Direct Gap Research Articles

Continuous-Flow Synthesis of Zn1-xMnxS Nanoparticles at Ambient Conditions.

With its large direct band gap and good chemical stability, ZnS is suitable for many applications, including light-emitting diodes, panel displays, and photodetection. Here, nanoparticles of ZnS are synthesized phase pure under ambient conditions by precipitation in a simple and scalable continuous-flow reactor. Furthermore, different degrees of Zn substitution with Mn have been investigated, Zn1-xMnxS, with x = 0.05, 0.19, and 0.25 according to X-ray fluorescence measurements. The products are analyzed with multitemperature synchrotron powder X-ray diffraction (PXRD) and X-ray total scattering. The analysis reveals phase-pure synthesis products with the sphalerite structure and crystallite sizes in the range of 3.8-4.7 nm in agreement with scanning transmission electron microscopy. Only Zn0.75Mn0.25S shows traces of Mn3O4, indicating that x = 0.25 is above the substitution limit as the impurity appears. Substitution of Zn with Mn in the nanoparticles is confirmed by energy-dispersive X-ray spectroscopy, as well as an observed decrease in the band gap, decrease in the sphalerite-to-wurtzite phase transition temperature, and increase in the unit cell dimensions with increasing Mn content. Based on the modeling of the PXRD Rietveld refined atomic displacement parameters, the Debye temperature for ZnS and Zn0.95Mn0.05S is determined to be 322 ± 13 and 394 ± 22 K, respectively.

Theoretical insight into physical characteristics of lead-free perovskites Rb2TlSbX6 (X = Cl, Br, I) for optoelectronic devices.

Novel optoelectronic and thermoelectric properties with broad compositional range, non-toxic nature and structural stability make halide-based double perovskites fascinating for flexible optoelectronic devices. In this work, the structural electronic, optical and transport properties of Rb2TlSbX6 (X = Cl, Br, I) were studied using density functional theory for optoelectronic devices. The elastic analysis demonstrates ductile nature, mechanical stability, anisotropic behaviour and feasibility for flexible optoelectronic devices. The band structure study using Tran-Blaha-modified Becke-Johnson (TB-mBJ) potential shows that all studied materials have direct bandgap. In addition, the bandgap of Rb2TlSbCl6 is more appropriate for optoelectronic devices. The small loss and maximum absorption in visible regions make these materials prime candidates for optoelectronic devices. The transport features indicate that all the studied double perovskites reflect p-type semiconducting behaviour as highlighted by positive Seebeck coefficient values. Furthermore, the high power factor values of Rb2TlSbX6 (X = Cl, Br, I) double perovskites make them suitable for thermoelectric device applications at high temperatures. Based on electronic optical and thermoelectric properties Rb2TlSbCl6 is the best candidate for flexible optoelectronic devices. In this paper, structural optimization of Rb2TlSbX6 (X = Cl, Br, I) double perovskites was conducted utilizing the Wien2k software based on first principle calculations with Perdew-Burke-Ernzerhof's generalized-gradient approximation (PBE-sol approximation). The TB-mBJ potential was employed to compute the accurate band gap of studied materials. The thermoelectric properties are evaluated with BoltzTraP code, showing a predominance of P-type charge carriers in all studied perovskites. This methodological strategy verifies the material's remarkable stability and optical properties and offers a solid framework for examining its potential in optoelectronic devices.

Nonlinear optical response and application of indirect narrow-bandgap SbTe nanosheets

The nonlinear optical properties of antimony telluride (SbTe) crystal with indirect narrow bandgap are investigated, which exhibits superior performance for nonlinear laser modulation in the infrared band. The nonlinear optical coefficients of SbTe nanosheets are determined to be −3.3 cm/GW, −2.3 cm/GW, −1.9 cm/GW and the modulation depths are 5.5 %, 2.0 %, 1.5 % at 400 nm, 800 nm, 1064 nm, respectively. Based on the SbTe-SA, a Yb:GdScO3 laser centered at 1064 nm is achieved with 633 mW maximum output power, 56 fs pulse width and 104 MHz repetition rate. The damage threshold of the SbTe nanosheets is calculated to be exceed 338 GW/cm2, revealing the great potential in high-power laser modulation. This investigation marks the inaugural theoretical and experimental analysis of SbTe’s optical properties and its application in laser modulation, laying the groundwork for future research into indirect narrow-bandgap materials in laser technology.

