Barium fluoride (BaF2) crystal is known as the fastest scintillation crystal, which has a wide application prospect in high energy physics, nuclear physics and nuclear medicine. It is very important to suppress the slow luminescence component of BaF2 crystal for its engineering application. BaF2 crystals with high Y3+ doping concentration 5%, 8%, 10% (mole fraction) were prepared by Bridgman method, and the codoped BaF2 fast response scintillation crystals were prepared by codoping Y3+ with alkali metal ions (Li+, Na+) to form charge compensation to eliminate the generation of interstitial F-. Then, based on the optimized 5 ns and 2 500 ns time gate width measurement methods, the effects of Y3+ doping concentration and the codoping concentration of Y3+ and alkali metal ions (Li+, Na+) on the fast/slow component ratio of BaF2 scintillation crystal were studied. The results show that the optical quality of the high concentration Y3+ doped BaF2 crystals is excellent, and the transmittance at 220 nm and 300 nm is higher than 90% and 92%, respectively. With the increase of Y3+ doping concentration from 0 to 10%， the slow luminescence component of BaF2 crystal decrease significantly, and the fast/slow component ratio increase from 0.15 to 1.21. The slow luminescence component of the grown Y3+/Li+ and Y3+/Na+ codoped BaF2 crystals are further decrease compared with that of the Y3+ doped BaF2 crystals, and the highest fast/slow component ratios obtained are 1.63 and 1.61, respectively. The codoped BaF2 fast response scintillation crystal is expected to be applied in the frontier experiments of high energy physics and nuclear physics.

Ce∶LuAG crystal is an excellent scintillation material, but cracking and inclusion defects often occur when Ce∶LuAG is grown by Czochralski method. In this paper, the effects of temperature gradient, pulling speed, rotation speed and thermal strain on crystal defects were analyzed by combining theory with practice, and the solution was put forward. The suitable technological parameters for growing Ce∶LuAG crystal with high quality are given: the temperature gradient above the melt is about 5 ℃/mm, the shoulder angle is 30°~60°, the pulling speed is 1.0~1.5 mm/h, and the crystal rotation speed is 15~25 r/min. Finally, good quality of Ce∶LuAG single crystal with a diameter of 30 mm and an equal diameter length of 50 mm is successfully grown, and the crystal core area is small.

Due to the influence of crystal size and nonlinear optical properties, the available nonlinear crystals are very limited. As a traditional largesize photoelectric material, DKDP crystal has been applied in optical parametric chirped pulse amplification (OPCPA) devices. Highly deuterium DKDP crystals have better optical properties, but the growth of highly deuterium DKDP crystals has more stringent requirements on the growth environment. In this paper, highly deuterium DKDP crystals were successfully grown by rapid growth of point seed crystals through an improved raw material synthesis tank and the growth tank. The samples were prepared according to the type I (θ=37.23°, φ=45°) cutting method, and their deuterium content, transmittance, optical homogeneity and laserinduced damage threshold of crystals were tested. The results show that the average deuterium content of the crystal reaches 98.49%, and the crystal has a wide transmission band and high transmission performance in the visiblenear infrared band. The test results of Ron1 show that the laserinduced damage threshold of DKDP crystal reaches 19.92 J/cm2 at 3 ns, 527 nm. The rootmeansquare of optical homogeneity of the crystal reaches 1.833×10-9, indicating that the crystal has good optical homogeneity.

Indium antimonide (InSb) materials have been widely used in infrared photoelectric detectors and other fields because of their special properties. With the development of larger arrays of midinfrared focal plane detectors and a growing demand for lowcost InSb infrared detectors, the desired size for the InSb wafers also increases. In this paper, a new structure of graphite rest and high precision low damage single line cutting were combined to develop a 5 inch InSb crystal oriented segmentation. Low damage edge chamfering techniques while optimizing grinding parameters were used to improve the grinding of 5 inch InSb wafers. An optimized mounting process were used to further improve the flatness of polished 5 inch InSb wafers. Furthermore, the pH value and polishing solution ratio were optimized to improve the surface quality of 5 inch InSb wafers. At the same time, the crystal orientation and deviation, polished surface macroscopic quality, geometric parameters, surface roughness and lattice quality of 5 inch InSb wafers were analyzed using an Xray crystal orientation instrument and atomic force microscope. The test results show that, high quality 5 inch InSb wafers can be created more readily by this newly optimized process, helping to meet the current demand for InSb materials in IR detectors and other fields.

