Optoelectronic Devices Research Articles

Influence of porous media and substrate rotation on AlN growth in MNVPE reactors based on CFD simulations

AlN is an important III-V wide-bandwidth semiconductor material. Its maximum (ultra-wide) direct bandgap of up to 6.2 eV at room temperature and excellent physical properties make it have great application prospects in the fields of high-power high-frequency electronics and high-efficiency optoelectronic devices. In this paper, based on Computational Fluid Dynamics (CFD), the finite volume method was employed to investigate the process of growing AlN thin films by MNVPE using CFD simulation software for three-dimensional numerical simulation. By optimizing the chamber structure, it was devoted to improving the growth rate and uniformity of AlN thin films. Different thicknesses of porous media were placed in front of the substrate respectively, and the flow field analysis showed that the presence of eddy currents can be effectively suppressed to reduce the pre-reaction, and the best growth effect was achieved when the thickness reached 7 cm. With the increasing of porosity, more gas reached the substrate surface and improved the growth rate of AlN films. Secondly, for the 90° substrate, substrate rotation created a pumping effect and the growth rate was higher with the increase of the rotation speed. At 160 rpm, the growth rate reached 11.29 μm/h and the coefficient of variation decreased to less than 5 %.

Interface Characterization of Graphene‐Silicon Heterojunction Using Hg Probe Capacitance–Voltage Measurement

AbstractInvestigating the intrinsic properties of the Schottky interface between graphene and 3D bulk silicon is crucial. However, the semiconductor technology introduces extra doping and defects in graphene, which significantly disturbs the property of the graphene‐silicon interface. Here, the interface parameters of graphene/n‐Si heterojunction are derived by the damage‐free Hg‐probe capacitance–voltage measurement. Due to its low‐density states, the Fermi level of graphene can be pushed upward, which results in a lower Schottky barrier height (ΦB0) of Hg/graphene/n‐Si (HGS) heterostructure than that of Hg/n‐Si (HS) structure. Additionally, the series resistance (Rs) of HGS becomes lower than that of HS, which can be attributed to the narrowed depletion layer width (WD) and the decreased interface state density (Nit). Furthermore, the frequency characteristic is also investigated. Because of the weak interface state charge trapping–detrapping process and the decreased Nit at high frequency, electrons will accumulate in graphene, and the Fermi level will be pushed up. Hence, the ΦB0 and Rs will decrease with increasing frequency. This study contributes to a deep understanding of the graphene/silicon heterojunction interfaces, which is crucial for designing and optimizing the new electronic and optoelectronic devices based on 2D/3D heterostructure.

Influence of porous media and substrate rotation on AlN growth in MNVPE reactors based on CFD simulations

AlN is an important III-V wide-bandwidth semiconductor material. Its maximum (ultra-wide) direct bandgap of up to 6.2 eV at room temperature and excellent physical properties make it have great application prospects in the fields of high-power high-frequency electronics and high-efficiency optoelectronic devices. In this paper, based on Computational Fluid Dynamics (CFD), the finite volume method was employed to investigate the process of growing AlN thin films by MNVPE using CFD simulation software for three-dimensional numerical simulation. By optimizing the chamber structure, it was devoted to improving the growth rate and uniformity of AlN thin films. Different thicknesses of porous media were placed in front of the substrate respectively, and the flow field analysis showed that the presence of eddy currents can be effectively suppressed to reduce the pre-reaction, and the best growth effect was achieved when the thickness reached 7 cm. With the increasing of porosity, more gas reached the substrate surface and improved the growth rate of AlN films. Secondly, for the 90° substrate, substrate rotation created a pumping effect and the growth rate was higher with the increase of the rotation speed. At 160 rpm, the growth rate reached 11.29 μm/h and the coefficient of variation decreased to less than 5 %.

Optically Mediated Nonvolatile Resistive Memory Device Based on Metal-Organic Frameworks.