Electronic and optical properties of the GeS/GeSe heterostructure tuned by in-plane strain

Constructing new two-dimensional (2D) van der Waals (vdW) heterostructures has been widely employed as a convenient and effective strategy for tuning the optoelectronic properties, which is of great significance for applications in integrated nano-optoelectronic devices. In this work, we design a GeS/GeSe vdW heterostructure and systematically investigate its electronic and optical properties by using first-principles calculations. Our results indicate that the pristine GeS/GeSe heterostructure possesses an indirect band gap (∼0.98 eV) and exhibits an intrinsically type-I band alignment. Furthermore, the optoelectronic properties of the GeS/GeSe heterostructure can be effectively modulated by applying in-plane strain. Specifically, an indirect to direct band gap transition and a type-I to type-II band alignment transition can be synchronously realized, when the tensile strain along zigzag direction reaches 2%. Furthermore, the calculated dielectric function also reveals an obvious strain effect on the optical properties of the GeS/GeSe heterostructure. The light absorption coefficient of the GeS/GeSe heterostructure along the zigzag direction can reach to 106 cm−1 level, as the compressive in-plane strain reaches −5%. These findings are expected to play a guidance role in the future design of the optoelectronic devices based on 2D anisotropic heterostructures.

Synthesis and characterization of enhanced azo-azomethine doped PANI/HCl conducting polymers for electrochemical applications

In this study, conducting polymers composed of polyaniline hydrochloric acid (PANI/HCl) with varying concentrations of a newly synthesized azo-azomethine dye (4-(((Z)-2-hydroxy-5-((Z)-(4-hydroxyphenyl)diazenyl)-3-methoxybenzylidene)amino)benzoic acid) were synthesized using a chemical oxidative polymerization technique. The synthesized azo-azomethine was characterized by FTIR, 1H-NMR, 13C-NMR, and HRMS. The effects of varying the concentration of the dopant azo-azomethine in PANI/HCl on its optical, structural, thermal, and electrical properties were examined using FTIR, UV–Vis, XRD, FESEM, TEM, cyclic voltammetry, and electrical impedance spectra. The results indicate that the optical, direct, and indirect band gaps of the doped polymers decreased from 4.48 and 3.96 eV to 3.91 and 2.49 eV, respectively. The crystalline structure and phase transitions in the doped polymers were examined using X-ray diffraction. Cyclic voltammetry demonstrated that the doped polymers exhibited higher electrochemical conductivity compared to the pure polymer, with the specific capacitance increasing from 161.17 to 816.9 F/g. The electrical impedance spectra revealed the bulk resistance and conductivity of the material. Among all the doped polymers, PANI/HCl with an azo-azomethine concentration of 5 × 10−5 M exhibited lower bulk resistance (10 Ω) and higher electrical conductivity (σ = 50.09 × 10−3 S cm−1).

Design considerations of CdSe solar cells for indoor applications under white LED illumination

This work sheds light on the potential of Cadmium Selenide (CdSe) solar cells for indoor applications. CdSe boasts a wide direct bandgap, high carrier mobility, and a high absorption coefficient, making it an attractive candidate for harnessing ambient indoor light. Our study centers around an experimental solar cell architecture composed of FTO/CdSe/PEDOT:PSS/CuI/ITO, which exhibits a power conversion efficiency (PCE) of 6.00 %. Through a meticulous analysis of the core technological aspects of this cell, we successfully replicate the measured current-voltage characteristics and other experimental data, affirming the validity of our simulation modeling approach. Moving forward, we delve into the design and optimization of CdSe-based solar cells under white LED illumination. We emphasize the pivotal role of a double-hole transport layer (HTL) configuration over a single HTL, with a focus on optimizing the alignment between the HTL/back contact and HTL/absorber interfaces. The strategic incorporation of a heavily doped p-type HTL material, boasting both a deep valence band maximum (VBM) and a shallow conduction band minimum (CBM), is identified as paramount, especially for a deep VBM absorber like CdSe. Adding double HTL materials also facilitates efficient hole collection within the CdSe thin film while mitigating undesirable electron-hole recombination at the critical interface between the hole collection layer and the electrode. The implementation of a double HTL configuration based on CuI/ZnTe:Cu or CuI/BCS significantly enhances performance, resulting in a PCE in the order of 20 % under 200 lux and 2900 K LED illumination. Moreover, we introduce the single HTL design to provide other alternatives for efficiency boosting. Upon increasing the work function of the front contact, it is found that the valence band offset between the HTL and the absorber can be engineered, resulting in a PCE above 21.5 %.

