. Doping with alkaline earth metals (Be and Mg) in the Sc sublattice and with C in the N sublattice induces a value of 1.00μB. In these cases, either magnetic semiconducting or half-metallicity characteristics arise in the ScN monolayer, making it a prospective 2D spintronic material. In contrast, no magnetism is induced by doping with donor impurities (O and F atoms) in the N sublattice. An O impurity metallizes the monolayer; meanwhile, F doping leads to a large band-gap reduction of the order of 82%, widening the working regime of the monolayer in optoelectronic devices. The results presented herein may introduce efficient methods to functionalize the ScN monolayer for optoelectronic and spintronic applications.

Metal Sulfide Ion Exchangers: High Acid Stability of Na2xMg2y-xSn4-yS8 (NMS) and Topotactic Conversion to 2D Solid Acids with Semiconducting Character.

Metal sulfide ion exchange materials (MSIEs) are of interest for nuclear waste remediation applications. We report the high stability of two structurally related metal sulfide ion exchange materials, Na2xMg2y-xSn4-yS8 (Mg-NMS) and Na2SnS3 (Na-NMS), in strongly acid media, in addition to the preparation of Na2xNi2y-xSn4-yS8 (Ni-NMS). Their formation progress during synthesis is studied with in-situ methods, with the target phases appearing in <15 min, reaction completion in <12 h, and high yields (75-80%). Upon contact with nitric or hydrochloric acid, these materials topotactically exchange Na+ for H+, proceeding in a stepwise protonation pathway for Na5.33Sn2.67S8. Na-NMS is stable in 2 M HNO3 and Mg-NMS is stable in 4 M HNO3 for up to 4 h, while both NMS materials are stable in 6 M HCl for up to 4 days. However, the treatment of Mg-NMS and Na-NMS with 2-6 M H2SO4 reveals a much slower protonation process since after 4 h of contact both NMS and HMS are present in the solution. The resultant protonated materials, H2xMg2y-xSn4-yS8 and H4x[(HyNay-1)1.33xSn4--1.33x]S8, are themselves solid acids and readily react with and intercalate a variety of organic amines, where the band gap of the resultant adduct is influenced by amine choice and can be tuned within the range of 1.88(5)-2.27(5) eV. The work function energy values for all materials were extracted from photoemission yield spectroscopy in air (PYSA) measurements and range from 5.47 (2) to 5.76 (2) eV, and the relative band alignments of the materials are discussed. DFT calculations suggest that the electronic structure of Na2MgSn3S8 and H2MgSn3S8 makes them indirect gap semiconductors with multi-valley band edges, with carriers confined to the [MgSn3S8]2- layers. Light electron effective masses indicate high electron mobilities.

Point Defects in Buckled Honeycomb PAs Monolayer: A Systematic Study of Stability, Electronic, and Magnetic Properties

AbstractIn this work, the effects of point defects on the electronic and magnetic properties of PAs monolayer are investigated. PAs monolayer is stable in a buckled hexagonal structure, exhibiting indirect gap semiconductor character and is metallized under the presence of vacancies due to the dangling bonds around defect sites. Meanwhile, the non‐magnetic semiconductor character is preserved upon creating antisite defects with a negligible variation of the band gap. Significant magnetism as well as feature‐rich electronic properties are induced by p‐ and n‐type defects. Specifically, doping with Si and Ge atoms leads to the emergence of the magnetic semiconductor nature. In these cases, the total magnetic moment of 1 is obtained, where dopant atoms are mainly responsible for the magnetization. Besides, doping with Br induce the half‐metallic nature with a total magnetic moment of 2 , where magnetic properties are produced by the dopant and its neighbor due to the strong hybridization. In contrast, weak hybridization is the main reason for the absence of magnetism in the Cl‐doped PAs monolayer. Results presented herein introduce the creation of point defects in buckled semiconductor PAs monolayer as efficient functionalization approaches for optoelectronic and spintronic applications.

Phonon-Assisted Auger-Meitner Recombination in Silicon from First Principles.

