Direct Gap Research Articles

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

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

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

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

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.

Strained GeSn laser with multiple fins structure based on SiN stress

Among the IV group materials, Germanium (Ge) stands out due to its unique bandgap structure, which can be engineered to achieve direct bandgap emission. This has important applications in the fabrication of efficient integrated light sources using IV group materials. In this paper, a strained GeSn laser with Multiple Fins structure based on SiN stress is proposed, through the Multi-fins structure, the biaxial tensile stress of about 0.7GPa is predicted to be uniformly introduced into the GeSn material in the active region and the laser is predicted to exhibit a threshold current density of 180 kA cm−2 and an emission peak wavelength at 2429 nm. The design presented in this paper provides an effective solution for silicon-based integrated light source.

Comprehensive study on the optoelectronic properties of ZnSnP2 compound by DFT and simulation for the application in a photodetector

Abstract This article presents the density function theory (DFT) calculation of ZnSnP2 (ZTP) and its application as a photodetector. A DFT calculation has been performed to determine ZTP's optical and electronic characteristics. The direct bandgap of ZnSnP2 is found to be 1.0 eV which agrees well with the previously reported bandgap (0.95 eV). The total density of states (TDOS) of ZTP is determined to be 1.40 states/eV which is attributed to the 3p orbital of P, with minor impacts from the 3d orbital of Zn and the 5p orbital of Sn to TDOS. The real and imaginary dielectric functions and refractive indices ZTP have been determined to be 16.44 and 17.60, 4.07 and 2.92, respectively. The absorption coefficient and reflectivity of ZTP obtained from this investigation are 2.6×105 cm-1 and 57.5%, respectively. After calculating the electrionic and optical properties, ZTP-based n-CdS/p-ZnSnP2/p+-AlSb photodetector (PD) with CdS and AlSb as the window and back surface field (BSF) layers, respectively, has been computationally analyzed and optimized using solar cell capacitance simulator (SCAPS-1D). In a single heterojunction, the photocurrent, voltage, responsivity, and detectivity values have been obtained at 44.52 mA/cm2, 0.66 V, 0.73 A/W, and 6.81×1013 Jones, respectively. Insertion of a thin AlSb BSF layer improves the photocurrent, voltage, responsivity, and detectivity to 48.75 mA/cm2, 0.78 V, 0.86 A/W, and 8.22×1014 Jones, respectively. The outcomes are highly promising for the fabrication of a high performance ZTP-based PD in the future.

First‐Principle Investigation of zb‐TiGe: A Promising Narrow Bandgap Semiconductor

Using first‐principle calculations, a new compound semiconductor based on titanium (Ti) is predicted. It has been observed that Ti when alloyed with germanium (Ge) can crystallize in the zincblende symmetry, and exhibits semiconducting nature with a narrow bandgap. To test the robustness of the semiconducting nature, the structural properties and electronic band structure have been modeled using three different exchange–correlation functionals, namely, local density approximation, generalized gradient approximation, and Perdew‐Burke‐Ernzerhof for solids. With a nominal composition of 1:1, TiGe exhibits a direct bandgap of 0.58 eV at the “X” point of the Brillouin zone. From lattice dynamics, the structural stability of the compound has been established. The new semiconductor is characterized in detail for its electronic band structure, carrier effective mass, charge density distribution, and linear optical properties. Zb‐TiGe exhibits large effective mass for conduction band holes and tentatively becomes a prototype system to study heavy holes resulting in carrier condensation at the bottom of the conduction band. The linear optical properties of the TiGe are found to be suitable for photosensitive devices in the infrared region. In addition, TiGe may find application in deep‐UV and far‐UV regions because of the surface plasmon resonance at 6.4 eV.