Metal-organic frameworks (MOFs), characterized by tunable porosity, high surface area, and diverse chemical compositions, offer unique prospects for applications in optoelectronic devices. However, the prevailing research on thin-film devices utilizing MOFs has predominantly focused on aspects such as information storage and photosensitivity, often neglecting the integration of the advantages inherent in both photonics and electronics to enhance optical memory. This work demonstrates a light-mediated resistive memory device based on a highly oriented porphyrin-based MOFs film, in which the resistance state of the memristor is modulated by light, realizing the integration of the perception and storage of optical information. The memristor shows excellent performance with a wide light range of 405-785nm and a persistent photoconductivity phenomenon up to 8.3 × 103 s. Further mechanistic studies have revealed that the resistive switching effect in the memristor is primarily associated with the reversible formation and annihilation of Ag conductive filaments.

Morphological, structural, and electronic properties of green synthesized ZnO nanoparticles by experimental and DFT+U method – A review

In these decades, researchers have paid much attention to green synthesis methods because of their low cost and eco-friendliness. Among all other semiconductors, ZnO nanoparticles have huge applications in optoelectronics devices, solar cells, photocatalysis, transistors, etc. This review article explains the green synthesis methods and factors affecting the morphology of ZnO nanoparticles. The morphology shows different structures such as nanowires, cubic, hexagonal, flower-like structures, etc. The XPS peaks Zn-2p1/2, Zn-2p3/2, and O-1S suggest that the synthesized nanoparticles are ZnO. The theoretical review part explains the electronic and structural properties of wurtzite ZnO nanoparticles. The implementation of the Hubbard-U scheme in the d and p shells using Local Density Approximation (LDA) and Generalized Gradient Approximation (GGA) shows the drastic change in the electronic and structural properties of ZnO nanoparticles. The optimized lattice parameters and band gap using Hubbard parameters by different DFT codes are tabulated. Also, we compared computational and experimental results.

Plasma-Etched Black GaAs Nanoarrays with Gradient Refractive Index Profile for Broadband, Omnidirectional, and Polarization-Independent Antireflection.

Black GaAs nanotip arrays (NTs) with 3300 nm lengths were fabricated via self-masked plasma etching. We show, both experimentally and numerically, that these NTs, with three gradient refractive index layers, effectively suppress Fresnel reflections at the air-GaAs interface over a broad range of wavelengths. These NTs exhibit exceptional UV-Vis light absorption (up to 99%) and maintain high NIR absorption (33-60%) compared to bare GaAs. Moreover, possessing a graded layer with a low refractive index (n = 1.01 to 1.12), they achieve angular and polarization-independent antireflection properties exceeding 80° at 632.8 nm, aligning with perfect antireflective coating theory predictions. This approach is anticipated to enhance the performance of optoelectronic devices across a wide range of applications.

Enhanced ambient-stability and charge transport property of the CsPbBr3@Polyaniline

Although all-inorganic lead halide perovskites (CsPbX3 (X = Cl, Br, I)) have received widespread attention due to excellent optoelectronic properties, their low carrier mobility and poor stability have limited their application in photodetection. In this study, to alleviate these problems, CsPbBr3@Polyaniline composite is fabricated by passivating CsPbBr3 quantum dots (QDs) into a CSA-doped polyaniline conducting polymer. Notably, polyaniline is employed as a protective layer to block the structure damage of CsPbBr3 QDs against water, light and heat. The contact between polyaniline and CsPbBr3 QDs forms a type II heterojunction for charge transfer, which greatly reduces the recombination rate of charge carriers compared to pristine CsPbBr3 QDs. Benefiting from the high stability and enhanced charge mobility, CsPbBr3@Polyaniline-based photodetector achieves improved photocurrent signal and optical response time. The results demonstrate that the surface passivation could resolve the crucial stability problem and simultaneously facilitate the superior performance of perovskite optoelectronic devices.

Plasma-Etched Black GaAs Nanoarrays with Gradient Refractive Index Profile for Broadband, Omnidirectional, and Polarization-Independent Antireflection

Black GaAs nanotip arrays (NTs) with 3300 nm lengths were fabricated via self-masked plasma etching. We show, both experimentally and numerically, that these NTs, with three gradient refractive index layers, effectively suppress Fresnel reflections at the air–GaAs interface over a broad range of wavelengths. These NTs exhibit exceptional UV-Vis light absorption (up to 99%) and maintain high NIR absorption (33–60%) compared to bare GaAs. Moreover, possessing a graded layer with a low refractive index (n = 1.01 to 1.12), they achieve angular and polarization-independent antireflection properties exceeding 80° at 632.8 nm, aligning with perfect antireflective coating theory predictions. This approach is anticipated to enhance the performance of optoelectronic devices across a wide range of applications.