In this paper, a new phononic crystal structure with periodic units consisting of four tungsten vibrators wrapped by silicone rubber coating is designed. The dispersion curve, vibration mode and transmission loss spectrum of the structure were calculated by finiteelement method(FEM). The results show that the bandgap range of this structure is 18.85~225.28 Hz, which is consistent with the frequency attenuation range of transmission loss spectrum, and can effectively suppress the propagation of elastic waves of 20~200 Hz in phononic crystals. By analyzing the vibration mode corresponding to the point on the dispersion curve, the formation mechanism of the bandgap is explained. The influence of the notch angle of the phononic crystal plate and the longitudinal and transverse spacing between the phonons on the bandgap was discussed in this paper. The results show that as the notch angle decreases, the lower boundary of the bandgap remains almost unchanged, and the upper boundary of the bandgap rises, thus increasing the width of the bandgap.As the transverse or longitudinal spacing between the vibrators increases, the lower and upper boundaries of the bandgap rise, and the width of the bandgap increases, thus the bandgap of the phononic crystal model is optimized. At the same time, the notch design of the phononic crystal plate save the material and reduce the weight of the structure.

In the process of preparing silicon single crystal, the Czochralski method has problems such as multiple mechanism assumptions, unclear boundary conditions under multiple field couplings, interlaced and mutual influence of physical and chemical changes, which makes it impossible to establish an accurate mechanism model for silicon single crystal growth process control. To solve this problem, based on a large amount of crystal growth data in the single crystal furnace pulling workshop, this paper analyzes the characteristic parameters related to crystal diameter based on the maximum information coefficient （MIC） algorithm proposed by the mutual information theory. Then, based on the nonlinear autoregressive with exogeneous inputs (NARX) dynamic neural network, a multiinput, and singleoutput equaldiameter phase crystal diameter prediction model was established, the diameter prediction was also performed for the three single crystal furnace pulling data, and the average mean square error value of the prediction is 0.000 774. Finally, the prediction model of crystal diameter in the equal diameter stage established based on the NARX dynamic neural network is compared with the prediction model of crystal diameter in the equal diameter stage established based on the back propagation (BP) neural network. The results of the comparative analysis verified the superiority of the NARX dynamic neural network model for predicting the crystal diameter in the isodiametric stage. The results show the NARX dynamic neural network provides a more accurate identification model for the control of crystal diameter.

In this paper, the effect of the process parameters of reciprocating diamond wire saw on the surface quality of the (001) plane βGa2O3 single crystal was investigated. According to the theory of the indentation fracture mechanics, the abrasive behavior and material removal mechanism in the process of cutting βGa2O3 single crystal with diamond wire saw were investigated. The influence of the cutting direction on the surface quality of the (001) plane βGa2O3 single crystal was analyzed from the aspect of anisotropy, SEM and SJ210 roughness measuring instrument were used to explore the effect of process parameters on the quality of wafer surface after diamond wire saw. The experimental results show that the depth of subsurface damage layer can be reduced and the surface quality of the wafer can be effectively improved by increasing the wire speed or decreasing the feed rate.

MoTe2 has been widely studied due to its special stacking mode and rich phase structure, especially the suitable band gap which makes it have a promising application in the field of optoelectronic devices. Based on the nonequilibrium Green’s functiondensity functional theory, the influence of different atomic vacancy defects on the photogalvanic effect of monolayer 2HMoTe2 was studied by the firstprinciples calculation method. The results show that the photocurrent function of 2HMoTe2 devices with different vacancies is consistent with the phenomenological theory. In the photon energy range from 1.0 eV to 2.8 eV, 2Te vacancy significantly improves the photocurrent of 2HMoTe2, especially when the photon energy is 2.6 eV, the maximum photocurrent of all devices is obtained. With the energy band structure, it is found that different atomic vacancy defects lead to the shift of the valence band to the high energy level and the conduction band to the low energy level, which reduces the band gap between the four devices and conducive to the transition of electrons from the valence band to the conduction band to form photocurrent under the irradiation of linearly polarized light. It is found that the monolayer 2HMoTe2 of 1Te vacancy and Mo vacancy has a similar energy band structure far away from the Fermi level, which leads to the same change trend of the device photocurrent when the photon energy is greater than 1.6 eV. These results can be used to guide the design of MoTe2 optoelectronic devices.