DFT Analysis of Transition Metal (TM) Substitutions on Cu‐Based Chalcogenides: Structural, Electronic, and Thermophysical Properties for Interface Thermal Performance and Energy

ABSTRACTThe current investigation employs first‐principles DFT (density functional theory) calculations to examine the influence of transition metal replacements on the structural, thermodynamic, and thermoelectric properties of Cu‐based chalcogenides TMCu3Se4 (TM = Nb/Ta/V). The PBE‐generalized gradient approximation (GGA) model is utilized to compute the fundamental properties of Cu‐based chalcogenides under study. A thorough examination of the energy band structures indicates that these chalcogenides are semiconductor compounds with indirect energy bandgaps. We can infer from the calculated energy band structures that the bandgap values are 1.67, 1.77, and 1.05 eV for NbCu3Se4, TaCu3Se4, and VCu3Se4, respectively. The values for NbCu3Se4, TaCu3Se4, and VCu3Se4 are 0.661, 0.998, and 0.996, respectively. These values make them highly appropriate for usage in thermoelectric (TE) devices. The thermoelectric characteristics of pyrochlore oxides TMCu3Se4 (TM = Nb/Ta/V) suggest that these materials have promising potential for energy‐related applications. The analyzed thermodynamic properties demonstrate that the Cu0based chalcogenide materials TMCu3Se4 (TM = Nb/Ta/V) exhibit a notable level of thermal stability.

First principles investigations of linear and nonlinear optical, radiation shielding and thermoelectric properties of the non-centrosymmetric Ba-based chalcogenides Ba2In2X5 (X=S, Te)

We explore the structural, elastic, optoelectronic, Radiation Shielding, and thermoelectric properties of Ba2In2X5 (X = S, Te) using first-principles computations and semi-classical Boltzmann Transport equations. These materials are classified as semiconductors exhibiting band gaps of 2.0 eV and 3.0 eV for both investigated NLO compounds that have more significant direct band gaps of superior optical birefringence and second-order NLO coefficients. The bonding properties have been investigated by analyzing the electron charge density (ECD) contour of the (1 0 1) crystallographic plane. It is clear from the reflectivity spectra that both compounds have a high degree of reflectivity, which could make them useful as UV and visible light shields. From 0 to 14.0 eV, the approximated reflectivity values, R (ω), are displayed against the incident photon energy. Therefore, the reflectivity is around 30 % before E ≈ 12.0 eV and 40 % reflection at ∼13.0 eV. Phase matching is possible for both compounds detected, as shown by the birefringence computations. Furthermore, the radiation shielding properties of Ba2In2S5 and Ba2In2Te5 have been evaluated using Phy-X software, demonstrating their potential effectiveness in medical and nuclear energy applications. The thermoelectric properties display N-type nature at low temperatures when the Seebeck coefficient changes from N to P-type at higher temperature ranges. These compounds have remarkable optical and thermal properties, rendering them highly attractive materials for thermoelectric and optoelectronic devices.

Nanosized Eu3+-Doped NaY9Si6O26 Oxyapatite Phosphor: A Comprehensive Insight into Its Hydrothermal Synthesis and Structural, Morphological, Electronic, and Optical Properties.

Detailed analysis covered the optical and structural properties of Eu3+-doped NaY9Si6O26 oxyapatite phosphors, which were obtained via hydrothermal synthesis. X-ray diffraction patterns of NaY9Si6O26:xEu3+ (x = 0, 1, 5, 7, 10 mol% Eu3+) samples proved a single-phase hexagonal structure (P63/m (176) space group). Differential thermal analysis showed an exothermic peak at 995 °C attributed to the amorphous to crystalline transformation of NaY9Si6O26. Electron microscopy showed agglomerates composed of round-shaped nanoparticles ~53 nm in size. Room temperature photoluminescent emission spectra consisted of emission bands in the visible spectral region corresponding to 5D0 → 7FJ (J = 0, 1, 2, 3, 4) f-f transitions of Eu3+. Lifetime measurements showed that the Eu3+ concentration had no substantial effect on the rather long 5D0-level lifetime. The Eu3+ energy levels in the structure were determined using room-temperature excitation/emission spectra. Using the 7F1 manifold, the Nv-crystal field strength parameter was calculated to be 1442.65 cm-1. Structural, electronic, and optical properties were calculated to determine the band gap value, density of states, and index of refraction. The calculated direct band gap value was 4.665 eV (local density approximation) and 3.765 eV (general gradient approximation). Finally, the complete Judd-Ofelt analysis performed on all samples confirmed the experimental findings.