First principle investigations of opto-electronic and thermoelectric response of A2TlAsX6 (A = K, Rb; X = Cl, Br) compounds

We have investigated the structural, electronic, optical, and thermoelectric behavior of halide-based double perovskites A2TlAsX6 (A = K, Rb; X = Cl, Br) compounds to reveal their potential in various opto-electronic and thermoelectric applications using first-principle calculations. For the computation of the various properties of A2TlAsX6 (A = K, Rb; X = Cl, Br) compounds, we have used approximations available within density functional theory (DFT). The energy bands and density of states have been used to elucidate the electronic response of the studied compounds, while the interpretation of optical properties is presented in terms of dielectric tensor, absorption coefficient, reflectivity, refraction and energy loss spectra. The investigated compounds exhibit a direct band gap within the energy range of 1.36 to 2.24 eV, indicating the promising nature of these compounds for diverse optoelectronic applications. Moreover, thermoelectric properties such as the figure of merit, power factor, Seebeck coefficient, specific heat, electric and thermal conductivity have also been computed for the studied compounds. Our investigation unveils the remarkable optoelectronic characteristics of the studied perovskites, which can be attributed to their advantageous bandgap and highly effective light absorption capabilities. Furthermore, these perovskites showcase exceptional thermodynamic stability, elevated electrical conductivity, favorable figure of merit (ZT) values, and reduced thermal conductivities. These findings suggest their suitability for applications in optoelectronic devices and thermoelectric applications. In this study, it is found that A2TlAsBr6 compounds exhibit significant absorption in the visible spectrum, rendering them more favorable for optoelectronic applications compared to A2TlAsCl6 compounds. Conversely, for thermoelectric applications, the Cl-based perovskites studied show greater promise than their Br-based counterparts. The modified Becke–Johnson (mBJ) potential emerges as the most precise approach for analyzing the electronic, optical, and thermoelectric characteristics of A2TlAsX6 (where A = K, Rb; X = Cl, Br) perovskites, surpassing other approximations utilized in present study.

Piezotronically tuned photosensitivity in ZnO varistor-type interface devices

The study of piezotronic and piezo-phototronic features in semiconducting piezoelectrics has gained considerable attention for optimizing electronic and optoelectronic device performance. In this study, we explore the photocurrent response within a ZnO varistor-type interface device and examine its UV photosensitivity enhancement through piezo-phototronic modulation of the potential barriers at grain boundaries. Doped ZnO bicrystals were synthesized using the epitaxial solid-state transformation method with polarization vectors perpendicular to the interface. The vectors can be directed both into and out of the interfaces depending on the crystallographic orientation of the crystals designated as (0001̅)|(0001̅) and (0001)|(0001) interfaces, respectively. These varistor-type boundaries demonstrate an exceptional photoelectric response to UV photons. Furthermore, our results indicate that the photoresponsivity of bicrystals with (0001)|0001 crystallographic orientation can be further enhanced under piezo-phototronic influence. Application of compressive stress of 100 MPa not only increased photocurrent formation by 1000 % but also boosted photosensitivity by 1400 %, attributed to the elevated double Schottky barrier (DSB) height at the interface resulting from mechanical loading on the bicrystal. Our findings highlight the significant role of piezoelectrically tuned potential barriers at grain boundaries in enhancing the separation and extraction of photogenerated excitons for photocurrent formation. This study introduces the engineered varistor-type interface as a promising candidate for future optoelectronic devices and contributes to our understanding of the piezo-phototronic concept in semiconductor-semiconductor interface devices.