Based on the plane wave ultra soft pseudopotential method of density functional theory, the geometric structure, energy band structure, electronic density of states and optical properties of wurtzite CdS containing Cd vacancy defect and wurtzite CdS containing S vacancy defect were studied by the firstprinciple. According to calculation and analysis, the CdS systems containing Cd vacancy defects are all ptype semiconductors and the transition modes of CdS systems containing S vacancy defects are all changed from direct transition to indirect transition. The density of states and total energy of CdS system with Cd and S vacancy defects decrease. The static dielectric constant of vacancy CdS system is higher than that of intrinsic CdS system, and increases with the increase of vacancy concentration. The vacancy defect system of Cd is more obvious, and the polarization ability is significantly improved. The CdS system of Cd vacancy has obvious absorption in infrared band compared with the intrinsic CdS system, and the CdS system of S vacancy has obvious absorption in visible light compared with the intrinsic CdS system.

The effect of strain on the electronic structure and optical properties of Mo2C(001) surface were studied by the firstprinciples method. The band structure results show that Mo2C(001) surface is an indirect band gap semiconductor, and the band gap decreases with compressive strain and tensile strain increasing. When the strain is -20%, Mo2C surface (001) changes from an indirect band gap semiconductor to metal. When the strain is -20%, -15%, -10%, -5%, 0%, 5%, 10%, 15% and 20%, the band gap is 0 eV, 0.162 eV, 0.376 eV, 0.574 eV, 0.696 eV, 0.708 eV, 0.604 eV, 0.437 eV and 0.309 eV, respectively. The reason for the change of band gap is mainly that, the electrons of Mo 4p, 4d, 5s and C 3p states become sensitive to each other are excited under difference strains, and the activity is enhanced. The results valence band top is changed among the points of G, A, L and M, and the conduction band bottom is changed between the points K and H in Brillouin region. When the strain gradually changes from -15% to 20%, the first peak of the absorption spectrum gradually decreases, the photoelectron energy corresponding to the first peak decreases, and the absorption band edge moves to the low energy direction, indicating that the optical absorption increases with the increase of compressive strain, and the absorption band edge moves to the low energy direction with the increase of tensile strain. At the same time, other optical properties show similar changes with the strain change. The calculation results of optical properties show that the strain effectively adjust the optical absorption characteristics. The research results provide theoretical support for the application of Mo2C (001) as new optoelectronic material.

In order to further understand the relationship between the structure and luminescence properties of ZnMgO alloy thin films, the targets for films were prepared by ball milling ZnO and MgO powders, cold pressing, and high temperature sintering. ZnMgO thin films of Mg content ranging from 0% to 8% (atomic number fraction) were prepared by RF magnetron sputtering on quartz substrates at room temperature and annealed at 400 ℃ in air atmosphere afterwards. The crystal structure of the film was characterized by Xray diffractometer, the morphology and chemical composition of the particles were observed by field emission scanning electron microscope and the Xray energy dispersive spectrometer (EDS), the photoluminescence (PL) spectra were measured by fluorescence spectrophotometer. ZnMgO thin film is found to be a solid solution with wurtzite hcp structure. With the increase of Mg content, the morphology changes from approximately round to round and random polygon mixture, which is attributed to the grain thickness of (002) losing its dominance and its growth rate exceeded by (101) and (110). The PL spectrum shows a strong violet peak (390～393 nm) and a weak near infrared (NIR) peak (758～765 nm). With the increase of Mg content, the location of violet peak first blueshifts and then redshifts, while the NIR peak redshifts. All peak positions redshift and the intensity increase significantly after annealing at 400 ℃. The generation and variation mechanism for the violet and NIR peaks before and after annealing are discussed.

