Electron-hole Research Articles

Dual Electric Field Coupling with Tunable Schottky Barrier Synergistically Regulating Electronic Configuration in CoP@Ni‐CdS Heterojunction for Efficient Photocatalytic H2 Evolution

AbstractDesigning and exploiting visible‐light‐responsive materials that converts solar into chemical energy is promising in achieving green energy sustainability, but addressing low electron–hole separation efficiency and sluggish surface kinetic process remains formidable challenges. Herein, a novel CoP@Ni‐CdS Schottky junction composed of Ni‐doped CdS nanorods and quasi‐metallic CoP nanoparticles is constructed via a simple hydrothermal–calcination method. Experiments and theoretical calculations demonstrate that magnetic Ni‐doping not only induces a spin‐polarized electric field and enhances the built‐in interfacial electric field strength, but also rises the Schottky barrier height at the heterointerface, which synergistically accelerates the separation efficiency of photoinduced charges and modulates the electronic configuration of the active site to optimize the adsorption–desorption behaviors for H2O molecules and H* intermediates. Therefore, the designed CoP@Ni‐CdS catalyst exhibits an exceptional photocatalytic performance with H2 evolution rate of 42.14 mmol g−1 h−1 with the apparent quantum efficiencies of 16.8% at 420 nm, which is 14.14 and 2.21 times higher than that of pristine CdS and Ni‐CdS, respectively. This work provides in‐depth insights into fabricating dual electric fields, tuning the Schottky barrier and modulating the electronic configuration of active sites in Schottky heterojunction for ameliorative photocatalytic activity.

Core/Shell ZnO/TiO2, SiO2/TiO2, Al2O3/TiO2, and Al1.9Co0.1O3/TiO2 Nanoparticles for the Photodecomposition of Brilliant Blue E-4BA

The synthesis and characterization of ZnO/TiO2, SiO2/TiO2, Al2O3/TiO2, and Al1.9Co0.1O3/TiO2 core/shell nanoparticles (NPs) is reported. The NPs were used for photocatalytic degradation of brilliant blue E-4BA under UV and visible light irradiation, monitored by high-performance liquid chromatography and UV-vis absorption spectroscopy. The size of the NPs ranged from 10 to 30 nm for the core and an additional 3 nm for the TiO2 shell. Al2O3/TiO2 and Al1.9Co0.1O3/TiO2 showed superior degradation under UV and visible light compared to ZnO/TiO2 and SiO2/TiO2 with complete photodecomposition of 20 ppm dye in 20 min using a 10 mg/100 mL photocatalyst. The “Co-doped” Al1.9Co0.1O3/TiO2 NPs show the best performance under visible light irradiation, which is due to increased absorption in the visible range. DFT-calculated band structure calculations confirm the generation of additional electronic levels in the band gap of γ-Al2O3 through Co3+ ions. This indicates that Co-doping enhances the generation of electron–hole pairs after visible light irradiation.

Modification of opto‐electrical behavior of polyvinyl chloride by infusion of SrTiO3 nanofiller synthesized via green route

AbstractEnhancing the opto‐electrical properties of polymer is crucial for optoelectronic devices. This study emphasis the synthesis of strontium titanate (SrTiO3) nanoparticles using a green sol–gel method and incorporates them into polyvinyl chloride (PVC) to create nanocomposite films via solution casting. The structural, optical, thermal, and electrical properties of PVC with SrTiO3 at concentrations of 1, 3, and 5 wt.% were examined. Better crystallinity was obtained with filler incorporation. Fourier transform infrared shows the physical interaction between nanofiller and the matrix. SEM results suggested that SrTiO3 nanofiller are well distributed in PVC surface. UV–Vis spectroscopy was used to study optical behavior of the nanocomposites. Optical bandgap energy decreased from 3.2 to 2.5 eV with increased concentration of SrTiO3 in PVC matrix. Photoluminescence results show the reduction of electron hole recombination rate. The integration of SrTiO3 nanofiller into the PVC matrix improved the thermal stability, dielectric constant, and the overall performance of the prepared nanocomposite films, making them suitable for high‐temperature optoelectronic and energy storage applications. The green synthesis of SrTiO3 nanofiller also ensures the environmental benefits, high purity, and homogeneity, leading to consistent enhancements in the PVC/SrTiO3 composites. These improvements highlight their potential for advanced optoelectronic devices requiring efficient and durable materials.