Enhancing Optoelectronic Performance of All-Inorganic Double Perovskites via Halogen Doping: Synergistic Screening Strategies and Multiscale Simulations.

Designing all-inorganic double perovskites through element mixing is a promising strategy to enhance their optoelectronic performance and structural stability. The complex interplay between multilevel structures and optoelectronic properties in element-mixed double perovskites necessitates further in-depth theoretical exploration. In this study, we employ screening strategies and multiscale simulations combining first-principles methods and device-scale continuum models to identify two novel element-mixed compounds, Rb2AgInCl3I3 and Cs2AgInCl3I3, as promising candidates for photovoltaic applications. These compounds exhibit favorable structural factors and suitable direct band gaps. Theoretical investigations using first-principles methods with the HSE06 functional reveal direct band gaps of 0.98 and 1.26 eV for Rb2AgInCl3I3 and Cs2AgInCl3I3, respectively, with corresponding optical absorption coefficients exceeding 105 cm-1 in the visible light range. Cs2AgInCl3I3 features high charge mobilities of approximately 20 cm2·V-1·s-1 and a notable single-junction spectroscopic limited maximum efficiency (SLME) of 25.54%. Further analysis using the device-scale continuum model simulated the nonradiative recombination effects on power conversion efficiency, integrating quantum-mechanically calculated optoelectronic properties. These theoretical investigations, which bridge composition engineering with multiscale simulations, provide valuable insights into screening novel, lead-free, halogen-mixed double metal perovskite optoelectronic devices, highlighting their potential for high-performance solar energy applications.

A Prediction of All-Inorganic Lead-Free Halide Perovskites for Photovoltaic Application: Rb3Mo2Br9 and Rb3Mo2Cl9.

Lead-based organic-inorganic hybrid perovskites show promise as photovoltaic materials due to their high energy conversion efficiencies. However, concerns regarding lead toxicity and the poor environmental and operational stability of the organic cationic group have limited their widespread application. To address these challenges, the design of all-inorganic lead-free halide perovskites offers potential solutions for photovoltaic applications. Here, two layered perovskite derivatives, Rb3Mo2Cl9 and Rb3Mo2Br9, are explored, and their electronic, structural, and photovoltaic properties are analyzed using advanced theoretical calculations. Rb3Mo2Br9 exhibits a suitable direct bandgap of 1.60eV, making it a promising candidate for use as a light absorber in low-cost, high-efficiency solar cells. On the other hand, Rb3Mo2Cl9 demonstrates a wide direct bandgap exceeding 1.70eV, positioning it as a viable option for use as a top cell in tandem photovoltaic systems alongside silicon. Both materials display ideal optical properties in the visible light region and hold promise as excellent inorganic lead-free perovskite alternatives.

Strain Engineering of ScYCCl2 MXene Monolayer and Intercalation of Metal-ions on MXene Surface: A DFT Study

The present work theoretically examines the influence of bi-axial strain on functionalized ScYCCl2 monolayer. The indirect to direct band gap transition on tensile conditions and the phase transition from semiconductor to metal on compressive strain have been studied. The analysis of extreme conditions of 10% compressive and 10% tensile strain through phonon and AIMD simulations underscore the kinetic and thermal stability, respectively of the monolayer under strain. These findings assure the possibility of experimental synthesis of the ScYCCl2 monolayer. After metallization, ScYCCl2 MXene is used as an anode of metal-ion (−Na, −K, −Li, −Mg) batteries as it has high theoretical storage capacity and low open circuit voltage. Work function engineering and the strain-dependent optical behavior of the ScYCCl2 monolayer have been examined. The work function of the ScYCCl2 monolayer has been raised under compressive strain and decreased under tensile strain. The Crystal Orbital Hamiltonian Population has been simulated under tensile and compressive strain to check the bond- strengths. Hence, the ScYCCl2 monolayer has the capability to alter its characteristics under strain. The improved optical characteristics recommend its applications in low-dimensional photonic devices and metallization after compressive strain recommends its energy storage applications in metal-ion batteries.

