Gallium oxide has emerged as a prominent ultrawide bandgap semiconductor material. Its outstanding physical properties， including a bandgap of approximately 4.9 eV and a breakdown electric field strength of 8 MV/cm， combined with the unique capability of producing large-size single crystal substrates via melt growth methods， have positioned it at the forefront of research on the high-power electronic devices， radio-frequency front-end devices， and solar-blind ultraviolet photodetection. In recent years， substantial advances has been made in substrate preparation， epitaxial growth， and device processing. Epitaxial films serve as a critical bridge between substrates and devices， whose quality directly determines the performance limits of the final devices. Doping control and defect management during epitaxial growth are considered a core challenge in the field. This review provides a systematic overview of the research status and development trends of β-Ga₂O₃ epitaxial films. It begins by introducing the research background， crystal structure， and fundamental physical properties of gallium oxide. This review then provides a detailed assessment of progress in major epitaxial growth techniques， including hydride vapor phase epitaxy， metalorganic chemical vapor deposition， and molecular beam epitaxy， with emphasis on key strategies such as the suppression of background carrier concentration， precise control of n-type doping， high-rate growth of thick films， and inhibition of defects. The significant challenge of achieving p-type doping is analyzed， and its physical mechanisms along with the latest research developments are summarized. Furthermore， recent achievements in the heteroepitaxy of β-Ga₂O₃， α-Ga₂O₃ and ε-Ga₂O₃ are summarized. Finally， based on current technical bottlenecks and future application requirements， prospects for the development of gallium oxide epitaxial technology are presented， with the aim of providing a useful reference for both fundamental research and industrial applications in this field.

Diamond possesses exceptional physical and chemical properties， making it a critical material in thermal， optical， mechanical， and electrical applications. However， the scarcity of natural diamond and the limitations of high-pressure high-temperature （HPHT） methods in producing large-area films have driven the search for alternative synthesis techniques. Since the mid-20th century， chemical vapor deposition （CVD） has emerged as a leading method. Among various CVD approaches， microwave plasma chemical vapor deposition （MPCVD） is highly regarded for its high growth quality， high plasma density， absence of electrode contamination， and stable deposition parameters. This review focuses on the significant advancements and potential of lower-frequency （915 MHz） MPCVD technology for synthesizing large-area， high-quality diamond films， addressing its unique mechanisms， current technological status， and future directions. The primary objective of this work is to provide a systematic and detailed review of 915 MHz MPCVD technology， encompassing theoretical simulations， reactor design， deposition processes， and applications. It aims to elucidate the fundamental advantages of the lower frequency， analyze the design evolution and performance of various 915 MHz reactor configurations， summarize the effects of key process parameters on film characteristics， and outline prevailing challenges and future trends. The core innovation and academic value of this review lie in its comprehensive synthesis of scattered research， highlighting how the shift from 2.45 GHz to 915 MHz is not merely a scaling exercise but introduces fundamental changes in plasma physics and chemistry that are conducive to large-scale， low-defect diamond synthesis. The methodology of this review involves a critical analysis of extensive published literature and experimental reports. It examines the theoretical underpinnings， including electromagnetic field simulations and plasma modeling specific to 915 MHz systems. The review categorizes and compares mainstream reactor designs such as ellipsoidal cavities， ring-antenna coupled systems， and slit-coupled configurations—based on their microwave coupling mechanisms， electric field distributions， plasma uniformity， and operational reliability. Furthermore， it synthesizes experimental data on how key process parameters （microwave power， chamber pressure， substrate temperature， gas composition， and flow dynamics） influence the growth rate， quality， uniformity， and stress of deposited diamond films， including single-crystal （SCD）， microcrystalline （MCD）， and nanocrystalline （NCD） diamond. The results indicate that 915 MHz MPCVD offers distinct advantages over its 2.45 GHz counterpart. The longer wavelength allows for the generation of a larger and more uniform plasma volume， which is fundamental for depositing diamond films on substrates with diameters exceeding 150 mm， with reports of up to 200 mm. The plasma characteristics at 915 MHz， featuring a longer plasma sheath， a modified electron energy distribution function （EEDF）， and gentler ion bombardment energy at the substrate， contribute to reduced intrinsic film stress and lower defect density. This is particularly promising for growing semiconductor-grade single-crystal diamond. Simulations and experiments confirm that optimized reactor geometries and precise tuning can effectively focus microwave energy， suppress secondary plasmas， and enhance process stability. Institutions and companies worldwide have demonstrated the production of high-quality， crack-free， free-standing diamond wafers using 915 MHz systems with powers ranging from 20 kW to over 75 kW. In conclusion， 915 MHz MPCVD represents a pivotal technological pathway for the industrial-scale synthesis of large-area， high-performance diamond films. Its inherent advantages in plasma stability and film quality control address critical bottlenecks in traditional methods. However， key challenges remain， including the development of high-power， stable solid-state microwave sources， advanced reactor designs for improved sealing and heat management， and a deeper quantitative understanding of the plasma-chemistry-film property relationships. Future progress hinges on multi-physics coupled simulations， intelligent process control with real-time diagnostics， and breakthroughs in heteroepitaxial integration for large-area single-crystal diamond substrates. Mastering this technology from fundamental mechanisms to engineering integration will be crucial to unlocking diamond's full potential in next-generation high-power electronics， quantum information science， and extreme optical applications.