The Effect of Heat Treatment on the Sol–Gel Preparation of TiO2/ZnO Catalysts and Their Testing in the Photodegradation of Tartrazine

This study aims to synthesize TiO2/ZnO powders and to study the effect of heat treatment on their photocatalytic ability against the Tartrazine anionic dye. The as-obtained powders with the following compositions—90TiO2/10ZnO and 10TiO2/90ZnO (mol%)—were obtained by the sol–gel technique. The prepared gels were annealed at 500 °C and 700 °C and subsequently characterized by XRD, UV–Vis, and SEM methods. The single crystalline phase of TiO2, which has been detected at up to 500 °C is anatase, while for ZnO, it is the hexagonal wurtzite structure. Further increases in the temperature (700 °C) led to the appearance of rutile in the samples. The SEM analysis demonstrated that the binary oxide materials had irregular shaped particles with a tendency to agglomerate. The UV–Vis spectra of the gels exhibited a red shift in the cut-off of the 90TiO2/10ZnO sample compared with pure Ti(IV) butoxide. Photocatalytic tests showed that the investigated samples possessed photocatalytic activity toward Tartrazine. Compared with TiO2, the prepared TiO2/ZnO photocatalysts showed superior properties in the photodegradation of a Tartrazine water solution. The target photocatalysts’ enhanced photocatalytic activities can be explained by their reduced band gap energy, improved surface physicochemical characteristics, separation of photo-induced electron–hole pairs, and lowered recombination rate. Higher photocatalytic activity was observed for powders annealed at 500 °C, with the 10TiO2/90ZnO (mol%) sample exhibiting the highest photocatalytic degradation of the used organic dye.

Dual‐functional UiO‐66/g‐C3N4 composites for photocatalytic pesticide removal and in situ adsorption of phosphate byproducts in water

AbstractBACKGROUNDWith the increasing global demand for food, a significant amount of organophosphorus pesticides is applied to farmland, leading to pollution as they are discharged into natural water bodies with agricultural runoff. This study employed a coupling approach, utilizing a 6:4 mass ratio of zirconium‐based metal–organic framework UiO‐66 and g‐C3N4 through a grinding and annealing method to construct a Z‐type heterojunction composite material named UG 6:4.RESULTSThis material is employed for photocatalytic removal of the representative organophosphorus pesticide, dichlorvos (DDVP), from water and simultaneous in situ adsorption of its inorganic phosphorus byproducts. Results demonstrate that for initial DDVP concentrations below 5 mg L−1 (calculated as total phosphorus), both the mineralization rate under ultraviolet light irradiation with a wavelength of 365 nm and a power of 125 W and the adsorption rate of phosphorus were 100% when the pH was 6 and the UG 6:4 dosage was 0.2 g L−1. The sheet‐like g‐C3N4 tightly envelops the surface of UiO‐66, forming a Z‐scheme heterojunction. This structure imparts UG 6:4 with enhanced light absorption, faster generation and separation of photogenerated electron–hole pairs compared to individual UiO‐66 or g‐C3N4, and the establishment of an internal electric field suppresses the recombination of photogenerated charge carriers.CONCLUSIONConsequently, UG 6:4 exhibits outstanding photocatalytic pesticide removal capabilities. Furthermore, UG 6:4 demonstrates specific adsorption of inorganic phosphorus through electrostatic attraction and ligand exchange. This study indicates that UG 6:4 is a promising dual‐functional photocatalytic adsorbent with excellent application prospects. © 2024 Society of Chemical Industry (SCI).