Prediction of 2D XC2N4 (X= Ti, Mo, and W) monolayers with high mobility as an encouraging candidate for photovoltaic devices

In this study, the impacts of strain and an electric field on the electronic and optical characteristics of monolayer XC2N4 (X=Ti, Mo, and W) were systematically examined using the density functional theory. The results corroborated that the dynamically, mechanically, and thermodynamically stable XC2N4 monolayers displayed semiconductor properties when the Heyd-Scuseria-Ernzerhof (HSE06) method was used. The TiC2N4 monolayer is shown to be a direct-gap semiconductor of 1.179 eV whereas the MoC2N4 and WC2N4 monolayers are indicated to have indirect bandgaps of 2.819 eV and 2.661 eV, respectively. Notably, the TiC2N4, WC2N4, and MoC2N4 monolayers possess comparatively high electron mobilities of 2776.85 cm2/V s, 1576.79 cm2/V s, and 1316.41 cm2/V s, respectively. The influence of strain on the bandgap of the MoC2N4 and WC2N4 monolayers led to a decrease in their gap, whereas in the TiC2N4 monolayer, the applied tensile strain caused an increase in the bandgap. Moreover, the compressive strain significantly caused a transition from semiconducting to metallic characteristics (zero band gap). The optical absorption spectra indicated the existence of three separate maxima for the XC2N4 (X=Ti, Mo, and W) monolayers with an extreme intensity of up to 2.0 × 105 cm−1. Interestingly, compared with pure monolayers, strained monolayers enhance the beginning of coefficient absorption in the visible range, with widespread range absorption in the ultraviolet and visible regions. Our results suggest that these monolayers can be promising options for nanoelectronic, optical and photovoltaic applications.

Rhodium‐Alloyed Beta Gallium Oxide Materials: New Type Ternary Ultra‐Wide Bandgap Semiconductors

AbstractBeta gallium oxide (β‐Ga2O3) is an ultra‐wide‐bandgap semiconductor with advantages for high‐power electronics. However, the power resistance of β‐Ga2O3‐based devices is still much lower than its material limit due to its flat band dispersion at its valence band maximum (VBM) and the difficulty for p‐type doping. Here, β‐Ga2O3‐based new type ternary ultra‐wide bandgap semiconductors: β‐(RhxGa1‐x)2O3’s alloys are reported with x up to 0.5. The energy and band‐dispersion curvature of β‐Ga2O3’s VBM are significantly enhanced via Rh‐alloying. Compared to that in β‐Ga2O3, the β‐(RhxGa1‐x)2O3’s VBMs increase more than 1.35 eV. The hole mass of β‐(Rh0.25Ga0.75)2O3 is only 52.3% of that in β‐Ga2O3. The decreased hole mass is correlated with the equal Rh─O bond along the b‐axis. Thanks to the simultaneous rise of conduction band minimums, the bandgaps of β‐(RhxGa1‐x)2O3 are still much larger than that in commercial silicon carbide. Moreover, the alloys show direct bandgaps in a wide range of x, and a direct and ultra‐wide bandgap of 4.10 eV is determined in β‐(Rh0.3125Ga0.6875)2O3. Combined with the enhanced valence energy, reduced hole mass, and ultra‐wide bandgap, the β‐(RhxGa1‐x)2O3 can be candidate semiconductors for a new generation of power electronics, ultraviolet optoelectronics, and complementary metal‐oxide‐semiconductor (CMOS) technologies.