Rare earth silicates RE₂SiO₅ （RE=rare earth） with significant applications as laser host， scintillator， thermal barrier coatings， and quantum memory devices， generally exhibit two distinct structural phases： X1-type （lower temperature， space group P2₁/c） and X2-type （higher temperature， space group C2/c）. Each structure contains two unique sites hosting the rare earth ions， characterized by different coordination numbers （CNs）. Theoretical calculations with the electronic structure and molecular dynamics software package CP2K were performed to better understand the structural stabilities of these compounds and the preferential site occupations of doping rare earth ions. The Gaussian basis set and the Perdew-Burke-Ernzerhof for solids （PBEsol） functional were employed due to their high computation speed and their reliable structural optimization results for solid materials. According to the results from theoretical calculations， it is found that the dispersion correction plays a vital role in correctly predicting the relative structural stability of the RE₂SiO₅ phases. Furthermore， the doping behaviors of rare earth ions with varying sizes in Y₂SiO₅ are systematically investigated. Our findings reveal that in both phases， Y1 site （CN=9 for X1-type， and CN=7 for X2-type） is preferentially occupied by larger ions like La³⁺， while smaller ions such as Sc³⁺ demonstrate greater stability at Y2 site （CN=7 for X1-type， and CN=6 for X2-type）. These results provide valuable insights into the structural properties and doping mechanisms of this class of crystals.