Accelerating Small Electron Polaron Dissociation and Hole Transfer at Solid-Liquid Interface for Enhanced Heterogeneous Photoreaction.

In a photocatalysis process, quick charge recombination induced by small electron polarons in a photocatalyst and sluggish kinetics of hole transfer at the solid-liquid interface have greatly limited photocatalytic efficiency. Herein, we demonstrate hydrated transition metal ions as mediators that can simultaneously accelerate small electron polaron dissociation (via metal ion reduction) and hole transfer (through high-valence metal production) at the solid-liquid interface for improved photocatalytic pollutant degradation. Fe3+, by virtue of its excellent redox ability as a homogeneous mediator, enables the BiVO4 photocatalyst to achieve drastically increased photocatalytic degradation performance, up to 684 times that without Fe3+. The enhanced performance results from Fe(IV) species production (via Fe3+ oxidation) induced by dissociation of small electron polarons (via Fe3+ reduction), featuring an extremely low kinetic barrier (5.4 kJ mol-1) for oxygen atom transfer thanks to the donor-acceptor orbital interaction between Fe(IV) and organic pollutants. This work constructs a high-efficiency artificial photosynthetic system through synergistically eliminating electron localization and breaking hole transfer limitation at the solid-liquid interface for constructing high-efficiency artificial photosynthetic systems.

Graphdiyne‐Based Nickel–Cobalt Bimetallic Sulfide Cocatalyst for Efficient Photocatalytic Hydrogen Evolution

Initially, CoNiSx is synthesized on the graphdiyne (GDY) surface through a precipitation method, followed by the straightforward physical stirring approach to attach CoNiSx/GDY to the maple leaf CdS. This synthesis method significantly mitigates the accumulation of CoNiSx/GDY and concurrently augments the count of sites that are active for generating hydrogen. This three‐phase composite demonstrates exceptional performance in the area of photocatalytic hydrogen production, achieving a hydrogen evolution rate of 15.37 mmol·h−1 g−1. The employment of various characterization methodologies and density functional theory calculations have demonstrated the formation of a Z‐scheme heterojunction forms between GDY and CdS. This discovery indicates that the combination of GDY and CdS markedly improves the photogenerated carrier separation capability of the composite catalyst. The cocatalyst CoNiSx loaded on GDY effectively accelerates the electron transfer from the conduction band of GDY, thereby reducing the photogenerated carrier complexation of GDY. This phenomenon results in an increased quantity of photogenerated electron holes engaged in the redox reaction, ultimately achieving exceptional photocatalytic performance.

Effect of Vacancy Defects on the Electronic Structure and Optical Properties of Bi4O5Br2: First-Principles Calculations

First-principles calculations based on density functional theory are employed to investigate the impact of vacancy defects on the optoelectronic properties of Bi4O5Br2. The results indicate that vacancy defects induce minimal lattice distortion in Bi4O5Br2 without compromising its structural stability. Oxygen or bromine vacancies are more likely to occur than bismuth vacancies. The introduction of a bismuth vacancy leads to n-type semiconductor behavior in the Bi4O5Br2 system, while the creation of an oxygen vacancy reduces the bandgap and enhances the light absorption capacity. Bi4O5Br2 with three coordinated oxygen vacancies exhibits a higher effective electron–hole pair mass ratio, which is advantageous for the efficient separation of electron–hole pairs. Bi4O5Br2 with three coordinated oxygen vacancies exhibits enhanced absorption and reflection coefficients in the visible-light region compared to other systems, indicating that oxygen vacancy defects significantly promote visible-light absorption and electron–hole separation. This research provides new theoretical insights for understanding and optimizing the performance of photocatalysts based on Bi4O5Br2.