The electronic properties and interface contact of graphene/WSSe van der Waals heterojunction by means of tuning the interlayer distance and external electric field were studied by the firstprinciples calculation method. The electronic properties of constituent monolayers can be retained in graphene/WSSe heterojunction because of the van der Waals force. A small band gap value (7 meV) can be found in the Dirac cone of graphene in graphene/WSSe heterojunction. The builtin electric field generated by the charge transfer plays a key role in the effective hindrance of photoexcited carrier recombination. The graphene/WSSe heterojunction possesses enhanced optical absorption in the visible light range compared with two freestanding monolayers, implying its potential application in optoelectronic device. Besides, the graphene/WSSe heterojunction displays the ntype Schottky contact characteristics at the equilibrium interlayer distance. Both the interlayer distance and external electric field can be used to modify the Schottky barrier height and contact types of graphene/WSSe heterojunction, and effectively adjust the Dirac cone position of graphene. The research in this paper provides a theoretical basis for the fascinating applications of graphene/WSSe heterojunction in the fields of nanoelectronic and optoelectronic devices.

The stacked passivation films for emitter of TOPCon solar cells were investigated in the paper. The passivation performance of three different stacked films (SiO2/SiNx, Al2O3(1.5 nm)/SiNx, SiO2/Al2O3(1.5 nm)/SiNx) were compared. The results show that the Al2O3 (1.5 nm)/SiNx films exhibit better passivation performance than that of the SiO2/SiNx films, and the SiO2/Al2O3(1.5 nm)/SiNx films perform the best, with an implied open circuit voltage of 705 mV. Based on the Al2O3/SiNx stacked passivation films, the effect of Al2O3 thickness (1.5 nm, 3 nm and 5 nm) on the passivation performance and photoelectric conversion efficiency of cells were investigated. When the thickness of Al2O3 increases from 1.5 nm to 3 nm, the passivation performance is significantly improved, the mean value of the implied open circuit voltage increases by 20 mV to 707 mV, and the conversion efficiency of the corresponding cells increases by 0.23 percentage point, which is comparable to that of the SiO2/Al2O3(1.5 nm)/SiNx stacked films cells. However, when the thickness of Al2O3 continues to increase to 5 nm, the mean value of the implied open circuit voltage remains unchanged. Therefore, Al2O3(3 nm)/SiNx stacked films can be used to replace the SiO2/Al2O3(1.5 nm)/SiNx stacked films, which not only simplifies the process flow of the solar cells, but also reduces the production cost.

Hexagonal Y1-xHoxMn0.8Fe0.2O3 polycrystalline samples were synthesized by hightemperature solidstate reaction method. The effects of Ho3+ doping on microstructure and magnetic properties of YMn0.8Fe0.2O3 were investigated in this paper. Xray diffraction (XRD) and Raman spectra (RS) show that all samples are of singlephase hexagonal structure without another impurity phase. When the doping concentration (x) of Ho3+ is lower than 0.15, the lattice constants, unit cell volume and bond length between the Mn—O of the samples decrease with x increasing. The decrease of the lattice constants may be related to the interaction between the Mn3+/Fe3+ 3d orbital and the Ho3+ 4f orbital, resulting in lattice distortion and electron loss. The displacements of the rareearth atoms at the Asite relative to the plane and the inclination of the MnO5 bipyramids are suppressed with increasing doping concentration, which is demonstrated by the shift deviations of the rareearth atoms and the variations of the Raman phonon modes. At the same time, the trimerization of Mn3+ at the Bsite is weakened. The magnetic properties of the samples were measured using the superconductor quantum interference device (SQUID). Results show that the antiferromagnetic (AFM) order decreases upon Ho3+ doping, consistent with the reduced superexchange interaction between Mn3+—O2-—Mn3+. The AFM transition temperature TN decreases. Besides, the magnetization of the samples and the weak ferromagnetic (WFM) order at low temperature are significantly enhanced, which is attributed to the suppressed magnetic resistance behavior of the system and the ferromagnetic order generated by the spin exchange interaction between Ho3+—O2-—Mn3+. These provide an idea for us to further explore room temperature multiferroic materials.