Investigating structural and optoelectronic properties of Cr-substituted ZnSe semiconductors

The optoelectronic and structural characteristics of the Zn1−xCrxSe (0 ≤ x ≤ 1) semiconductor are reported by employing density functional theory (DFT) within the mBJ potential. The findings revealed that the lattice constant decreases with increasing Cr concentration, although the bulk modulus exhibits the opposite trend. ZnSe is a direct bandgap material; however, a change from direct to indirect electronic bandgap has been seen with Cr presence. This transition is caused by structural alterations by Cr and defects forming, which results in novel optical features, including electronic transitions. The electronic bandgap decreases from 2.769 to 0.216 eV, allowing phonons to participate and improving optical absorption. A higher concentration of Cr boosts infrared absorption and these Cr-based ZnSe (ZnCrSe) semiconductors also cover a wider spectrum in the visible range from red to blue light. Important optical parameters such as reflectance, optical conductivity, optical bandgap, extinction coefficient, refractive index, magnetization factor, and energy loss function are discussed, providing a theoretical understanding of the diverse applications of ZnCrSe semiconductors in photonic and optoelectronic devices.

Implementation of excellent spin-filtering effect in half-metallic electrode-based single-molecule optoelectronic devices

The application of half-metallic materials in single-molecule optoelectronic devices opens a promising way in advancing device performance and functionality, thus addressing a research question of significance. Here we propose a series of single-molecule devices with half-metallic FeN4-doped armchair graphene nanoribbon as electrodes and metalloporphyrin (MPr) molecules as photoresponsive materials for photon harvesting, which are driven by photogalvanic effects (PGEs). Through the quantum transport simulations, we systematically investigated the spin-polarized photocurrents under the linearly polarized light illumination in these devices. Since the exclusive opening only exists in the spin-up channel of the half-metallic nanoribbons, these devices can generate a large photocurrent in the spin-up direction whereas suppressing the spin-down photocurrent. Consequently, they exhibit an effective spin-filtering effect at numerous photon energies. Our study unveils the excellent spin-filtering effect achieved in single-molecule optoelectronic devices with half-metallic electrodes, showing instructive significance for the future design of new optoelectronic devices.

A systematic first-principles investigation of the structural, electronic, mechanical, optical, and thermodynamic properties of Half-Heusler ANiX (ASc, Ti, Y, Zr, Hf; XBi, Sn) for spintronics and optoelectronics applications.

This paper is the first to look at the structural, electronic, mechanical, optical, and thermodynamic properties of the ANiX (ASc, Ti, Y, Zr, Hf; XBi, Sn) half-Heusler (HH) using DFT based first principles method. The lattice parameters that we have calculated are very similar to those obtained in prior investigations with theoretical and experimental data. The positive phonon dispersion curve confirm the dynamical stability of ANiX (ASc, Ti, Y, Zr, Hf; XBi, Sn). The electronic band structure and DOS confirmed that the studied materials ANiX (ASc, Ti, Y, Zr, Hf; XBi, Sn) are direct band gap semiconductors. The investigation also determined significant constants, including dielectric function, absorption, conductivity, reflectivity, refractive index, and loss function. These optical observations unveiled our compounds potential utilization in various electronic and optoelectronic device applications. The elastic constants were used to fulfill the Born criteria, confirming the mechanical stability and ductility of the solids ANiX (ASc, Ti, Y, Zr, Hf; XBi, Sn). The calculated elastic modulus revealed that our studied compounds are elastically anisotropic. Moreover, ANiX (ASc, Ti, Y, Zr, Hf; XBi, Sn) has a very low minimum thermal conductivity (Kmin), and a low Debye temperature (θD), which indicating their appropriateness for utilization in thermal barrier coating (TBC) applications. The Helmholtz free energy (F), internal energy (E), entropy (S), and specific heat capacity (Cv) are determined by calculations derived from the phonon density of states.

Control of Hybrid Exciton Lifetime in MoSe2/WS2 Moiré Heterostructures.

Hybrid excitons, characterized by their strong oscillation strength and long lifetimes, hold great potential as information carriers in semiconductors. They offer promising applications in exciton-based devices and circuits. MoSe2/WS2 heterostructures represent an ideal platform for studying hybrid excitons, but how to regulate the exciton lifetime has not yet been explored. In this study, layer hybridization is modulated by applying electric fields parallel or antiparallel to the dipole moment, enabling us to regulate the exciton lifetime from 1.36 to 4.60ns. Furthermore, the time-resolved photoluminescence decay traces are measured at different excitation power. A hybrid exciton annihilation rate of 8.9 × 10-4cm2s-1 is obtained by fitting. This work reveals the effects of electric fields and excitation power on the lifetime of hybrid excitons in MoSe2/WS2 1.5° moiré heterostructures, which play important roles in high photoluminescence quantum yield optoelectronic devices based on transition-metal dichalcogenides heterostructures.