Development of Semi-Empirical and Machine Learning Models for Photoelectrochemical Cells

We introduce a theoretical model for the photocurrent-voltage (I-V) characteristics designed to elucidate the interfacial phenomena in photoelectrochemical cells (PECs). This model investigates the sources of voltage losses and the distribution of photocurrent across the semiconductor–electrolyte interface (SEI). It calculates the whole exchange current parameter to derive cell polarization data at the SEI and visualizes the potential drop across n-type cells. The I-V model’s simulation outcomes are utilized to distinguish between the impacts of bulk recombination and space charge region (SCR) recombination within semiconductor cells. Furthermore, we develop an advanced deep neural network model to analyze the electron–hole transfer dynamics using the I-V characteristic curve. The model’s robustness is evaluated and validated with real-time experimental data, demonstrating a high degree of concordance with observed results.

Defect Structure and Luminescence of κ‐Ga2O3 Micro‐Monocrystals

Wide bandgap orthorhombic polymorph of gallium oxide (κ‐Ga2O3) possessing a high spontaneous polarization grown on wurtzite‐type semiconducting substrates is considered to create a high mobility electron channel suitable for applications. Such κ‐Ga2O3 layers are composed of hexagon microprisms whose properties affect the lateral electric conductance. In this work, the structure and recombination properties of extended defects in individual “suspended” thin microprisms are investigated with transmission and scanning electron microscopy techniques (STEM, HR‐TEM) including cathodoluminescence (CL‐SEM). It is established that the microprism is composed of six equisized orthorhombic domains bounded by twin domain boundaries (TDBs) along the directions <110>. Twin domain contains a parallel array of antiphase boundaries (APB) of a high density stretched in the [010] direction. APBs possess steps or interruption and can form double oppositely shifted spatially separated layers (APB dipoles). TDBs on majority of their length are incoherent and serve as the border for the APB terminations. Panchromatic CL maps reveal either enhanced or reduced intensity of APB without noticeable spectral changes. CL intensity enhancement is proposed to be due to enhanced electron–hole generation caused by excess scattering of primary electron beam by APBs in thin films while, in fact, APB exhibits enhanced nonradiative recombination activity.

Incoherence-to-coherence crossover observed in charge-density-wave material 1T-TiSe2

Analogous to the condensation of Cooper pairs in superconductors, the Bose–Einstein condensation (BEC) of electron–hole pairs in semiconductors and semimetals leads to an emergence of an exotic ground state — the excitonic insulator state. In this paper, we study the electronic structure of 1T-TiSe2 utilizing angle-resolved photoemission spectroscopy and alkali-metal deposition. Alkali-metal adatoms are deposited in-situ on the sample surface, doping the system with electrons. The conduction bands of 1T-TiSe2 are thereby pushed down below the Fermi energy, which enables us to characterize its temperature dependence with precision. We found that the formation of the charge density wave (CDW) in 1T-TiSe2 at ~ 205 K is accompanied by a significant increase of the band gap, supporting the existence of excitonic pairing in the CDW state of 1T-TiSe2. More importantly, by analyzing the linewidth of the single-particle excitation spectrum, we unveiled an incoherence-to-coherence crossover at 165 K, which could be attributed to a possible exciton condensation that occurs beneath the CDW transition in 1T-TiSe2. Our results not only explain the exotic transport properties of 1T-TiSe2, but also highlight the possible existence of an excitonic condensate in this semiconducting material.

Enhanced performance of GaN based VCSELs through graded electron-blocking layer design