Engineering the electronic properties of MoTe2 via defect control

ABSTRACT The remarkable electronic properties of monolayer MoTe2 make it a very adaptable material for use in optoelectronic and nano electronic applications. MoTe2 growth often exhibits intrinsic defects, which significantly influence the material’s characteristics. In this work, we conducted a thorough investigation of the electronic characteristics of intrinsic defects, including point defects, in monolayer MoTe2 using first-principles calculations based on density functional theory (DFT). Our findings indicate that the presence of point defects leads to the formation of n-type properties as the Fermi level situates above the conduction band. Our first-principal density functional theory calculation revealed an appearance of donor level in the band gap close to the conduction band in MoTe2. Our study signifies that the formation energy of a vacancy in a Te atom is lower than that of both a vacancy in a Mo atom and two vacancies in Te atom. This suggests that during the synthesis process, it is more probable for Te atom vacancies to be created. A defect in the pristine monolayer of MoTe2 leads to a slight decrease in the band gap, causing a transition from a direct band gap semiconductor to an indirect band gap semiconductor. The results of our study indicate that the presence of vacancy defects may modify the electronic properties of monolayer MoTe2, suggesting its potential as a new platform for electronic applications. Hence, our analysis offers significant theoretical backing for defect engineering in MoTe2 monolayers and other 2D materials, a critical aspect in the advancement of nanoscale devices with the desired functionality.

Evaluation of the phonon, optoelectronic, photovoltaic, thermoelectric, photocatalytic and thermodynamic properties of the inorganic perovskite CsPbI2Br using Ab initio calculations

Inorganic CsPbI2Br perovskites, derived from cesium, hold potential for use in solar and optoelectronic devices. This study utilized density functional theory calculations to investigate the structural, phonon, electronic, optical, photovoltaic, thermoelectric, thermodynamic, and photocatalytic properties of CsPbI2Br. The phase stability of our compound is thoroughly researched, and it is confirmed that all are thermodynamically and dynamically stable. Formation energy is employed to confirm thermodynamic stability while phonon dispersion is used to confirm dynamical stability. We have computed the electronic properties of CsPbI2Br, such as PDOS, TDOS, and its band structure. The results indicate that the material is a p-type semiconductor which has a direct gap value of 1.50 eV and 1.92 eV using GGA-PBE and TB-mBJ respectively. Higher absorption coefficient, optical conductivity, reflectivity and other optical properties of the CsPbI2Br compound indicate better absorption in the visible spectrum. This distinguishes this substance as an exceptional candidate for optoelectronic devices. Improved utilization of CsPbI2Br in thermoelectric devices is evident from the power factor PF, Seebeck coefficient, figure of merit, and other thermoelectric properties. CsPbI2Br is advantageous in the solar industry due to its external quantum efficiency, open-circuit voltage of 1.92 V, and short-circuit current of 19.67 mA.cm−2. Additionally, the study examined the compound’s thermodynamic properties and examined how the temperature affected its entropy, free energy, enthalpy and heat capacity. Furthermore, it meets the thermodynamic necessary conditions to initiate the water-splitting reaction; the CsPbI2Br compound demonstrates strong photocatalytic performance. This implies that CsPbI2Br may open up new avenues for thermoelectric and optoelectronic experimentation.