High-temperature piezoelectric sensors are critically needed in extreme-environment applications such as aerospace， nuclear energy， and industrial process monitoring. Traditional piezoelectric ceramics and polymers often exhibit significant performance degradation under high-temperature and low-oxygen conditions. Among emerging high-temperature piezoelectric single crystals， langasite-family crystals， particularly the structurally ordered Ca₃TaGa₃Si₂O₁₄ （CTGS） have attracted considerable attention due to their high resistivity， absence of phase transitions up to their melting point （>1 400 ℃）， and suitability for large-size growth via the Czochralski method. However， further enhancement of their electromechanical properties and thermal stability is essential to meet the demands of advanced sensor applications. This study aims to optimize the high-temperature electromechanical properties of CTGS crystals through lattice substitutions. Two distinct substitution strategies were employed： Sr substitution at the A-site （Ca site） to form （Sr _x Ca_1-x ）₃TaGa₃Si₂O₁₄ （SCTGS）， and Al substitution at the C-site （Ga site） to form Ca₃Ta（Ga _x Al_1-x ）₃Si₂O₁₄ （CTGAS）. Crystals with varying substitution ratios （x=0.25， 0.50 for Sr； x=0.30， 0.50 for Al） were grown by the Czochralski method under N₂ atmosphere using iridium crucibles. The crystalline quality was evaluated by high-resolution X-ray diffraction rocking curves， showing full-width half-maximum values between 33.41″ and 58.73″， which confirmed good crystallinity. Resistivity was measured from 350 ℃ to 800 ℃ along the crystallographic Y- and Z-directions. Results indicate that the Al substitution significantly increases the high-temperature resistivity， with 50%CTGAS reaching approximately 1×10⁷ Ω·cm at 800 ℃ along the Z-direction. In contrast， Sr substitution reduces resistivity， with 50%SCTGS exhibiting ~1×10⁵ Ω·cm under the same conditions. Dielectric and piezoelectric properties were systematically characterized from room temperature to 800 ℃ using specifically designed crystal cuts （X-cut， Z-cut， XYt/0°， and YZt/45°）. Results indicate that the Sr substitution notably enhances the room-temperature piezoelectric coefficients： d₁₁ and d₁₄ reaches 4.84 and -20.17 pC/N for 50%SCTGS， representing increases of 16.1% and 81.2%， respectively， over pure CTGS. The relative dielectric permittivity {\epsilon }_{\mathrm{11}}^T/{\epsilon }_{\mathrm{0}} also increases with the increase of Sr content. In contrast， Al-substituted crystals retaines piezoelectric coefficients similar to pure CTGS while markedly improving thermal stability. The variation in piezoelectric coefficient d₁₁ is less than 10.5% across 25~800 ℃， and dielectric loss remained below 0.2 up to 600 ℃. To elucidate the mechanisms， bond-valence-based calculations of polyhedral dipole moments were performed. Results indicate that the large dipole moment of the ［SrO₈］ polyhedron （12.204 5 D） in SCTGS accounts for its enhanced piezoelectric response， whereas the reduces dipole moment in ［CaO₈］ and improves structural order upon Al substitution explain the superior resistivity and thermal stability of CTGAS. In conclusion， Sr substitution could effectively enhance the piezoelectric activity of CTGS crystals， while Al substitution could significantly improve high-temperature resistivity and electromechanical stability. This work demonstrates that site-specific substituting is a powerful strategy for tailoring CTGS-based materials toward specific high-temperature sensor requirements.

The two-dimensional acousto-optic Q-switch is a key component in laser Q-switching systems. Traditional devices based on a right-angle triangular prism geometry suffer from inherent drawbacks， including return acoustic wave interference， diffraction spot distortion， stepped distortion in the modulation waveform， and a complex three-sided water-cooling structure. This work proposes a new geometric structure for a two-dimensional acousto-optic Q-switch to fundamentally eliminate return acoustic wave interference， simplify thermal management， and achieve high diffraction efficiency with clean modulation waveforms， while maintaining compactness and reliability for high-power laser applications. In this paper， a fused silica acousto-optic crystal with a non-symmetrical wedge geometry was designed. Unlike the conventional right-angle prism， the new geometry structure ensured that after the first orthogonal acousto-optic interaction of the acoustic wave， the reflected acoustic paths were spatially offset from the main working region， thereby avoiding return wave interference. Two orthogonal y-36° LiNbO₃ transducers were bonded onto the crystal， with a center frequency of 27.12 MHz and an operating wavelength of 1 064 nm. The effective aperture is 3 mm×3 mm （rectangular） and the acousto-optic interaction length was 42 mm. The water-cooling structure was simplified from three-sided water-cooling structure to two main water-cooling blocks， reducing assembly complexity. Experimental results show that with dual-channel radio frequency （RF） drive power of 47 W per channel， the two-dimensional diffraction efficiency reaches 98.5%， and the diffraction spot pattern exhibits a regular grid distribution without distortion. The modulation waveform shows a steep rising edge （~307.7 ns） and falling edge （~774.8 ns） with a flat top， free from the stepped distortion observed in conventional devices. The impedance curve at 27.12 MHz is smooth and close to 50.2 Ω， matching standard RF systems. Thermal imaging reveals a steady-state crystal temperature of approximately 69.7 ℃ under dual-channel RF drive power of 47 W per channel （compared to 54.4 ℃ for the conventional design）， which is well below the softening point of fused silica. A 4 h continuous aging test confirms excellent thermal stability. The temperature stabilizes at （71±1） ℃， the diffraction efficiency remains between 97.5% and 98.7% （standard deviation ~0.28）， and the modulation waveform shows no degradation. In this paper， the proposed two-dimensional acousto-optic Q-switch with new geometric structure successfully eliminates return acoustic wave interference through spatial path control， providing a universal design approach applicable to other acousto-optic materials （e.g.， TeO₂， SiO₂， Ge） for different laser wavelengths. Although the new geometry structure imposes slightly higher precision requirements on crystal fabrication， the simplified two water-cooling block structure reduces overall assembly cost and complexity， while maintaining high performance and long-term reliability. This work offers a practical and innovative pathway for developing advanced acousto-optic devices.