Electron leakage from the active region to the p-type region restricts the performance of GaN-based Vertical-Cavity Surface-Emitting Lasers (VCSELs). AlGaN EBL can decrease the leakage current, but also raises the hole injection barrier and reduce the hole injection efficiency. Then, it is important to design EBL structures that can enhance both electron blocking and hole injection. In this study, VCSEL devices with three different EBL, basic structure Al0.6Ga0.4N EBL labeled as Device A, newly proposed 16 nm thick Al0.75–0.80Ga0.25–0.20N EBL labeled as Device B, and 18 nm thick Al0.75–0.80Ga0.25–0.20N EBL labeled as Device C, respectively, are designed and analyzed using PICS 3D simulation. Device A represents a basic VCSEL structure, while Device C incorporates a graded electron-blocking layer (EBL) with adjusted thickness. Through simulation results, it is observed that the introduction of a graded EBL in Device C leads to significant performance enhancements compared to the basic structure of Device A. Specifically, the graded EBL effectively reduces band bending and increases the electron barrier height, thereby improving carrier confinement and reducing electron leakage. Additionally, the utilize of a Graded structure in Device C aids in strain relief at the layout between the QB and EBL, resulting in improved electron-blocking capability and potentially enhanced hole transport characteristics. These findings underscore the importance of EBL grading in optimizing the performance of VCSELs, highlighting its potential for advancing the efficiency and functionality of these semiconductor devices. Power of the device C is being improved upto 4.16%, similarly the conduction band barrier height is improved upto 26.6% which is beneficial for better VCSEL performance as it enhances electron confinement in the active region, leading to increased efficiency and reduced carrier leakage and valance band barrier height decreases upto 6.52% and threshold current is decreased upto 4.8% so if valence band barrier height decrease the hole injection efficiency increases and if threshold current decreases the emitting power of the device increase.

An inorganic lead-free Cs2SnI6-based perovskite solar cell optimization by SCAPS-1D

Cs2SnI6 is an environmentally friendly and reliable perovskite solar cell (PSCs) material. Its optimal band gap and strong light absorption make it a promising candidate for the absorption layer. However, the current challenge is to improve its photoelectric conversion efficiency. To address this, this study investigates the performance of PSCs based on Cs2SnI6 using SCAPS-1D simulation. The influence of various factors on PSC performance is examined, including different hole transport layers(HTLs) and electron transport layers(ETLs), perovskite layer thickness, ETL doping density, HTL doping density, absorber doping density, perovskite layer defect density, different back contacts and temperature. Finally, a Cs2SnI6-based solar device with an inorganic configuration of FTO/NiO/Cs2SnI6/SnO2/Au has been developed, reaching the power conversion efficiency(PCE) of 28.69 %. The study demonstrates that Cs2SnI6 PSCs exhibit promising photovoltaic performance, offering valuable insights for the solar energy sector in the production of cost-effective, efficient, and environmentally friendly Cs-based perovskite solar cells.

Fast electron initiated electron–hole pair creation in semiconductors

Through Monte Carlo modeling, it is shown that the statistics of electron–hole pair creation in semiconductors (and by extension, presumably, ion-pair creation in gas proportional counters) are substantially different for fast electrons (and by extension, presumably, alpha particles, ions, etc.) cf. x-ray/γ-ray photons. New variables are introduced to quantify the differences in the statistics: the loss parameter, ζ(E′), which acts on the average e−–h+ pair creation energy; and the broadening factor, B(E′), which acts on the Fano factor. E′ is the initial energy of the fast electron. ζ(E′) and B(E′) are computed for a variety of semiconductor materials. A new equation for the statistically limited energy resolution of a particle counting fast electron spectrometer is established. This new equation supersedes and replaces that for the Fano-limited energy resolution of a particle counting fast electron spectrometer. The implications impact a wide variety of fields wherever fast electrons (or alpha particles, ions, etc.) and/or Fano statistics are used; this includes, inter alia, quantum computing, x-ray excitonics, space science, optoelectronics, nuclear engineering, particle physics, photovoltaics, and even neural response variability in the brain.