Investigation of structural, electronic, optical, mechanical, and solar cell performance of inorganic novel Ca3AsI3 compound through DFT and SCAPS-1D

This manuscript thoroughly examines the structural, mechanical, electrical, and optical attributes of Ca3AsI3 through first principles-based DFT simulations. The mechanical study confirms its stability and robustness despite its brittleness. The direct bandgap at the Γ-point registers at 1.577 (2.14) eV with PBE (HSE)), providing evidence of its semiconducting nature. Phonon dispersion showed that the compound is dynamically stable. Detailed optical insights were obtained, and the SnS2/Ca3AsI3 heterostructure was explored using SCAPS-1D, optimizing absorber thickness, doping density, and bulk/interface defect density. Adjusting the rear electrode’s work function enhances PV productivity. Under optimal conditions, the Ag/FTO/SnS2/Ca3AsI3/Ni structure yields a VOC of 1.11 V, JSC of 22.06 mA/cm2, FF of 85.06 %, and a PCE of 20.88 %. So, this proposed structure may be used as integrated circuit integration, waveguides, and solar cell in a near future.

Oxidation characteristics of copper oxide thin films deposited by direct current sputtering under substrate temperature and post-deposition copper-ion implantation

The oxidation and structural, optical and morphological properties of copper oxide thin films deposited by direct current magnetron sputtering under different substrate temperatures and oxygen (O2) partial pressures, and subsequent 200 keV Cu ion implantation are investigated. The colour of the films progressively changed from yellowish brown to dark brown and oxide phase from Cu2O to Cu4O3 to CuO through mixed phases with increase in oxygen partial pressure from 20 to 90 % of the working pressure and substrate temperature from room temperature (27 °C) to 350 °C. The rate of oxidation and crystallinity of the films substantially increased with increase in substrate temperature. The ion implantation in the room temperature deposited films produced significant crystallization and decrystallization with respect to the ion fluence, and that in 350 °C substrate temperature deposited films instigated Cu-rich phase. The substrate temperature and ion implantation engendered distinctive red shift of the absorption edge and prevalent changes in the interference patterns in the optical spectra of the films. The calculated direct band gap values of the films are in the range of 1.7 to 2.42 eV, which decreased to the range of 1.65 to 2.17 eV on ion implantation. The indirect band gap of the films with predominant Cu4O3 and CuO phases are in the range of 1.23 to 1.49 eV. The refractive index and extinction coefficient of the films at 1100 nm are in the range of 2.1 to 2.5 and 0.03 to 0.12, which increased to the range of 3 to 7 and 0.2 to 0.45, respectively, on ion implantation. The films displayed agglomeration of the particles and directional growth of the agglomerates with respect to O2 partial pressure and substrates temperature, and increase in the size of the particles / agglomerates, and rough surface morphology on ion implantation.

Bulk photovoltaic effect and high mobility in the polar 2D semiconductor SnP2Se6.

The growth of layered 2D compounds is a key ingredient in finding new phenomena in quantum materials, optoelectronics, and energy conversion. Here, we report SnP2Se6, a van der Waals chiral (R3 space group) semiconductor with an indirect bandgap of 1.36 to 1.41 electron volts. Exfoliated SnP2Se6 flakes are integrated into high-performance field-effect transistors with electron mobilities >100 cm2/Vs and on/off ratios >106 at room temperature. Upon excitation at a wavelength of 515.6 nanometer, SnP2Se6 phototransistors show high gain (>4 × 104) at low intensity (≈10-6 W/cm2) and fast photoresponse (< 5 microsecond) with concurrent gain of ≈52.9 at high intensity (≈56.6 mW/cm2) at a gate voltage of 60 V across 300-nm-thick SiO2 dielectric layer. The combination of high carrier mobility and the non-centrosymmetric crystal structure results in a strong intrinsic bulk photovoltaic effect; under local excitation at normal incidence at 532 nm, short circuit currents exceed 8 mA/cm2 at 20.6 W/cm2.