This paper introduces an acousto-optic modulator （AOM） featuring high diffraction efficiency and a large aperture. The AOM is designed for operation at 1 064 nm， with an effective aperture of 10 mm and a center operating frequency of 80 MHz. Low-absorption quartz was selected as the acousto-optic medium， while high-efficiency lithium niobate served as the piezoelectric transducer. Through optimized design and bonding processes， combined with a heat-conductive and electrically conductive heat dissipation solution utilizing a pressure block and adhesive pad， a diffraction efficiency of 98.4% was achieved. This AOM simultaneously exhibits excellent outstanding beam quality and high beam pointing stability. The research provides a critical high-performance optical component for high-power laser applications.

Commercial gallium nitride （GaN） devices are typically fabricated on heterogeneous GaN epi-wafers. However， cutting-edge research continues to focus on the development of homoepitaxial devices based on free-standing GaN single crystal substrates， aiming to leverage the superior material properties of homoepitaxy to further enhance device performance. Among the emerging technologies for manufacturing such GaN substrates， the sodium flux method is promising due to its capability to produce large， stress-free， high-quality crystals. A significant challenge is the separation of the thick GaN layer from the original sapphire substrate. Previous work by Japan Osaka University introduced a lithium-doped flux method involving a two-step process with a Li concentration of ~10% （mole fraction， the same below）， requiring a complex reactor design. This study presents a significant simplification of this approach. The primary goal of this study is to demonstrate and investigate a simplified， single-step sodium flux method for the epitaxial growth of a thick， crack-free GaN single crystal on a sapphire-based template， achieving complete self-separation of the grown layer from the sapphire substrate. A GaN template （~30 μm thick） was first prepared on a sapphire substrate using metalorganic chemical vapor deposition and hydride vapor phase epitaxy （HVPE）. This template served as the seed. Epitaxial growth was conducted in a high-pressure autoclave using a sodium flux with a molar composition of n（Na）∶n（Ga）∶n（C）∶n（Li）=73.0∶27.0∶0.5∶0.3， corresponding to a very low Li concentration of approximately 0.3%. The growth proceeded at 850 ℃ and 3.5 MPa under a nitrogen atmosphere for 120 h. The morphology， crystallinity， surface roughness and structural changes of the separated GaN layer and sapphire substrate were analyzed by optical microscopy， X-ray diffraction， atomic force microscopy and thickness measurement. The curved wafer was measured before and after growth to evaluate stress evolution. A crack-free， mirror-like GaN single crystal layer with an average thickness of 1 053 μm is successfully grown. Crucially， the GaN epilayer completely and spontaneously separates from the sapphire substrate upon cooling. The separation interface is located precisely at the original GaN/sapphire boundary. The sapphire substrate shows clear etching features， with its thickness reduces by ~10 μm and sidewall/edge etching observed. In contrast， the separated surface of the GaN layer is smooth （root mean square roughness is 3.04 nm） with no signs of etching， indicating highly selective etching of sapphire. The GaN surface exhibits millimeter-scale hexagonal hillocks. Bowing measurements reveals that the initial convex bow of the template （due to thermal stress from HVPE growth） transformed into a concave bow of the free-standing GaN layer after growth and separation， indicating significant stress relaxation. This work successfully demonstrates a novel， simplified sodium flux process using a trace amount of lithium （0.3%） to achieve simultaneous epitaxial growth and complete self-separation of a millimeter-thick GaN single crystal from its sapphire substrate in a single step. The self-separation mechanism is attributed to the synergistic effect of the slow， selective etching of the sapphire substrate by the Li-doped flux and the progressive accumulation and release of interfacial stresses during crystal growth. The key innovation of this paper is to significantly reduce the required Li concentration by an order of magnitude （from ~10% to 0.3%） while maintaining the self-separation functionality， eliminating the need for a complex two-step process or high-pressure mechanical additions. This study provides fundamental insights into the stress-mediated， flux-assisted liftoff mechanism and proposes a markedly simplified and more cost-effective technical route for the sodium-flux-based fabrication of large， free-standing GaN substrates， potentially accelerating their commercialization for next-generation high-power and high-frequency electronic devices.

