Infrared lasers in the 1-3 μm region are increasingly important for applications in medical treatment, atmospheric monitoring, and high-power laser systems. Holmium ions (Ho³⁺) are particularly attractive because of their multiple emission channels covering near to mid infrared ranges. This work aims to systematically evaluate the structural and spectroscopic properties of Ho:BaF₂ crystals and determine the optimal doping concentrations for efficient multi-band laser operation. High-quality Ho:BaF₂ single crystals with concentrations of 0.5%-3.0% (in atom) were grown using the temperature gradient technique (TGT). Structural characterization was performed, while spectroscopic properties were analyzed via absorption, fluorescence, and lifetime measurements. Judd-Ofelt analysis was further applied to calculate radiative parameters. All samples exhibited cubic structures, with doping segregation ratios close to unity and uniform Ho³⁺ distribution. Spectroscopic evaluation revealed optimal doping concentrations of 2.0% (in atom) for ~1.2 μm (⁵I₆→⁵I₈, spectral quality factor Q=24.29×10^-21 cm²·ms) and ~2.05 μm (⁵I₇→⁵I₈, Q=67.53×10^-21 cm²·ms), and 1.0% (in atom) for ~2.85 μm (⁵I₆→⁵I₇, Q=44.52×10^-21 cm²·ms). BaF₂ host, with its low phonon energy (~346 cm^-1) and anti-clustering characteristics, enabled enhanced emission performance, including a maximum emission cross-section of 3.81×10^-21 cm² at ~2.05 μm. These results outperform traditional hosts such as YAG and CaF₂. Compared to oxide hosts, BaF₂ offers superior lifetime, reduced non-radiative losses, and greater resistance to concentration quenching. The findings indicate that Ho:BaF₂ supports higher effective doping levels, making it particularly promising for high-power and ultrafast laser applications. Ho:BaF₂ crystals demonstrate excellent potential as efficient, multi-wavelength infrared laser gain media.

Indium selenide (InSe), a typical layered III-VI semiconductor, has attracted intense interest owing to its high electron mobility, tunable bandgap and exceptional plastic deformation capability, enabling it a promising candidate for next-generation electronic, optoelectronic and flexible devices. Recently, the controlled growth of intrinsic InSe crystals has been well developed, whereas doping InSe crystals with a third element remains relatively scarce. In this study, intrinsic InSe crystals were grown using the Bridgman method, and high-quality Bi-doped InSe crystals were then prepared through introducing Bi during the crystal synthesis stage. Optical microscopy and scanning electron microscopy observations indicate that the as-grown Bi-doped InSe crystals exhibit a smooth surface and excellent single-crystalline characteristic. Raman spectroscopy and X-ray diffraction analyses further demonstrate that, after Bi doping, their phase structure is consistent with former intrinsic crystals, exhibiting ε-InSe phase. Chemical etching experiments reveal that the doped Bi atoms can interact with dislocation cores within the crystal, effectively suppressing their motion and significantly reducing their dislocation density. Electrical measurements show that the Bi doping markedly increases carrier concentration and mobility of InSe crystal at high temperature, which is primarily attributed to the introduction of additional free carriers and suppression of carrier scattering resulting from the reduced dislocation density. Consequently, Bi-doped InSe crystal was successfully fabricated, and its superior performance compared to the intrinsic InSe was verified. This work provides theoretical insights and experimental guidance for optimizing properties of InSe crystals in application in future devices.

