Commercial coating design software based on optical transfer matrix theory and traditional method of correlation analysis arc used to obtain a series of simulated reflection spectrum of ultraviolet AlGaN-based Bragg reflector (center wavelength of 314 nm). The correlation between partial structural parameters and reflectivity or center wavelength arc studied, as well as the correlation coefficients. The results of correlation analysis show that the thickness of the AlGaN layer is the most impact factor on the reflectivity and the center wavelength, which is a negative correlation. Bases on this conclusion, we obtain an optimal UV AlGaN DBR structure with high reflectivity and wide detection band. Furthermore, the correlation analysis and optimization results match the actual data, which provide a new way and method for the design and application of UV AlGaN DBR.

A CdZnO/ZnO multiple quantum-well light-emitting diode (LED) structure was successfully grown by using plasma-assisted molecular beam epitaxy on a p-GaN template that had been grown by using metal-organic chemical-vapor deposition on a c-sapphire substrate. The properties of the sample were characterized by using high-resolution X-ray diffraction, transmission electron microscopy, and temperature-dependent photoluminescence measurements. The light output performance of the CdZnO/ZnO QW LED device was also investigated in detail by using I-V and electroluminescence spectral measurements. The characterization showed that our CdZnO/ZnO QW LED structure had good crystalline quality and weaker carrier localization. Owing to the heterojunction structure, the I-V curve indicated that the LED device had a higher turn-on voltage and series resistance. The EL measurement demonstrated that for our LED device’s optoelectronic characteristic, the carrier-screening effect played the dominant role in the emission-energy blue-shift mechanism, and the broadening of the emission energy width was mainly ascribed to the band-filling effect. Without a special heat sinking, the L-I curve exhibited slight efficiency droop after 30 mA.

The effects of N2 carrier gas flow of HCl,NH3 and total N2,the reaction temperature of gallium source and growth temperature on GaN film grown on c-sapphire by hydride vapor phase epitaxy(HVPE) were investigated. The properties of GaN epilayers were characterized by high-resolution X-ray diffraction(HRXRD),Raman spectra and photoluminescence(PL) measurements. The experimental characterizations indicate that the GaN film has good crystal and optoelectronic properties,which has been grown at the optimized N2 carrier gas flow,reaction temperature of gallium source and growth temperature. The measurement results show that the N2 carrier gas flow affects the parasitic reactions,the growth super-saturation of growth front and the transporting of the Ga or N radicals. The optimized growth temperature can enhance the lateral growth and promote the two-dimensional(2D) growth,which benefits the growth of high-quality crystal GaN layer with smooth surface.

In this paper, the processing parameters of growing GaN epilayer by hydride vapor phase epitaxy are optimized The influences of the low-temperature (LT) nucleation layer growth time, WM precursor ratio and the growth temperature on GaN layer are investigated by the high-resolution X-ray diffraction (HRXRD) signature for the asymmetric and symmetric reflections. The investigation finds that the LT-nucleation layer not only supplies the nucleation centers having good crystal quality, but also promotes the lateral growth of the sequent high temperature (HT) growth. The optimal LT nucleation layer growth time, WEI precursor ratio and the growth temperature can effectively enhance lateral growth to reduce the crystal defects and are favorable to converting the growth mechanism from threedimension to two-dimension in HT growth. The structural and optoelectronic properties of the as-grown GaN layer with a thickness of 15 um at the optimal parameters are studied by scanning electron microcopy, atomic force microscopy (AFM), HRXRD, Raman spectra, and photoluminescence (PL) measurements. X-ray rocking curves show that the full widths at half maximum of (002) and (102) are 317 and 343 arcsec, respectively. The surface roughness (rms: root mean square) is 0.334 nm detected using AFM. These characteristics show that the sample has good lattice quality and smooth surface morphology. In PL spectrum, the near band edge emission is dominated by emission from excitons bound to neutral donors (D X) near 3.478 eV with 11 meV blue-shift and the yellow band emission is very weak. The results indicate that the GaN layer has good crystal quality and excellent optoelectronic properties, but a little biaxial in-plane compressive strain also exists in it due to the lattice and thermal mismatch.

A 13.5-pair Al0.98In0.02N/Al0.77Ga0.23N distributed Bragg reflector (DBR) was grown by molecular beam epitaxy on an AlN template substrate. The DBR exhibited a peak reflectivity of 83.9% at 246 nm within the deep solar-blind ultraviolet region and a stopband width of 18 nm. The average refractive index contrast for the DBR was 9.25% at 246 nm, which is relatively high compared with that of a traditional Al(Ga)N/(Al)GaN DBR. Simulated results indicated that a 25.5-pair Al0.98In0.02N/Al0.77Ga0.23N DBR will provide a reflectivity higher than 99% and a 19 nm wide stopband with a center wavelength of 246 nm.

The high crystal quality GaN film has been successfully grown by hydride vapor phase epitaxy (HVPE)and the properties of GaN epilayers have been investigated by high-resolution X-ray diffraction (HRXRD),Raman and photoluminescence (PL)measurements.The temperature dependence of photolumines-cence has been studied particularly.X-ray rocking curves (XRC)showed that the full widths at half maximum (FWHM)of (002 )and (102 )were 322 and 375 arcsec,respectively.Temperature-dependent PL spectra showed that the neutral donor bound excitons (D0 X)emission and free A-excitons recombination peaks reflected the shrinkage of the band gap,but the peak energy and the integrated intensity of 1-longitudinal optical (LO) phonon replica of the free A-excitons exhibited non-monotonic variations with increasing temperature,which might be related to the exciton-polariton dispersion effects of the free excitons caused by gain extra kinetic ener-gy with increasing temperature.HRXRD measurements,Raman and PL spectra all revealed that biaxial in-plane compressive strain (about 0.26 GPa)existed in the GaN layer and the results deduced from the three methods were in good agreement.

In the present paper, strain in GaN epitaxial layer grown by hydride vapor phase epitaxy (HVPE) was investigated by means of high-resolution X-ray diffraction (HRXRD), Raman spectra and photoluminescence (PL) measurements. Both the biaxial in-plane and out-of-plane strains (of the order of -10(-4) and 10(-4), respectively) and the hydrostatic strain component (of the order of -10(-5)) were extracted from HRXRD measurements. These values agreed well with the ones computed from the blue-shift of E2 Raman mode and the near-band-edge PL peak. The results showed that strains in GaN layer were superposed by the biaxial strain and hydrostatic strain.

Taking the final forging microstructure uniformity as optimum objective,the disk isothermal forming process of TC4 alloy is analyzed with combining the virtual experiment and FEM numerical simulation,then the relation between the effective factors of isothermal forging and the function of microstructure uniformity is obtained.Based on the virtual experiment results and FEM numerical simulation,technological parameters of TC4 alloy are optimized by regressive model and simplex method-a kind of optimizing algorithm.Optimizing results indicate that optimizing effect is obvious,and then the results supply a new optimizing viewpoint including virtual experiments,regression model and optimum design for technological parameters of TC4 alloy in isothermal forming process.

A lemniscates micro model is established according to the fabric of the three - dimensional and four-step braided composite . On the base of this model, the distribution of thermal stress and strain of the three-dimensional and four - step composite during the preparation process is analyzed by using FEM software. The effective elastic modulus and the effective thermal expansion coefficient of the three-dimensional and four-step composite at room temperature are simulated and compared with their analytic solution. These results provide an accurate simulation method and give reference to design, process and use this kind of composite.