CsPbBr3Cs4PbBr6 perovskite composite nanocrystals (NCs) were successfully prepared by mechanochemistry method at room temperature, introducing trace amounts of methanol and oleylamine as ligands. The nanocrystals were tested by powder Xray diffraction (XRD), elemental content analysis (EDS), ultravioletvisible spectroscopy (UVVis), photoluminescence(PL) spectroscopy and transmission electron microscopy (TEM). Compared with the samples without methanol, the luminescence intensity of the samples with 0.85 mL methanol increases by 58%, and the quantum yield (PLQY) increases from 11% to 55%. Moreover, the presence of Cs4PbBr6 in the composite NCs improves the stability of the samples at room temperature. This experiment confirm that the introduction of methanol in the mechanochemistry preparation process could adjust the composition of the complex nanocrystals, thus significantly improving the luminescence intensity and stability of the products, which provides a new idea for the synthesis of luminescent nanocrystals at room temperature.

In this paper, a series of purephase Bi2Fe4O9 nanocrystals were synthesized by adding different content of FeCl2 in the process of hydrothermal method, and the lower valence iron ions were successfully introduced into Bi2Fe4O9. The UVvisible absorption spectrum data proves that the addition of FeCl2 reduces the optical band gap of Bi2Fe4O9 from 2.06 eV to 1.96 eV. Both the scanning electron microscope images and Xray diffraction patterns prove that the synthesized samples are purephase square flakes Bi2Fe4O9 nanocrystals. Three synthesized Bi2Fe4O9 nanocrystal samples (S1, S2, S3, the FeCl2 content of the three samples increased from 0 during the synthesis process, corresponding to x=0, 0.2 mmol, 0.4 mmol, respectively) were used for photocatalytic degradation of methyl orange solutions under a 500 W mercury lamp irradiation. It is found that the photocatalytic degradation rate of the three samples is the fastest when 20 μL of hydrogen peroxide is added, and the photocatalytic degradation rate of the S3 sample is faster than that of S1 and S2. In the case of appropriate addition of hydrogen peroxide, the addition of FeCl2 can improve the performance of Bi2Fe4O9 in photocatalytic degradation of dye molecules.

The xLi0.5Bi0.5MoO4(1-x)Li2Zn2(MoO4)3 ［xLBM(1-x)LZM］ composite ceramics were prepared by traditional solidstate reaction method. The sintering characteristics, phase composition, microstructures and microwave dielectric properties of LZM ceramics with different mass fraction (x=25%, 30%, 35%, 40% and 45%) of LBM were investigated. The results show that, LBM effectively adjust the resonant frequency temperature coefficient (τf) of LZM ceramics to near zero and also decreases the sintering temperature; LBM can coexist with LZM, and no new phases are detected in addition to the LZMT and LBM phase. With the increase of LBM ceramics, the sintering densification temperature decreases gradually, the bulk density of composite ceramics initially increases and then decreases, the permittivity (εr) and τf increases, the quality factor (Q×f) decreases gradually. When 40%LBM ceramics is added, LZMLBM composite ceramics sintered at 600 ℃ for 2 h obtained maximun bulk density of 4.41 g/cm3，and excellent microwave dielectric properties of the εr is 13.8, the Q×f is 28 581 GHz and τf is -5×10-6/℃．

In this paper, magnesium aluminate spinel (MgAl2O4) materials were prepared by traditional solidphase sintering method with high purity fused magnesia and calcined active aluminum powder as raw materials, and NiO as additive. The MgO and Al2O3 powders were mixed in a theoretical molar ratio of 1∶1, and NiO with mass fraction of 0%, 0.5%, 1.0%, 1.5%, and 2.0% NiO were introduced into the system, respectively. The effects of NiO addition on sintering properties, phase composition and microstructure of MgAl2O4 were studied by Xray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). The results show that the introduction of appropriate amount of NiO can significantly promote the formation of MgAl2O4 phase and grain growth. At 1 600 ℃, when the NiO content is lower than 1.5%, NiO can completely dissolve into MgAl2O4 crystal lattice and preferentially replace Al3+, which improves the defect concentration in MgAl2O4 crystal and activates the lattice, thus promoting the sintering of MgAl2O4. When the NiO content is higher than 1.5%, more second phase NiO appears in the MgAl2O4, which hinders the mass migration and transmission, and it is not conducive to the improvement of sintering performance of MgAl2O4.

