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.

Dy³⁺-doped SrGdGa₃O₇ crystal was successfully grown through the Czochralski method and investigated in detail for its structural and optical features. Its crystallographic lattice parameters were optimized by Rietveld refinement based on XRD data. Polarized absorption spectra, polarized emission spectra, and fluorescence decay curves of Dy: SrGdGa₃O₇ crystal were analyzed. Absorption cross-sections at 452 nm corresponding to π- and σ-polarization were computed as 0.594×10^-21 and 0.555×10^-21 cm², respectively. Calculated effective J-O intensity parameters Ω₂, Ω₄, and Ω₆ were 5.495×10^-20, 1.476×10^-20, and 1.110×10^-20 cm², respectively. J-O analysis and emission spectra show that transition ⁴F_9/2→⁶H_13/2 of Dy: SrGdGa₃O₇ crystal has the highest fluorescence branching ratio and fluorescence intensity under 452 nm excitation within the visible spectral region, the emission cross-sections of π- and σ-polarization were 1.84×10^-21 and 2.49×10^-21 cm² at the wavelength of 574 nm, respectively. The measured radiative lifetime and fluorescence decay time of the Dy³⁺: ⁴F_9/2 level were 0.768 and 0.531 ms with a quantum efficiency of 69.1%. All these results reveal that Dy³⁺: SrGdGa₃O₇ crystal is a promising material for yellow lasers pumped with blue laser diodes.

Microwave plasma chemical vapor deposition (MPCVD) technology is an ideal way to prepare large size and high-quality single crystal diamonds. However, the complexity of MPCVD single crystal diamond growth and the diversity of crystal growth requirements make it difficult to optimize the growth process. To address this issue, a systematic design method for MPCVD single crystal diamond growth based on plasma diagnostic technology was proposed, using plasma imaging and spectral analysis to quantitatively diagnose microwave plasma. The physical coupling characteristics and quantitative relationship between pressure, microwave(MW) power, plasma properties, and substrate temperature were studied by using home-made MPCVD system. And the size of major axis, precursor group concentration and distribution, energy density, and other data of the plasma under different parameters were obtained. Based on experimental data, the growth process map of single crystal diamond was obtained. According to this map, we selected process parameters by growth temperature and growth area. Through experimental verification, it is shown that this map is usful for guiding prediction with parameter error of less than 5%. Simultaneously, based on the predicted map, growth of single crystal diamond under different plasma energy densitiesis studied. At lower power (2600 W), a higher energy density (148.5 W/cm³) was obtained, and the concentration of carbon containing precursors was higher than that of the other parameters, resulting in a higher growth rate (8.9 μm/h). By this method system, effective plasma control and process optimization can be carried out meeting for different single crystal diamond growth.

Silicon carbide (SiC) has wide application in electric vehicles, rail transit, high voltage power transmission and transformation, photovoltaic, and 5G communication owing to its excellent physical and chemical properties. 8-inch SiC substrate has great potential in reducing unit cost of devices and increasing capacity supply, and has become an important technology development direction of the industry. Recently, Shandong University and Guangzhou Summit Crystal Semiconductor Co., Ltd. have made a major breakthrough in the control of dislocation defects in 8-inch SiC substrates. The 8-inch n-type 4H-SiC single crystal substrate with low dislocation density has been fabricated by physical vapor transport (PVT) method, of which the threading screw dislocation (TSD) density is 0.55 cm^-2, and the basal plane dislocation (BPD) density is 202 cm^-2.