We present a consistent first-principles methodology to study both direct and phonon-assisted Auger-Meitner recombination (AMR) in indirect-gap semiconductors that we apply to investigate the microscopic origin of AMR processes in silicon. Our results are in excellent agreement with experimental measurements and show that phonon-assisted contributions dominate the recombination rate in both n-type and p-type silicon, demonstrating the critical role of phonons in enabling AMR. We also decompose the overall rates into contributions from specific phonons and electronic valleys to further elucidate the microscopic origins of AMR. Our results highlight potential pathways to modify the AMR rate in silicon via strain engineering.

Thermoelectric response of Janus monolayer M2P2S3Se3 (M = Zn and Cd).

Thermoelectric transport properties of Janus monolayers M2P2S3Se3 (M = Zn and Cd) are investigated by the first-principles based transport theory. The Zn2P2S3Se3 and Cd2P2S3Se3 monolayers are indirect-gap semiconductors. The high polarizability of M-Se/S bonds in the MS3Se3 distorted octahedrons leads to anharmonic phonon behavior, which produces an intrinsic lattice thermal conductivity (κl) as low as 1.06 and 1.99W m-1 K-1 at 300K for Zn2P2S3Se3 and Cd2P2S3Se3 monolayers, respectively. The lower κl of the Zn2P2S3Se3 monolayer is mainly attributed to more pronounced flat modes of the phonon dispersion in a frequency range of 1-1.7THz caused by the softer Zn-Se/S bonds. The polar optical phonon scattering of carriers surprisingly plays a dominant role in carrier transport of both the monolayers, which greatly suppresses the electrical conductivity and thereby the power factor by about an order of magnitude. The predicted figure of merit (zT) increases monotonically with the temperature at the optimal carrier density, and at the operating temperature of 1200K, it reaches an optimal value of 0.86 at an optimal electron density of ∼1.5×1013 cm-2 for the n-type Zn2P2S3Se3 monolayer and 0.30 at an optimal electron density of ∼7×1012 cm-2 for the n-type Cd2P2S3Se3 monolayer.

Composition-Defined Optical Properties and the Direct-to-Indirect Transition in Core-Shell In1-xGaxP/ZnS Colloidal Quantum Dots.

Semiconductors are commonly divided into materials with direct or indirect band gaps based on the relative positions of the top of the valence band and the bottom of the conduction band in crystal momentum (k) space. It has, however, been debated if k is a useful quantum number to describe the band structure in quantum-confined nanocrystalline systems, which blur the distinction between direct and indirect gap semiconductors. In bulk III-V semiconductor alloys like In1-xGaxP, the band structure can be tuned continuously from the direct- to indirect-gap by changing the value of x. The effect of strong quantum confinement on the direct-to-indirect transition in this system has yet to be established because high-quality colloidal nanocrystal samples have remained inaccessible. Herein, we report one of the first systematic studies of ternary III-V nanocrystals by utilizing an optimized molten-salt In-to-Ga cation exchange protocol to yield bright In1-xGaxP/ZnS core-shell particles with photoluminescence quantum yields exceeding 80%. We performed two-dimensional solid-state NMR studies to assess the alloy homogeneity and the extent of surface oxidation in In1-xGaxP cores. The radiative decay lifetime for In1-xGaxP/ZnS monotonically increases with higher gallium content. Transient absorption studies on In1-xGaxP/ZnS nanocrystals demonstrate signatures of direct- and indirect-like behavior based on the presence or absence, respectively, of excitonic bleach features. Atomistic electronic structure calculations based on the semi-empirical pseudopotential model are used to calculate absorption spectra and radiative lifetimes and evaluate band-edge degeneracy; the resulting calculated electronic properties are consistent with experimental observations. By studying photoluminescence characteristics at elevated temperatures, we demonstrate that a reduced lattice mismatch at the III-V/II-VI core-shell interface can enhance the thermal stability of emission. These insights establish cation exchange in molten inorganic salts as a viable synthetic route to nontoxic, high-quality In1-xGaxP/ZnS QD emitters with desirable optoelectronic properties.