Dielectric, thermal and optical properties of PVDF-based (LaFeO3)0.5 (BaTiO3)0.5 perovskite composite films for advanced technological applications

(1-x)PVDF/(x)LFO-BTO composite films with weight percentages (x = 0, 0.05, 0.1 and 0.15) were prepared by solution casting method. Phase identification was carried out using the X-ray diffraction (XRD) technique revealing different phases (α, β & γ) of PVDF. FTIR results confirmed the presence of different vibrational modes and phases including PVDF phases. AFM and SEM were used to investigate the surface & morphological analysis, the results showed that the surface roughness increased with the concentration of LFO-BTO into PVDF films. From optical absorption spectra, the direct band gap and indirect band gap energies of the PVDF/LFO-BTO were evaluated by incorporating Tauc's relation. The composites experienced a reduction in band gap upon the addition of 0 - 15 wt% of LFO-BTO with an increasing trend in Urbach's energy. The dielectric investigations revealed elevated dielectric constant values across all composites at lower frequency ranges, attributed to interfacial polarization. Specifically, the dielectric constant of 15 % wt of LFO-BTO was found to be much higher (6 times more than the pristine PVDF). Additionally, the dielectric loss was suppressed with increasing filler concentration within the frequency range of 1 KHz to 1 MHz. Impedance spectroscopy analysis depicted a distinctive semi-circular pattern that was linked to the underlying conduction mechanism. The behaviour of ac-conductivity revealed the conduction process following the Nyquist plot. DTA-TGA analysis showed a notable improvement in thermal stability with increasing concentration in the PVDF matrix.

Hf2CO2-based heterojunctions for efficient photocatalytic hydrogen production and highly responsive self-powered flexible photodetector

The heterojunctions based transition metal carbide (MXenes) provides new possibilities for achieving high-performance photodetector. The electronic, mechanical, optical, and photocatalytic properties of the Hf2CO2-based heterojunctions are calculated based on first-principles calculations, and the photocurrent (Iph) and extinction ratio (ER) are calculated based on quantum transport simulations. The Hf2CO2/Sc2CF2, Hf2CO2/Zr2CO2, and Hf2CO2/Sc2CCl2 heterojunctions are ionic semiconductors with indirect bandgap. The Hf2CO2/Sc2CF2 heterojunction exhibits high solar to hydrogen efficiency (ηSTH) of 40.14 % and applying biaxial strain can effectively modulate the ηSTH of the Hf2CO2/Zr2CO2 heterojunction. The Hf2CO2/Zr2CO2 heterojunction has low overpotentials (ηHER) of 0.19 V and exhibits high electron mobility. The photodetector based on the Hf2CO2/Zr2CO2 heterojunction exhibits high Iph, and the photodetector based on the Hf2CO2/Sc2CF2 heterojunction has large ER and sensitivity to infrared and ultraviolet polarized light. The Iph and ER are significant increase by bending the photodetector. Our research indicates the potential applications of the Hf2CO2-based heterojunctions in photocatalytic water splitting and photodetector.

Enhancing the Thermoelectric Performance of BiGa2X4 (X=S, Se) P-type Semiconductors by Optimizing Charge Carrier Concentration or Chemical Potentials

We present an extensive analysis of the structural, electronic, optical, elastic, and thermoelectric properties of compounds, where represents either sulfur () or selenium (). Our approach employed the all-electron full potential linearized augmented plane wave (FP-LAPW) technique, offering a comprehensive understanding of these materials' characteristics. The calculated lattice constants (), the unit cell height (), and the c/a ratio closely match experimental data, affirming the accuracy of our calculations. A pivotal focus of our study was on the electronic properties, including the indirect bandgaps () and (). We found that exhibited an indirect bandgap () of 2.504 eV, while possessed a slightly lower value of 1.878 eV. This variation was primarily attributed to the intricate interactions among bismuth, sulfur, and selenium atoms, particularly involving orbital interactions. Additionally, we explored the optical characteristics of these compounds, determining their maximum absorption wavelengths. exhibited an absorption peak at 4.476 eV, whereas displayed a slightly lower maximum absorption at 3.741 eV. Moreover, showcases a higher dielectric constant, which augments its potential for optoelectronic applications. A critical aspect of our research is the assessment of the elastic properties, elucidating that both compounds exhibited fragility and anisotropy. We observed that at 300 K, the lattice thermal conductivity () for and was measured at and , respectively, indicating low thermal conductivity. At 1000 K, both BiGa2S4, and BiGa2Se4 exhibit significant ZT values of 0.8389 and 0.8722, respectively. The ZT values of the p-type semiconductors are notably higher than those of the n-type. At T=900 K, the optimized ZT values for BiGa2S4, and BiGa2Se4 are found to be 0.82909 and 0.90548, respectively. Achieving these values requires either increasing the concentration of charge carriers to n = 0.11715 x 1022 cm-3 for BiGa2S4 and n = 0.0812 x 1022 cm-3 for BiGa2Se4, or reducing the chemical potentials by 0.40151 Ryd and 0.38001 Ryd, respectively.