The shoulder of the crystals grown by the Czochralski method is generally inclined, leading to poor quality and difficult processing, which then result in low utilization rate of the grown crystal. Take congruent lithium niobate (CLN) crystal as an example, this study used numerical simulation and experimental method to investigate the thermal field and growth process of flat shoulder crystal growth by the Czochralski method which can well acceptedly overcome the above problems. The result shows that the shape of the solid-liquid interface should be convex toward melt at the stage of shouldering. Temperature gradient near solid-liquid interface can be reduced by lowering the after-heater position (10 mm) to avoid the formation of polycrystalline. Control of the shouldering speed is the main way while control heating power is the accurate way to ensure the trend of shouldering. Accelerating the speed at the initial stage of shouldering (ϕ≤30 mm) and slowdown the speed at the middle and later stage of shouldering (ϕ≥35 mm) can shorten the period of shouldering and avoid defect inclusion. The pulling rate (0-1.5 mm/h) can be changed rapidly (1.5-2 h) without affecting the trend and quality of shouldering by adjusting power with a small amplitude (Δt=10 min, ∆v= 0.2 mm/h). By using these adjusting ways to thermal field and growth process, a series of 3-inch (1 inch=25.4 mm) flat shoulder CLN crystals with good optical homogeneity have been successfully grown.

Besides its application as nonlinear optical devices, La₂CaB₁₀O₁₉ (LCB) crystal has been extensively studied as a host crystal due to excellent properties. Nevertheless, rare-earth (RE) ions doped LCB crystals for ultraviolet (UV) lasers have not been studied yet. In this work, Ce³⁺ doped La₂CaB₁₀O₁₉ (Ce³⁺:LCB) crystal with the size of 40 mm×21 mm×6 mm was grown by top-seeded solution growth (TSSG) method. Its lattice parameters are slightly different from that of the LCB crystal, and its X-ray rocking curve indicates that the Ce³⁺:LCB is of high crystalline quality. Transmittance spectrum and UV absorption spectrum measured at room temperature show intense absorption in the ranges of 200-288 nm and 305-330 nm,and Sellmeier equations for the refractive indices were determined by least-squares method. The excitation and fluorescence spectra show that there are two broad excitation peaks at 280 nm and 316 nm, corresponding to transitions of Ce³⁺ ions from 4f to 5d. Four emission peaks were obtained at 290, 304, 331, and 355 nm, which correspond to transitions from 5d state to ²F_5/2 state and ²F_7/2 state. Ce³⁺:LCB crystal exhibits high thermal conductivity (6.45 W/(m·K)) at 300 K, and keeps good thermal stability with the increase of temperatures. Its thermal expansion coefficients and lattice parameters of c direction linearly enlarge from 2.94×10^-6 /K and 0.91240 nm to 5.3×10^-5 /K and 0.91246 nm in the temperature range from 358 K to 773 K, respectively. These results demonstrate that Ce³⁺:LCB crystal has excellent optical properties and good thermal stability, which is conducive to its application for UV lasers.

Radiation resistance of CaF₂ crystal is one of the critical properties in the application of deep ultraviolet lithography, but the damage process under 193 nm laser irradiation is still unclear. This paper reports the damage behavior of CaF₂ crystals under 193 nm laser irradiation and the key defect factors affecting the damage. Through the 193 nm laser irradiation experiment, it is found that the crystal damage is mainly manifested as the radiation-induced color centers inside the crystal and the radiation-induced damage pits on the surface. Irradiation-induced color centers were analyzed by UV-visible spectrophotometer, and linear fitting was performed between absorption coefficients of different color centers and Y impurity contents. The results show that Y ion has a low-order orbit that overlaps with the F center structure wave function, and hybridizes to form a stable structure. There is a linear relationship between Y ions contents and intrinsic color centers of CaF₂ crystals, confirming that Y element is the key impurity ion affecting the formation of color centers. Energy dispersive X-ray spectrometer (EDS) results show that the content of calcium in the damage pits increases and the content of fluorine decreases, which confirms that the diffusion of H centers and the aggregation of F centers lead to irradiation damage. Electron backscatter diffraction (EBSD) results show that surface irradiation damage occurs preferentially at dislocations. Therefore, reducing the impurity content and dislocation density is an important way to improve the anti-irradiation damage performance of calcium fluoride crystals under 193 nm laser.