Optical and thermoelectric properties of layer structured Ba2XS4 (X = Zr, Hf) for energy harvesting applications

The main objective of this research is to provide a comprehensive insight into the optical and thermoelectric properties of layer structured Ba2XS4(X = Zr, Hf) for energy harvesting applications using Density Functional Theory (DFT) and semiclassical Boltzmann transport theory. There is a good match between the computed lattice parameters and the available experimental data. Both compounds are thermodynamically and mechanically stable and they are soft, ductile, machinable, and elastically anisotropic. The indirect band gaps are found to be 1.03 eV for Ba2ZrS4 and 1.48 eV for Ba2HfS4. Both compounds possess a mixture of ionic and covalent bonding confirmed by charge density distribution and Mulliken bond population analysis. The maximum absorption is in the ultraviolet regions (∼13.6eV) of light spectra. The total thermal conductivity increases with temperature due to increasing trend of electronic thermal conductivity. The total thermal conductivity at 700 K along c-axis is 4.6 (6.1 W/mK) for Ba2ZrS4 (Ba2HfS4). For p-type Ba2ZrS4 (Ba2HfS4), power factor (PF) is about 7 (5.7) mW/mK2, whereas for n-type it is about 4 (3.9) mW/mK2 at 700 K along c-axis. The power factors of the studied compounds are much higher than those of the reported GeTe and SnSe which would create great interest for further study. The predicted ZT values at 700 K for p-type Ba2ZrS4 and Ba2HfS4 are 0.7 and 0.6, respectively. These values may further be improved through reduction of thermal conductivity and tuning ductility employing known suitable strategies such as alloying and nano-structuring. Finally, Ba2ZrS4 and Ba2HfS4 can be considered new eco-friendly alternatives to previously studied toxic lead-based thermoelectric materials. Their unique advantages of high thermodynamic stability, non-toxic nature and high performance make them strong candidate for sustainable energy solutions.

Zinc telluride material properties for solar cell application: Absorber layer

Over recent years, Zinc Telluride (ZnTe) has garnered significant interest from researches. This p-type semiconductors boasts a broad band gap, rendering it valuable in various optoelectronic uses like solar cells, LEDs, and laser displays. Given the growing interest in environmentally friendly energy alternatives, exploring the potential of nano-scale semiconducting materials for solar cells is particularly intriguing. ZnTe stands out due to its direct, wide, and adjustable optical band gap, along with its simple doping process, positioning it as a promising candidate for applications in photochemistry. This study aims to consolidate the research conducted by multiple investigators concerning the optical characteristics and electrical attributes of ZnTe thin films. The primary focus is on understanding how deposition methods and doping impacts these properties. The investigation reveals that the diverse doping techniques employed by different researchers have been extensively examined, demonstrating a positive influence of doping on these properties as well. Following the creation of solar cells based on ZnTe, they have emerged as viable and competitive substitutes for silicon solar cells, thanks to their economical nature and stable performance. As a result, there has been notable focus on advancing ZnTe thin film solar cell technology due to their promising capacity to serve as sustainable energy generators.

Study of structural, morphological and optical properties of flash evaporated cadmium sulphide thin films

Cadmium sulphide thin films were successfully synthesized by the flash evaporation method under vacuum, then annealed at various temperatures. X-Ray Diffraction patterns showed the formation of the hexagonal wurtzite phase. Structural properties of this most stable phase remain approximately the same at all investigated temperatures. Scanning Electronic Microscopy showed the formation of granular films. The Energy Dispersive X-ray spectra revealed the possible formation of stoichiometric compounds. The obtained UV–Vis spectra revealed that the prepared films exhibit a moderate direct band gap with high transmittance in the visible range. Detailed interpretation of the structural, optical, and optoelectronic findings revealed that annealed CdS thin films hold promising potential for the fabrication of the next generation of the modern optoelectronic devices. Cadmium sulphide thin films were successfully synthesized by the flash evaporation method under vacuum, then annealed at various temperatures. X-Ray Diffraction patterns showed the formation of the hexagonal wurtzite phase for all temperatures with almost the same structural properties. UV–vis spectra revealed that the prepared films exhibit a moderate direct band gap with high transmittance in the visible range, which reinforces the usefulness of these films for photovoltaic and photocatalytique applications. Scanning Electronic Microscopy shows the formation of granular films, while the Energy Dispersive X-ray spectra revealed the possible formation of stoichiometric compounds.