Gallium oxide （β-Ga₂O₃） is endowed with broad application prospects in the field of power devices， as it possesses a wide bandgap， a high critical breakdown electric field， and low-cost substrates. However， the development of β-Ga₂O₃ homojunction Schottky barrier diodes （SBD） is restricted by the bottleneck of P-type doping technology. To address this issue， a P-NiO/β-Ga₂O₃ heterojunction SBD structure was proposed， in which P-NiO was used to replace P-type β-Ga₂O₃.The effects of P-NiO doping concentration， P-NiO thickness （W）， and anode length （L_a） on the electrical properties of devices were studied by means of Sentaurus TCAD software. The results show that the increase of P-NiO doping concentration leads to the expansion of the depletion region to the side of the β-Ga₂O₃ material， resulting in the improvement of the uniformity of the electric field distribution. When the P-NiO doping concentration is 3×10¹⁸ cm^-3， the performance is the best. At this time， the specific on-resistance （R_on，sp） is 1.411 mΩ·cm²， the reverse breakdown voltage is 3 312.2 V， and the power figure of merit （PFOM） is 7.77 GW/cm². L_a and W are further optimized to alleviate the edge electric field concentration effect. Finally， the R_on，sp of the device reduces to 0.823 mΩ·cm²， the reverse breakdown voltage increases to 3 638.3 V， and the PFOM reaches 16.08 GW/cm². The structure of this paper provides a theoretical basis for the design and development of high performance β-Ga₂O₃ SBD.

The minority carrier lifetime of silicon wafers generally decays sharply after high-temperature processes in solar cell fabrication， significantly limiting further improvements in cell efficiency. To elucidate the underlying mechanism， this study systematically investigated the high-temperature behavior of photovoltaic-grade n-type Czochralski （Cz） silicon wafers through controlled heat treatment experiments， combined with multi-scale characterization techniques including minority carrier lifetime， photoluminescence（PL）， and Fourier-transform infrared spectroscopy. The results demonstrate that the significant degradation in both minority carrier lifetime and PL intensity after high-temperature treatment primarily stems from a substantial increase in bulk recombination defects， with surface conditions and process atmosphere playing a minor role. Furthermore， during heat treatment， interstitial oxygen within the silicon wafer converts into precipitated oxygen， accompanied by net inward diffusion of ambient oxygen in an oxygen-rich atmosphere. Comprehensive analysis indicates that oxygen precipitate nuclei pre-existing in the as-grown silicon wafers become activated and grow during high-temperature process， forming oxygen precipitates with high recombination activity， which is identified as the main cause of minority carrier lifetime degradation. Based on the mechanism of ‘selective activation and growth of oxygen precipitate nuclei’， this study proposes two optimization strategies： suppressing nucleus formation by optimizing the crystal cooling thermal history and eliminating existing defects through rapid thermal annealing.