KTb₃F₁₀ (KTF) crystal, characterized by its high Tb³⁺ ion concentration, low thermo-optic coefficient and low phonon energy, exhibits significant potential for efficient laser emission in the green and yellow wavelength ranges. However, challenges such as incongruent melting behavior, hygroscopicity of raw materials, high-temperature compositional volatility, and corrosive nature of fluorides have severely hindered the growth of high-quality KTF crystals. This study aims to develop an effective approach to address these issues, achieve the growth of high-quality KTF crystals, and characterize their optical properties. An optimized vertical Bridgman method integrated with a laser-sealed platinum crucible technique under vacuum was employed. This innovative approach effectively shielded the raw materials from water and oxygen contamination while suppressing compositional deviation during crystal growth through a sealed environment. As a result, blank KTF crystals with dimensions of φ16 mm×30 mm were successfully grown, and their relevant spectral properties were characterized. X-ray rocking curve of the (111) plane showed a full width at half maximum of 0.08°, indicating high crystalline perfection. Thermal analysis indicated significant volatilization of KTF at high temperatures. Spectral tests revealed an average transmittance of >90% in the 400-1600 nm range and an absorption coefficient of <0.007 cm^-1 at 1064 nm, demonstrating minimal optical loss suitable for high-power laser applications. Fluorescence lifetime was 4.82-4.99 ms for the Tb³⁺ ion at the ⁵D₄ energy level, which is 3-5 times longer than that in oxide matrices. This superiority is attributed to the suppression of non-radiative relaxation by the low-phonon fluoride matrix, enhancing the energy storage efficiency for laser emission. Based on above data, this study has successfully established a viable growth method for KTF crystals, providing a new technical pathway for the controllable synthesis of KTF and other ternary fluoride materials. All these results provide valuable insights for the high-efficiency application of KTF crystals in yellow-green laser emission.

Silicon carbide (SiC), as a representative wide bandgap semiconductor material, has increasingly demonstrated its significance in high-power, high-frequency and high-temperature electronic device applications. In recent years, SiC semiconductors have become primary material for power devices in electric drive modules and charging modules of new energy vehicles. Compared to Si-based insulated gate bipolar transistors (IGBTs), a kind of minority carrier device, SiC materials enable high-voltage resistance through majority carrier devices (such as Schottky barrier diodes and metal-oxide-semiconductor field-effect transistors (MOSFETs)) with high-frequency device structures, which conversely allows SiC to simultaneously achieve key characteristics of low on-resistance and high frequency. It is easy to deduce that, SiC will also play an indispensable role in emerging fields such as electric aircrafts, electric vertical take-off and landing (eVTOL) vehicles for low-altitude transportation, augmented reality (AR), photovoltaic inverters, and rail transportation. Among various SiC polytypes, 3C-SiC stands out due to its unique cubic crystal structure, higher thermal conductivity (500 W/(m·K)) and channel mobility (approximately 300 cm²/(V·s)), showcasing significant application potential and research value. This paper provides an overview of the crystal structure, fundamental physical properties, application advantages, and major growth methods of 3C-SiC, including chemical vapor deposition (CVD), continuous-feed physical vapor transport (CF-PVT), sublimation epitaxy (SE), and top-seeded solution growth (TSSG). Research progress and the latest achievements in 3C-SiC crystal growth using above techniques are reviewed, focusing on the thermodynamic characteristics and growth mechanisms of vapor-phase and liquid-phase methods. The microscopic processes of crystal growth are analyzed and summarized, and the future development directions and application prospects for 3C-SiC crystals are discussed.

In the post-Moore era, temporary bonding and ultra-thin wafer thinning of large-size functional wafers have emerged as essential technologies underpinning innovation within the semiconductor industry. However, challenges such as wafer warpage and breakage commonly encountered during wafer thinning severely limit device performance and yield. To address these issues, WAN’s group at Yongjiang Laboratory developed a cost-effective, room-temperature ultra-flat temporary bonding technique. This innovative process has significantly reduced the risk of wafer warpage while achieving high flatness and stability in wafer bonding. By integrating this process with domestically developed thinning equipment, the group successfully thinned 8-inch silicon wafers down to 8 µm, 12-inch silicon power chips to 15 µm with a total thickness variation (TTV) ≤2 µm, and 8-inch lithium niobate wafers to 8-10 µm, thereby satisfying diverse piezoelectric micro-electro-mechanical system (MEMS) application demands. Currently, this technology is widely applied in heterogeneous integration of various wafer materials, including silicon, lithium niobate/lithium tantalate, gallium oxide, and indium phosphide, providing crucial support for the localization and development of power chips and high-performance MEMS devices.