Construction of pyrrolo[3,2-b]pyrrolyl-linked covalent organic polymers to promote continuous overall H2O2 production

Sacrificial agent-free, solar-driven photocatalytic oxygen reduction holds promise for hydrogen peroxide production. However, the rapid recombination of electron–hole pairs in catalysts and the slow diffusion rate of oxygen on the catalyst surfaces significantly hinder the efficiency of hydrogen peroxide production. To address these issues, we developed a novel class of pyrrolo[3,2-b]pyrrolyl-linked covalent organic polymers (COPs) combined with microreactor technology to enhance hydrogen peroxide synthesis. These structurally well-defined polymers feature photoactive pyrrolo[3,2-b]pyrrolyl units were assembled from aldehyde, aniline, and 2,3-butanedione through a one-pot three-component reaction. Integrating pyrrolo[3,2-b]pyrrolyl moieties into the COPs creates donor–acceptor structures that facilitate the separation of photogenerated electrons and holes. Among them, COP-2 achieved the highest H2O2 yield of 5446 μmol g−1 h−1. Furthermore, we designed a coiled tube photomicroreactor to improve mass transfer efficiency in the gas–liquid–solid triphase system, boosting the H2O2 yield to 20285 μmol g−1h−1 without the need for a sacrificial agent. This study offers new insights into integrating polymer photocatalysts with microflow technology, underscoring the potential for future green and continuous H2O2 production.

A study of optical properties and electron energy loss spectra of ZnS by linear response theory

The linear response theory has been applied to study the optical properties and electron energy loss spectra of ZnS. The ground state is built using the Full-Potential Linearized Augmented Plane Wave method. Thereafter, the electronic properties such as band structure and density of states are calculated. Calculations of electron energy loss spectra and optical properties are performed on the top of these ground state electronic properties. The calculations are performed using three exchange–correlation kernels namely, adiabatic local density approximation, long range contribution, and the bootstrap. The random phase approximation is also considered. An approach proposed by us to find the material dependent parameter α is used in long range contribution kernel to capture more accurate optical properties. Three values of α viz 0.78, 1.09, and 1.22 are considered. It is observed that the α = 0.78 gives very good results. This proposed scheme is found to work very well for ZnS also. The effect of local field and electron–hole interaction on the spectra is examined. For example after incorporating local field effect the high frequency dielectric constant ε∞ [i.e. ε1E→0eV ], reduces by 9.19, 12.26, 13.51 and 11.02% for random phase approximation, adiabatic local density approximation, long range contribution and bootstrap kernel respectively. In EELS plasmon peak positions are found using the three kernels and random phase approximation. A good accord with experimental results is noted after incorporating local field effects. It is observed that local field effect causes redshift of prominent peak (i.e. plasmon peak) in electron energy loss spectra by 0.61 eV.

A Photo-Assisted Zinc-Air Battery with MoS2/Oxygen Vacancies Rich TiO2 Heterojunction Photocathode.

Converting solar energy into electrochemical energy is a sustainable strategy, but the design of photo-assisted zinc-air battery (ZAB) with efficient utilization of sunlight faces huge challenges. Herein, a photo-assisted ZAB of a three-electrode system using MoS2/oxygen vacancies-rich TiO2 heterojunction as charge cathode and Fe, N-doped carbon matrix (FeNC) as discharge cathode is constructed, where MoS2 is chosen as solar light-responsive catalytic material and TiO2 acts as electron transport layer and hole blocking layer, arising from a train of thought for efficient charging under sunlight irradiation and light-independent discharging. The introduction of oxygen vacancies in TiO2 facilitates the temporary trapping of carriers and triggers rapid carrier transfer at the interface of the heterojunction, which hinders the recombination of photogenerated holes, thereby facilitating their further participation in the oxygen evolution reaction. Moreover, FeNC exhibits superior oxygen reduction reaction performance due to strong d-π interactions. As a result, the well-built ZABs deliver a low charge voltage (0.71 V) under illumination at 0.1 mA cm-2, and a high power density (167.6mW cm-2) in dark. This work paves a special way for the development of ZABs by directly harvesting solar energy in charging and efficiently discharging regardless of lighting conditions.