A First Principles Study of Stability, Electronic and Thermoelectric Characteristics of Novel High Temperature Half- Heusler Alloys ScAgX (X=Si,Ge,Sn)

To meet the ever-increasing renewable energy demand Half- Heusler (HH) materials can be a potential candidate. Heusler materials are seeking popularity as efficient high-temperature thermoelectric materials. Here we systematically investigated the structural, electronic, mechanical and thermoelectric properties of novel HH compounds ScAgX (X=Si,Ge,Sn) in the framework of the first principles approach. These materials are found to be chemically, mechanically and dynamically stable. Born-Oppenheimer molecular dynamics simulations (BOMD) verify the thermal stability of these materials from 300K to 1100K. The semiconducting nature of these materials is confirmed by the electronic band structure. ScAgX (X=Si,Ge,Sn) have an indirect band gap of 0.37 eV, 0.42 eV and 0.38 eV respectively. A high value of Seebeck coefficient of 6351 μV/K, 6955 μV/K and 6558 μV/K has been obtained at room temperature. ScAgSi shows a high value of electrical conductivity (∼106 S/m) among these compounds at room temperature. The calculated value of the figure of merit (ZT) of ScAgX (X=Si,Ge,Sn) is 0.12, 0.08 and 0.16 at 1100K respectively. Our present investigation shows that these materials can be a potential candidate for high-temperature thermoelectric power generation.

First-principles study of the effect of Dirac phonons on the thermoelectric properties in monolayer Ge2H2

The Dirac phonons have been widely attention due to their unique edge or surface states. However, research on their influence in the realm of thermoelectric transport in semiconductor materials remains limited. Here, we have systematically investigated the geometric structure, stability, electronic, thermal conductivity, and thermoelectric properties of the monolayer Ge2H2 and Ge2 based on density functional theory and the Boltzmann transport equation (BTE). The phonon spectrum of monolayer Ge2H2 exhibits both Hourglass-type and Dirac-type phonon dispersion curves. The band structure of monolayer Ge2H2 reveals a relatively large band gap of 1.02 eV (1.75 eV for HSE), indicating that it is a direct band gap semiconductor. These two features make monolayer Ge2H2 an ideal material for exploring the effect of Dirac phonons on thermoelectric transport properties. In this paper, we determined that the lattice thermal conductivity (κl) in Ge2H2 is 0.59 Wm-1K-1 at 300 K, but undergoes a sharp increase upon removal of H atoms. This is mainly attributed to the disappearance of the Dirac phonons and the change of lattice vibration modes by removing the H atoms. While also exhibiting high carrier mobilities (134.86 cm2/Vs for holes) and extended scattering time (4.22 × 10−14 s for holes), indicative of excellent thermoelectric performance. With increasing temperature, the ZTmax of p-type doping reaches 0.63 at 700 K in Ge2H2. Remarkably, at 300K, the Hourglass-type phonon contributes only 5.94% to κl, while the Dirac phonon contributes 3.44%. Further analysis reveals that the Dirac phonon within Hourglass-type in monolayer Ge2H2 contributes 2.5% to the ZTmax at 300K. Our investigation elucidates the impact of Dirac phonons on thermoelectric properties, providing valuable insights for future design and exploration of high-ZT thermoelectric materials.

Performance and sensitivity mechanism of the 1,3,5-trinitro-2,4,6-trinitroaminobenzene (TNTNB)

Recently, a new type of high-energy explosive (TNTNB) has been synthesized. Before fully understanding its detonation performance and safety features, it is necessary to conduct certain studies on its basic physical properties. For this purpose, we have employed first-principles methods to investigate the structural, electronic, vibrational, and thermal properties of TNTNB. The optimized lattice parameters of TNTNB crystals differ from the experimental values by less than 2 %. The electronic properties calculation results show that TNTNB has an indirect bandgap of 2.1508 eV. The phonon dispersion and density of phonon states indicate that its phonon bath modes region is 0–245 cm−1, and the doorway modes region is 245–735 cm−1. Additionally, the calculated energy transfer rate is 3.460 × 1012 J/K/mol, and the phonon-vibration coupling coefficient is 3.31. The zero-point energy calculated from the density of phonon states is 1669.06 kJ/mol, and the isochoric heat capacity at 300 K is 1441.48 J/K/mol.