Design of spintronic devices based on adjustable half-metallicity induced by electric field in A-type antiferromagnetic bilayer NiI2

Exploring the attainment of half-metallic behavior in two-dimensional (2D) materials through external perturbations is a popular area of current research. In this work, we demonstrate, using first-principles calculations, that bilayer NiI2 (bi-NiI2) is an A-type antiferromagnetic (AFM) semiconductor with an indirect bandgap of 0.86 eV, with the most stable configuration being the AB stacking mode. Upon the application of a vertical electric field, the material transforms from its original semiconducting state into a half-metallic state. Moreover, the spin polarization reverses its orientation whenever the direction of the electric field is altered. This intriguing behavior has inspired us to design a spintronic device based on the A-type AFM bi-NiI2. By employing nonequilibrium Green's function (NEGF) combined with density functional theory (DFT) calculations, we find that the device achieves ON/OFF switching by applying vertical electric fields in parallel or anti-parallel configurations in the two leads. The device displays 100 % spin polarization in the parallel configuration (PC) scenario, driven by bias voltage or temperature differences. Utilizing either the parallel or antiparallel configuration (APC) for ON/OFF switching enables the device to exhibit tunneling magnetoresistance (TMR) of up to 1.45 × 1010 % due to bias voltage and up to 1011 % thermal TMR arising from temperature differences between the leads. These findings highlight the potential of NiI2 and A-type AFM bilayers in the design of spintronic devices.

Stimulated emission from hexagonal silicon-germanium nanowires

Hexagonal crystal phase silicon-germanium (hex-SiGe) features efficient direct bandgap emission between 1.5 and 3.4 µm. For expanding its application potential, the key challenge is to demonstrate material gain for enabling a hex-SiGe semiconductor laser. Here we report the transition from the spontaneous emission regime to the stimulated emission-dominated amplified spontaneous emission regime in the optically excited part of a hexagonal Si0.2Ge0.8 nanowire. We observe narrow resonance peaks arising above a spontaneous emission background, which show lasing signatures such as a threshold and a superlinear increase of the emission. A Hakki-Paoli analysis of the height of the cavity resonances provides the gain spectrum of hex-SiGe, showing evidence for a positive material gain. Measurements of the cavity line widths provide an independent assessment of the total cavity loss. While lasing has not been reached, the observation of optical amplification and amplified spontaneous emission provides a clear roadmap toward lasing in hexagonal SiGe. This opens a new pathway for the monolithic integration of a Si-compatible laser within electronic chips.

Strain-modulated antiferromagnetic Chern insulator in NiOsCl$_6$ monolayer

Abstract Recently, Chern insulators in an antiferromagnetic (AFM) phase have been suggested theoretically and predicted in a few materials. However, the experimental observation of two-dimensional AFM quantum anomalous Hall effect is still a challenge to date. In this work, we propose that an AFM Chern insulator can be realized in a two-dimensional monolayer of NiOsCl$_6$ modulated by a compressive strain. Strain modulation is accessible experimentally and used widely in predicting and tuning topological nontrivial phases. With first-principles calculations, we have investigated the structural, magnetic and electronic properties of NiOsCl$_6$. Its stability has been confirmed through molecular dynamical simulations, elasticity constant and phonon spectrum. It has a collinear AFM order, with opposite magnetic moments of 1.3 $\mu_B$ on each Ni/Os atom, respectively, and the Néel temperature is estimated to be 93 $K$. In the absence of strain, it functions as an AFM insulator with a direct gap with spin-orbital coupling included. Compressive strain will induce a transition from a normal insulator to a Chern insulator characterized by a Chern number $C = 1$, with a band gap of about 30 meV. This transition is accompanied by a structural distortion. Remarkably, the Chern insulator phase persists within the 3$\%$-10$\%$ compressive strain range, offering an alternative platform for the utilization of AFM materials in spintronic devices.