Antimony selenide （Sb₂Se₃） is a promising photovoltaic thin-film material， owing to its abundant reserves， non-toxicity， and good stability. Despite substantial advances in its power conversion efficiency， the underlying carrier transport mechanism—particularly the key scattering processes that limit the hole mobility—remains unclear. To address this， first-principles density functional theory （DFT） combined with Boltzmann transport theory was used to quantitatively evaluate the contributions of acoustic deformation potential （ADP）， ionized impurity （IMP）， and polar optical phonon （POP） scattering to Sb₂Se₃ hole mobility. The calculated room-temperature hole mobility is 42.8 cm²·V^-1·s^-1. The results show that POP scattering dominated the limitation of hole mobility over a temperature range of 105~650 K. The mobility exhibits distinct anisotropy along the three principal crystallographic directions （x， y and z）， with the highest mobility in the y-axis direction and the lowest in the z-axis direction. It is also found that at low carrier concentrations， the hole mobility remains essentially unchanged as carrier concentration increases； at high carrier concentrations， the hole mobility decreases as carrier concentration increases. This work clarifies the dominant factors restricting the hole mobility of Sb₂Se₃ and offers a theoretical foundation for further performance optimization.

In this paper， NASICON-type sodium-ion solid electrolyte Na₃Sc₂（PO₄）₃ was synthesized by solid-state reaction method using scandium oxide， sodium carbonate and ammonium dihydrogen phosphate as raw materials. The effects of scandium oxide content on sintering properties， phase composition， microstructure and ionic conductivity were studied. The electrolytes were characterized using X-ray diffraction （XRD）， scanning electron microscopy （SEM）， and electrochemical performance was tested by electrochemical impedance spectroscopy （EIS）. The results indicate that a proportional NASICON-type Na₃Sc₂（PO₄）₃ is obtained when the scandium oxide content is 21.49% （mass fraction）， at which the synthesized materials exhibits a dense microstructure， high crystallinity， uniform grain size， and the largest unit cell volume. Consequently， it demonstrates the highest room-temperature ionic conductivity of 8.79×10^-6 S/cm. An excess of scandium oxide inhibites grain growth and forms the sodium-deficient Na_2.63Sc₂（PO₄）₃ phase. The sodium vacancies increase， the lattice distortion occurs， the porosity increases， and the ionic conductivity decreases. The lack of scandium oxide causes cell shrinkage and glass phase covering grain boundaries， hindering ion migration， which is also not conducive to ion transport and reducing ion conductivity. Therefore， precise stoichiometric control is critical for optimizing the structure and enhancing the ionic conductivity of NASICON-type Na₃Sc₂（PO₄）₃ electrolytes.

This study developed a green method for preparing cuprous oxide （Cu₂O） nanoparticles using extracts from the stems and leaves of Dipsacus asper wall. The optical properties， microstructure， and phase composition of the prepared samples were characterized by analytical techniques such as UV-Vis， Raman， XRD， TEM， SEM， EDX， and XPS， and their antibacterial activity was also tested. The results show that the Cu₂O nanoparticles prepared using Dipsacus asper wall stem and leaf extracts as the reducing agent are cubic system with space group of Pn3m， exhibiting good crystallinity and high purity. Their microscopic morphology reveals a unique three-dimensional “cauliflower-like” structure， with an atomic ratio of Cu to O approximately 2.12∶1 in elemental composition. UV-Vis spectrum shows the characteristic surface plasmon resonance （SPR） absorption peak of Cu₂O at 565 nm. Antibacterial tests indicate that the Cu₂O nanoparticles exhibit significant inhibitory effects against escherichia coli， staphylococcus aureus， bacillus subtilis， and pseudomonas aeruginosa， with minimum inhibitory concentrations of 1.000， 0.125， 0.125， and 0.250 mg/mL， respectively. The study not only provides a novel and eco-friendly strategy for the preparation of Cu₂O nanomaterials but also demonstrates their potential applications in the field of antibacterial treatment.