Diamond with excellent properties and broad application prospects in the fields of thermal management of optics and electronic devices, and wide bandgap semiconductors, is known as the ultimate semiconductor. As an optical window, a large-sized CVD (chemical vapor deposition) diamond free-standing thick film with a thickness of ≥2 mm is required. In semiconductor heat dissipation, a diamond free-standing film with a diameter over 4 inches (1 inch=2.54 cm) and a thickness of 100 μm is required to bond with semiconductor materials such as gallium nitride (GaN). However, there still exist significant difficulties in synthesis and application of large-area CVD diamond films. On the one hand, stress during the deposition process can cause the diamond film to rupture. On the other hand, residual stress can cause the diamond film to warp, resulting in poor bonding quality. Therefore, controlling the stress of diamond films has become a key issue for the large-scale and widespread application of diamond films. This article summarizes the classification, sources, and influencing factors of CVD diamond stress, and provides a detailed introduction to measures for suppressing stress in diamond films. Furthermore, researches on improving diamond properties by artificially applying stress are summarized, including changing diamond bandgap and increasing diamond thermal conductivity under stress. Finally, a method and theoretical calculation formula for evaluating the stress magnitude of diamond are provided, and the future trend of stress research on diamond films is analyzed.

Lithium niobate (LN) single crystals have emerged as one of the most valuable materials for integrated photonics materials due to their exceptional properties, including non-linear and electro-optical effects. Compared to congruent lithium niobate (CLN) crystals, near-stoichiometric lithium niobate (nSLN) crystals exhibit more pronounced non-linear and electro-optical properties, offering higher application value. nSLN crystals with high compositional uniformity can be prepared using a vapor transport equilibration method. However, large-size LN single crystals are highly susceptible to twinning defects and wafer cracks during diffusion processing. Here, large size nSLN single crystals were prepared using the vapor transport equilibration method to address the aforementioned defects and cracking. The twinning defects within wafers after diffusion processing were characterized, the mechanisms of twinning formation were analyzed, the wafer placement method to produce complete 4-inch (100 nm) and 6-inch (153 nm) wafers was modified, and the composition and transmittance of wafers were tested. Results indicate that composition of the wafers is at least 49.94% (in mole), approaching stoichiometric ratio, and their transmittance is greater than 71% across the 600-3300 nm range. Both Z-cut and X-cut wafers prepared by vapor transport equilibration method exhibited twinning defects. However, cracks were observed when twinning defects intersected on Z-cut wafers, whereas no cracks were present on X-cut wafers. The twinning planes on both Z-cut and X-cut wafers were depending on \left\{01\overline{1}2\right\}, which they were identified as deformation twins. According to the mechanism of deformation twin formation, the non-uniform deformation of lithium-rich materials is identified as the primary driving force beneath the twin formation. Ultimately, it was proposed to mitigate twin activation by modifying the diffusion treatment process, thereby increasing the yields of 4-inch (100 nm) and 6-inch (153 nm) nSLN wafers.

Lithium niobate crystal, combining its piezoelectric, nonlinear, electro-optical, and photorefractive properties, along with its stable physicochemical characteristics, has great potential for applications in integrated optics. However, designing thermal field for large-size lithium niobate crystal growth presents considerable challenges, considering the crucible shape being an important factor that significantly influences the crystal growth in which the diameter and height are compulsively restricted to the factors such as load capacity and crystal diameters. In this study, 4-inch congruent lithium niobate crystals were grown by using crucibles with two types of bottom shapes. The impacts of crucible bottom shape on the axial temperature gradient within the crystal and the melt near the crystal-melt interface, and the temperature distribution within the melt below the crystal-melt interface, were analyzed by numerical simulation. The impact of the crucible bottom shape on crystal growth was analyzed in contrast to crystal growth results. It is found that changes in the crucible bottom shape lead to variations in the temperature difference along the crucible sidewall and the temperature gradient within the melt, thereby altering the strength of natural convection in the melt. Compared to crucible with slipped bottom corner, the axial temperature gradient near the crystal-melt interface within the crystal and melt is large when using the crucible with curved bottom corner, and the axial temperature gradient within the melt below the crystal-melt interface is also large, and the natural convection is strong. Therefore, this study helps to solve the problems such as the unwanted crystal growth ridge spreading and the overgrowth of cellular interface.