Computational Study of the Structural, Mechanical, Electronic, Optical and Thermal properties of BaLiX (X =P, As, Sb) perovskites

This study explores the structural, optical, mechanical, electronic, and thermal characteristics of ionic semiconductor compounds BaLiX (X =P, As, Sb) using Density Functional Theory (DFT). A comprehensive analysis of BaLiX (X =P, As, Sb) is conducted, proving that the estimated and observed lattice parameters coincide well and confirming mechanical stability through elastic stiffness constants. Electronic band structures reveal direct bandgap semiconductor properties with values of 0.70 eV, 0.30 eV, and 0.95 eV for BaLiP, BaLiAs, and BaLiSb, respectively, suggesting specific applications such as mid-infrared photodetectors, terahertz devices, and near-infrared sensors. Optical property analyses, including energy loss function, reflectivity, refractive index, and absorption coefficient, highlight the potential of these materials for optoelectronic and photovoltaic applications. Despite elastic anisotropy, optical anisotropy remains minimal. The materials exhibit potential for use as thermal barrier coatings (TBC) due to their comparatively lower Debye temperature (D), minimum thermal conductivity (Kmin) and lattice thermal conductivity (kph). Moreover, heat capacity calculations and thermal coefficient of expansion are also calculated.

Single-Layer InGeS: Robust direct Bandgap, super high electron Mobility, long-lived Carriers, and Ohmic contact for Next-Generation Field-Effect transistors

Two-dimensional (2D) materials holding appropriate bandgaps, high carrier mobility, and long carrier lifetime require to be urgently explored as electronic devices such as field effect transistors (FETs) become more and more miniaturized. Herein, single-layer (SL) InGeS is thoroughly investigated using first-principles calculations. Theoretical results confirm SL InGeS has nice thermal and dynamical stability at 300 K. SL InGeS holds a direct bandgap of 1.28 eV by HSE06, and its electrons and holes are inherently located at different atomic regions. In the visible range, SL InGeS displays a maximum optical absorption of ∼ 5 × 105 cm−1, surpassing that of most known 2D materials. Furthermore, SL InGeS possesses high electron mobility (∼11100 cm2 V−1 s−1) and relatively low hole mobility (∼1000 cm2 V−1 s−1), and its carrier lifetime is as long as 4.99 ns. In addition, an Ohmic contact is designed in the graphene/InGeS heterojunction, implying small current resistance. In brief, all these scientific findings promise SL InGeS is a hopeful candidate in ultrathin FET devices.

Theoretical investigation into potential thermoelectric material Monolayer InI with direct bandgap and ultralow lattice thermal conductivity

Monolayer metal iodides are garnering widespread attention due to their ultralow lattice thermal conductivity and their potential applications in the field of thermoelectrics. Here, we utilized first-principles calculations and Boltzmann transport theory to thoroughly investigate the thermoelectric behavior of monolayer InI. Results indicate that this material functions as a direct bandgap semiconductor and features an exceptionally low lattice thermal conductivity of 0.27 W m−1K−1 at 300 K, a result of its low group velocities and short phonon lifetimes. Furthermore, transport coefficients were calculated with enhanced precision through the Wannier interpolation method, incorporating the HSE06 hybrid functional and spin-orbit coupling (SOC) effects. Remarkably, the maximum thermoelectric figure of merit (ZT) values for monolayer InI demonstrate substantial growth with increased temperatures, surging from 0.31 at 300 K to 1.20 at 450 K for p-type, and escalating from 0.26 at 300 K to 0.72 at 450 K for n-type. These promising low-temperature thermoelectric properties exhibited by monolayer InI suggest its suitability for integration into the production of thermoelectric devices.