A SiC single crystal boule with a diameter of 209 mm was grown by physical vapor transport (PVT) method with a diameter expansion technique. Standard 8inch SiC single crystal substrates were fabricated by using the processes of multiwire sawing, grinding, polishing and cleaning. Crystal polytype, crystal quality, micropipes, resistivity, stress, wafer shape, dislocation of a randomly selected 8inch substrate were characterized by Raman spectrometer, highresolution Xray diffractometer, optical microscope, resistivity tester, polarization stress meter, wafer flatness tester, and dislocation detector. Raman spectra show that 8inch substrate consists only 4H polytype. Xray rocking curves illustrate fullwidth at halfmaximum of the (004) peak between 10.44″ and 11.52″. Micropipe density is 0.04 cm-2 and the average resistivity is 0.020 3 Ω·cm. There is no stress concentration zone in the substrate with an evenly distributed stress. Warp and bow are 17.318 μm and -3.773 μm, respectively. The average dislocation density is 3 293 cm-2 by scanning the full area of the molten KOH etched 8inch substrate, among which the density of threading screw dislocation(TSD), threading edge dislocation(TED) and basal plane dislocation(BPD) are 81 cm-2, 3 074 cm-2 and 138 cm-2, respectively. All results indicate the high quality of the 8inch n type 4HSiC substrate, which reaches worldclass levels according to the comparsion with the industry standards.

Silicon carbide (SiC), as a typical representative of the thirdgeneration semiconductor material, has performance advantages in wide band gap, high thermal conductivity, high breakdown electric field and large electron drift velocity, etc., and is considered to be one of the ideal materials for high temperature, high frequency, high power and high voltage devices. SiC can effectively break through the physical limits of traditional Sibased power semiconductor devices, known as a green energy device that drives the “new energy revolution”. As the core material for the manufacture of power devices, the growth of SiC single crystal substrate is very important, especially the preparation of single 4HSiC polytype. Due to the better crystallographic compatibility and similar formation free energy among different polytypes, the grown SiC bulk crystals are prone to produce polytype inclusions and then seriously affect the device performance. Therefore, in this paper, the basic principle, growth process and existing problems of SiC crystal prepared by physical vapor transport (PVT) method are summarized firstly. Then the possible inducing factors for the formation of polytype inclusions were given and the relevant mechanisms are also discussed. In addition, the common identification methods of SiC polytype structures are further introduced. Finally, a prospect for the research of SiC single crystal are made.

As a new generation of display technology, microLED demonstrates the advantages of high brightness, low energy consumption, long life, and selfluminous. However, the technical bottlenecks, such as difficulties in achieving highefficiency fullcolor displays, have hindered their industrialization processes and popularity. The fullcolor display is a crucial technology for the commercialization of microLED. However, with the high degree of integration and miniaturization of LED chips, the mass transfer of RGB chips to the same substrate for achieving fullcolor display has resulted in high costs and low yields. Therefore, there is an urgent need to discover a simpler and more efficient method for fullcolor display. This paper provides an overview of microLED microdisplay device fabrication technologies and several methods for achieving fullcolor displays, focusing on the quantum dots color conversion layer method, the RGB direct alignment method, the special structure method, and the optical lens method. The technical challenges and development trends of microLED microdisplays are also discussed.

MAX phases are a group of layered ternary carbides and/or nitrides. M is an early transition metal, A is mainly an element in ⅢA, ⅣA and ⅤA groups, and X is C and/or N. These compounds have characteristics of both ceramics and metals, such as excellent conductivity, thermal conductivity, corrosion resistance and antioxidant properties. And they have potential applications in many fields. In recent years, many MAX phases with new elements, new structures and solid solutions appear and then enrich the family of MAX phases. The MAX phase solid solutions are obtained by adding elements into the crystal structures of MAX phases. 127 MAX phase solid solutions which can be divided into four types are summarized in this paper. The structural change and performance regulation of MAX phase solid solutions are analyzed, and the existed theoretical problems and the key technologies that need to be solved urgently are pointed out. Finally, the research directions and developing trends of MAX phase solid solutions are prospected.