Multifunctional optoelectronic devices based on two-dimensional tellurium/MoS2 heterojunction

Two-dimensional van der Waals heterojunctions consisted of p–n-type semiconductors have been rapidly developed owing to their built-in electric field which can facilitate the separation of photogenerated electron–hole pairs and properties like current rectification and negative differential transconductance. Benefitting from these advantages, we have prepared an air-stable multifunctional p-tellurium (Te)/n-MoS2 heterostructure working both as a self-driven broadband photodetector and as an optically switchable complementary metal-oxide-semiconductor inverter. For photodetection, this device exhibits wavelength-modulated positive/negative optical response with large responsivity (1.51 A/W at 520 nm and 642.92 mA/W at 1550 nm, Vds = 0 V) and fast response speed, showcasing its prospects for optical encoding communication. Moreover, the device has been demonstrated to function as an inverter that will be shut down by illumination. Our multifunctional device possesses the compactness of integrated modules, widens the application scope of Te-based heterojunctions, and provides a reference for the application of Te-based devices in the field of integrated circuits.

A 326 nm pure ultraviolet light sources achieved in a Ga[formula omitted]O[formula omitted] microwire heterojunction through interface optimization and surface-modification

Low-dimensional Ga2O3 single-crystals have caused widespread attentions in the potential of developing ultraviolet light sources due to its ultrabroad bandgap, low-budget, high thermally stable, high breakdown voltage and others. Herein, we exhibit a significant route to construct one-dimensional Ga2O3 microwire heterojunction deep-ultraviolet light-emitting diode (LED). The resulting electroluminescence is positioned at 326 nm with a narrow linewidth of about 22.5 nm, which is the shortest wavelengths once published for the Ga2O3-related light sources. In the well-fabricated LED, an intermediate AlN layer enables appropriately to manipulate band alignment of n-Ga2O3/p-GaN heterojunction, thus achieving efficient confinement of electron–holes spreading and radiative recombination within the Ga2O3 microwire active medium. Benefited from surface-modified Pt nanoparticles, the LED’s electroluminescence efficiency and brightness can be plasmonically boosted. More importantly, the peak energy at 3.8 eV obtained under forward bias, which is smaller than the Ga2O3 bandgap, could be resulted from radiative recombination of weakly-bounded electron–holes inside the Ga2O3 microwires. Therefore, the Ga2O3 monocrystalline wires synthesized using high-temperature carbothermal reduction, are expected as promising-looking candidates to develop environmentally friendly, easy miniaturization, highly-stable deep-ultraviolet light sources and photonic devices.

Investigating the Impact of Stress on the Optical Properties of GaN-MX2 (M=Mo, W; X=S, Se) Heterojunctions Using the First Principles

This study used the first-principles-based CASTEP software to calculate the structural, electronic, and optical properties of heterojunctions based on single-layer GaN. GaN-MX2 exhibited minimal lattice mismatches, typically less than 3.5%, thereby ensuring lattice coherence. Notably, GaN-MoSe2 had the lowest binding energy, signifying its superior stability among the variants. When compared to single-layer GaN, which has an indirect band gap, all four heterojunctions displayed a smaller direct band gap. These heterojunctions were classified as type II. GaN-MoS2 and GaN-MoSe2 possessed relatively larger interface potential differences, hinting at stronger built-in electric fields. This resulted in an enhanced electron–hole separation ability. GaN-MoSe2 exhibited the highest value for the real part of the dielectric function. This suggests a superior electronic polarization capability under an electric field, leading to high electron mobility. GaN-MoSe2 possessed the strongest optical absorption capacity. Consequently, GaN-MoSe2 was inferred to possess the strongest photocatalytic capability. The band structure and optical properties of GaN-MoSe2 under applied pressure were further calculated. The findings revealed that stress significantly influenced the band gap width and light absorption capacity of GaN-MoSe2. Specifically, under a pressure of 5 GPa, GaN-MoSe2 demonstrated a significantly narrower band gap and enhanced absorption capacity compared to its intrinsic state. These results imply that the application of stress could potentially boost its photocatalytic performance, making it a promising candidate for various applications.