Advances and challenges in molecular engineering of 2D/3D perovskite heterostructures.

Organic-inorganic hybrid perovskites have been intensively studied in past decades due to their outstanding performance in solar cells and other optoelectronic devices. Recently, the emergence of two-dimensional/three-dimensional (2D/3D) heterojunctions have enabled many solar cell devices with >25% power conversion efficiency, driven by advances in our understanding of the structural and photophysical properties of the heterojunctions and our ability to control these properties through organic cation configuration in 2D perovskites. In this feature article, we discuss a fundamental understanding of structural characteristics and the carrier dynamics in the 2D/3D heterojunctions and their impact factors. We further elaborate the design strategies for the molecular configuration of organic cations to achieve thorough management of these properties. Finally, recent advances in 2D/3D heterostructures in solar cells, light-emitting devices and photodetectors are highlighted, which translate fundamental understandings to device applications and also reveal the remaining challenges in ligand design for the next generation of stable devices. Future development prospects and related challenges are also provided, with wide perspectives and insightful thoughts.

Covalent Bond Torsion-Enabled Unique Crystal-Phase Transformation of an Organic Semiconductor for Multicolor Light-Emitting Transistors.

High-mobility and color-tunable highly emissive organic semiconductors (OSCs) are highly promising for various optoelectronic device applications and novel structure-property relationship investigations. However, such OSCs have never been reported because of the great trade-off between mobility, emission color, and emission efficiency. Here, we report a novel strategy of molecular conformation-induced unique crystalline polymorphism to realize the high mobility and color-tunable high emission in a novel OSC, 2,7-di(anthracen-2-yl) naphthalene (2,7-DAN). Interestingly, 2,7-DAN has unique crystalline polymorphism, which has an almost identical packing motif but slightly different molecular conformation enabled by the small bond rotation angle variation between anthracene and naphthalene units. More remarkably, the subtle covalent bond rotation angle change leads to a big change in color emission (from blue to green) but does not significantly modify the mobility and emission efficiency. The carrier mobility of 2,7-DAN crystals can reach up to a reliable 17 cm2 V-1 s-1, which is rare for the reported high-mobility OSCs. Based on the unique phenomenon, high-performance light-emitting transistors with blue to green emission are simultaneously demonstrated in an OSC crystal. These results open a new way for designing emerging multifunctional organic semiconductors toward next-generation advanced molecular (atomic)-scale optoelectronics devices.

Pressure and atomic size effects of IV cation on mechanical and electronic properties of Zn-IV-N2 (IV[dbnd]Si, Ge and Sn): First principles calculation

Zn-IV-N2 compounds, incorporating Si, Ge, and Sn, have emerged as pivotal materials for their mechanical and electronic properties, influencing optoelectronic devices and photovoltaic applications. Employing density functional theory (DFT), we comprehensively investigate the structural, elastic, mechanical, and electronic characteristics of ZnIVN2 (IVSi, Ge, Sn) under ambient and pressure conditions up to 20 GPa. Our findings suggest that a larger atomic size of the group IV cation can be more easily compressed than a smaller size. The mechanical stability criteria and the phonon dispersion show mechanical and dynamic stability in both ambient pressure and under high pressure up to 20 GPa. The ZnSiN2 and ZnGeN2 exhibit linear increments in bulk modulus (B), shear modulus (G), and Young's modulus (E) under pressure, while ZnSnN2 experiences a decrease in G and E. Notably, the energy gap of ZnSiN2, ZnGeN2, and ZnSnN2 (4.62 eV indirect, 2.82 eV, 1.16 eV, respectively) increases with pressure due to higher N s orbital energy, approaching the UV region. In the valence band, a hybridization of N p and Si/Ge/Sn p orbitals is observed, offering opportunities to tailor the band gap for optimal applications in optoelectronic devices. Preferentially adjusting group-IV elements over group-II elements is recommended for optimizing band gap modulation. The correlation between larger atomic size and decreased band gap energy highlights the potential to fine-tune material properties through controlled variations in group-IV elements.

Ultrathin, High-Aspect-Ratio Bismuth Sulfohalide Nanowire Bundles for Solution-Processed Flexible Photodetectors.