Indium selenide (InSe) is a III-VI group semiconductor with interesting physical properties and has wide potential applications in the fields of photovoltaics, optics, thermoelectrics, and so on. However, the production of large-size InSe crystal is difficult due to the inconsistent melting of In and Se elements and peritectic reactions between InSe, In₆Se₇ and In₄Se₃ phases. In this work, a zone melting method, which has advantages of low cost and solid-liquid interface optimization, is employed for InSe crystal preparation. Because the initial mole ratio of In to Se is of great importance to InSe crystal growth, the non-stoichiometric In_0.52Se_0.48 solution was precisely used for growth based on the peritectic reaction of In-Se system, resulting in a InSe crystal productivity ratio at about 83%. An ingot with dimensions ϕ27 mm×130 mm is obtained with a typical slab-like InSe crystal in the size of ϕ27 mm×50 mm. The successfully peeled cleavage plane exhibits the good single-crystalline character as only (00l) peaks are detected in the X-ray diffraction pattern. This crystal has a hexagonal structure, and its elements are distributed uniformly in the matrix with transmittance of ~55.1% at 1800 nm wavelength, band gap energy of about 1.22 eV, a maximum electrical conductivity (σ) of about 1.55×10² S·m^-1 along the (001) direction, and a lowest thermal conductivity (κ) of about 0.48 W·m^-1·K^-1 perpendicular to the (001) direction at 800 K. These results imply that the zone melting method is indeed an effective approach for fabricating large-size InSe crystal, which could be applied for various fields. Above measured electrical and thermal behaviors are expected to provide a significant reference for InSe crystal application in the future.

The diamond film material holds great potential as a heat sink for GaN electronic devices. The diamond film layer with low stress, large dimensions, high quality, and an atomically smooth surface is crucial for enhancing the overall heat transfer capacity of GaN devices. This study presents a technique for growing and polishing polycrystalline diamond films on 3-inch(1 inch=2.54 cm) silicon substrates to facilitate the use of large-sized diamond film materials in radiator applications. Firstly, the study carries out multi-physical field self-consistent modelling of plasma in a microwave resonator. It then analyses the feasibility of depositing large diamond films using a microwave plasma chemical vapour deposition (MPCVD) device with a 2.45 GHz multi-mode ellipsoid resonator through simulation technology. The growth process parameters are optimized accordingly. After that, the diamond film is polished to meet the bonding requirements of GaN devices. The simulation results show that under the same microwave power input, the increase of chamber pressure leads to the increase of number density of plasma core electrons and H atoms, but the uniformity of radial distribution becomes worse. Diamond film is deposited under optimized conditions and mensurates that the thickness inhomogeneity of diamond film is 17%. In this process, methane at high concentration leads to pyramidal morphology of diamond grains dominated by (111) planes, accompanied by formation of twins. Full width at half maximum (FWHM) of the first-order characteristic peak of diamond in Raman spectrum is 7.4 cm⁻¹. After polishing, the surface roughness reaches 0.27 nm, the average bending degree of diamond film on silicon substrate is 13.84 μm, and the average internal stress is −40.7 MPa. Silicon substrate diamond wafers with large size, high crystal quality, low internal stress and atomically smooth surface are successfully prepared by the above method.

Calcium fluoride (CaF₂) crystals have good optical properties and chemical stability, and are often used as substrate materials in extreme edge optical window scenes. It is noteworthy that as one of the key properties of UV laser window materials, the radiation damage resistance of CaF₂ crystal increases too fast due to the cleavage effect, and the actual damage threshold is much lower than the theoretical value, which cannot meet the needs of UV high-power laser devices, and is the main factor limiting its application in high-power UV lasers. In this study, material composition design was used to introduce F_i^- by doping inert rare earth Y³⁺, and the cluster effect between Y³⁺ and F_i^- was used to increase the bonding number between the cleavage planes, so as to enhance the interlayer bonding force, reduce the cleavage effect and raise the damage threshold. CaF₂ crystals doped with Y³⁺ were prepared under the same condition by using a porous crucible, and their optical quality, mechanical properties and thermal properties of the doped CaF₂ crystals were characterized and analyzed. The experimental results show that appropriate amount of Y³⁺ doping has little effect on the optical and thermal properties of CaF₂ crystals, such as transmittance, thermal expansion coefficient and thermal conductivity, and does not affect the performance of CaF₂ crystals. However, the influence on mechanical properties, such as shear strength, is relatively prominent. When the optimized doping concentration is 0.36% (in atom), the shear strength is increased by 68.4%, and the corresponding laser induced damage threshold of Y:CaF₂ crystal is increased by 166%.

As the third generation semiconductor material, gallium nitride (GaN) is widely used in electronic devices and optoelectronic devices due to its excellent characteristics such as wide band gap, high breakdown field strength, high electron mobility, outstanding thermal conductivity, and direct band gap. However, it is difficult to obtain high quality single crystal GaN thin films due to the mismatch between GaN material and substrate in early phase of preparation. Until the two-step growth method is proposed, in which the nucleation layer of aluminum nitride (AlN) is firstly grown on the substrate at low temperature, and then GaN is grown at high temperature, the quality of GaN is greatly improved. Nowadays, AlN nucleation layers are fabricated via magnetron sputtering and molecular beam epitaxy, etc. To further improve the quality of GaN crystals, this study used plasma-enhanced atomic layer deposition (PEALD) method to prepare AlN nucleation layers for the epitaxial growth of GaN on a two-inch c-plane sapphire substrate. Compared with the magnetron sputtering method and molecular beam epitaxy method, the crystal quality of AlN prepared by PEALD method displays advantages of simple process, low cost and high yield. Measurements on deposited AlN films show that the deposition rate is 0.1 nm/cycle and the films have island-like structures varying with its thickness. Epitaxial GaN measurements show that GaN epitaxial layer can obtain the smoothest surface with a root mean square roughness of 0.272 nm, the best optical properties, and the lowest dislocation density when AlN is deposited with a thickness of 20.8 nm. In conclusion, a new method of epitaxial single crystal GaN on AlN prepared by PEALD has been built with optimal deposition at 20.8 nm of AlN to obtain high quality GaN thin films, it can be used to prepare high electron mobility transistors and light-emitting diodes.

Heteroepitaxy provides an effective path for the synthesis of diamond wafers. After more than 20 years of development, the diamond nucleation and growth technology on iridium substrates has enabled to prepare crystals with a maximum diameter of 3.5 inches, which opens a door to application diamond as ultimate semiconductor in the future chip industry. However, a series of problems that occur on heterogeneous substrates, such as surface nucleation, bias process window, and diamond epitaxial growth, need to overcome from the perspective of growth thermodynamics. In this study, aiming at the key issue how diamond can achieve epitaxial nucleation and growth in chemical vapor deposition atmosphere, a simulation study was carried out on the nucleation and growth process of diamond at the atomic scale based on the first-principle calculation. The results show that the adsorption of C atoms on the surface of the Ir substrate is more stable than that on the bulk phase, which indicates that diamond nucleation can only occur on the substrate surface. The number of C atoms of sp³ hybridization in the amorphous hydrogenated carbon layer increases firstly and then decreases with the increase of ion kinetic energy under ion bombardment, confirming the existence of the ion kinetic energy or bias voltage window in the high-density nucleation of diamond. The interfacial binding energy is the lowest (about -0.58 eV/C) when diamond is epitaxially grown along the Ir substrate, meaning that the interface binding energy is the decisive thermodynamic factor for the epitaxial growth. In conclusion, this study clarifies the thermodynamic mechanism of single crystal diamond epitaxial growth under the bias-assisted ion bombardment, and points out a great significant guidance for the growth of diamond and other carbon based semiconductors.