In this study, a novel synthesis of ultrathin, highly uniform colloidal bismuth sulfohalide (BiSX where X = Cl, Br, I) nanowires (NWs) and NW bundles (NBs) for room-temperature and solution-processed flexible photodetectors are presented. High-aspect-ratio bismuth sulfobromide (BiSBr) NWs are synthesized via a heat-up method using bismuth bromide and elemental S as precursors and 1-dodecanethiol as a solvent. Bundling of the BiSBr NWs occurs upon the addition of 1-octadecene as a co-solvent. The morphologies of the BiSBr NBs are easily tailored from sheaf-like structures to spherulite nanostructures by changing the solvent ratio. The optical bandgaps are modulated from 1.91 (BiSCl) and 1.88eV (BiSBr) to 1.53eV (BiSI) by changing the halide compositions. The optical bandgap of the ultrathin BiSBr NWs and NBs exhibits blueshift, whose origin is investigated through density functional theory-based first-principles calculations. Visible-light photodetectors are fabricated using BiSBr NWs and NBs via solution-based deposition followed by solid-state ligand exchanges. High photo-responsivities and external quantum efficiencies (EQE) are obtained for BiSBr NW and NB films even under strain, which offer a unique opportunity for the application of the novel BiSX NWs and NBs in flexible and environmentally friendly optoelectronic devices.

Perovskite Grown in Gallium Nitride Nanowire Matrix for Stable and High‐Efficiency X‐Ray Detection

AbstractHigh‐quality quasi‐2D perovskites in a GaN nano‐wire matrix are grown to build a 3D hetero‐structure for high‐performance X‐ray sensing. In the 3D hetero‐structure, GaN nano‐wire matrix serves as an n‐type charge collector that can rapidly extract carriers through the bulk film of the perovskite layer. Together with a p‐type top electrode, a p–i–n diode with the 3D hetero‐structure is built, that exhibits a rectified current–voltage characteristic. After analyzing the interface energy alignment, it is found that the fermi levels of the perovskite and GaN are aligned in the dark, and a quasi‐fermi level splits upon illumination, introducing a built‐in electrical field at the interface. As a result, strong photo‐induced current is observed from the diode without an external field. Finally, the 3D diode for X‐ray detection demonstration is used, revealing a sensitivity of 308.9 µC Gyair−1 cm−2 at an exceptionally low applied field of 0.125 V µm−1. The X‐ray‐induced signal from the 3D diode is stable after 155 cycles of X‐ray irradiation under a constant electric field. This demonstration informs a new 3D architecture for high‐performance X‐ray sensing, and it shows that GaN is a robust n‐type interface for perovskite optoelectronic devices.

Preparation of brittle ITO microstructures using Laser-Induced forward transfer technology

The performance of transparent conductive microstructures plays a significant role in determining the device efficiency. The fabrication of ITO microstructures on the flexible optoelectronic devices remains challenging because of the high-temperature processing requirements and brittleness of the ceramic material. This paper highlights a three-dimensional microfabrication technique that combines sacrificial layer etching and laser-induced transfer. By studying the donor material thickness and the laser energy density, control of the sacrificial layer transfer thrust was achieved to yield an optimal microstructure performance. Different shapes of ITO transparent conductive microstructures were fabricated on polydimethylsiloxane (PDMS) surfaces, demonstrating structural integrity, visible light transmittances > 90 %, and resistivities of ≤ 8 × 10−4 Ω·cm. Finite element analysis was employed to simulate the impact transfer of the donor material onto the receiving substrate, thereby elucidating the energy-absorbing protective role of the flexible PDMS layer. Effective control of the transfer force was identified as a crucial factor in achieving the successful transfer of brittle films. This high-precision and rapid array processing approach meets the demands of automated batch manufacturing, indicating its potential for use in patterned processing on flexible substrates, as an alternative to lithographic techniques. This technique could be applied in the preparation of electronic skins and flexible devices. Additionally, for the first time, a 3 × 3 pixel resistive array sensor was integrated on a Ag nanowires/PDMS surface, demonstrating array pressure-sensing capabilities at pressures of 0–80 kPa. This study represents a significant step towards the development of multifunctional flexible optoelectronic devices.