gamma-LiAlO2 single crystal grown by Czochralski technique and modified by vapor transport equilibration (VTE) technique

Large-sized (similar to 2 inch, 50.8 mm) gamma-UA102 single crystal has been grown by conventional Czochralski (Cz) method, but the crystal ha's a milky, dendriform center. The samples taken from transparent and milky parts were ground and examined by X-ray diffraction. All diffraction peaks could be indexed in gamma-LiAlO2. The crystal quality was characterized by X-ray rocking curve. The full-width at half-maximum (FWHM) values are 116.9 and 132.0 arcsec for transparent and milky parts, respectively. The vapor transport equilibrium (VTE) technique was introduced to modify the crystal quality. After 1000 degrees C/48 h, 1100 degrees C/48 h, 1200 degrees C/48 h VTE processes, the FWHM values dropped to 44.2 and 55.2 arcsec for transparent and milky part, respectively. The optical transmission of transparent part was greatly enhanced from 85% to 90%, and transmission of milky part from 75% to 80% in the range of 190 similar to 1900 nm at room temperature. When the VTE temperature was raised to 1300 degrees C, the sample cracked and FWHM values of transparent and milky parts were increased to 55.2 and 80.9 arcsec, respectively. By combining Cz technique with VTE technique, large-sized and high quality gamma-LiAlO2 crystal can be obtained.

Comparison of ZnO films grown on before- and after-vapor transport equilibration (VTE) LiAlO2 substrates by pulsed laser deposition (PLD)

About Phi 45 mm LiAlO2 single crystal was grown by Czochralski (Cz) technique. However, the full-width at half-maximum (FWHM) value was high to 116.9 arcsec. After three vapor transport equilibration (VTE) processes, we can obtain high-quality LiAlO2 slice with the FWHM value of 44.2 arcsec. ZnO films were fabricated on as-grown slices and after-VTE ones by pulsed laser deposition (PLD). It was found that ZnO films on the two slices have similar crystallinity, optical transmittance and optical band gap at room temperature. These results not only show that LAO substrate is suitable for ZnO growth, but also prove that the crystal quality of LAO substrate slightly affects the structural and optical properties of ZnO film.

Fabrication of beta-BaB2O4 layers on (001) Sr2+-doped alpha-BaB2O4 by vapor transport equilibration (VTE)

Crystalline beta-BBO layers have been successfully prepared on (0 0 1)-oriented Sr2+-doped alpha-BBO substrates using vapor transport equilibration technique. The layers were characterized by X-ray diffraction, X-ray rocking curve and transmission spectra. The present results manifest that the VTE treatment time and powder ratio are important factors on the preparation of beta-BBO layers. beta-BBO layers with a highly (0 0 l) preferred orientation were obtained according to XRD profiles. The full width at half-maximum of the rocking curve for the layer is as low as about 1000 in., which shows the high crystallinity of the layer. These results reveal the possibility of fabricating beta-BBO (0 0 1) layers on (0 0 1)-oriented Sr2+-doped alpha-BBO substrates by VTE. (C) 2006 Elsevier Ltd. All rights reserved.

Structure and residual stress in gamma-LiAlO2, layer fabricated by vapor transport equilibration on (0001)sapphire

gamma-LiAlO2 layers with a highly preferred (1 0 0) orientation were prepared by vapor transport equilibration (VTE) technique on (0 0 0 1) sapphire substrate. Microststructure of the gamma-LiAlO2 layers was studied by XRD and SEM. In the temperature range from 750 to 1100 degrees C, the residual stress in the gamma-LiAlO2 layers varied from tensile to compressive with the increase of VTE temperature, and the critical point of the change between tensile and compressive stress is around 975 degrees C. (c) 2005 Elsevier B.V. All rights reserved.

Composite substrate LiGaO2(001)/beta-Ga2O3(100) fabricated by vapor transport equilibration

Highly (001) orientation LiGaO2 layers have been successfully fabricated on (100) beta-Ga2O3 surface by vapor transport equilibration (VTE) technique. The temperature is very important for the WE treatment. At low temperature (800 degrees C), LiGaO(2)layers are textured. As the temperature was raised to 1100 C the layer becomes highly oriented in the [100] direction. It shows that the best temperature for WE treatment is 1100 degrees C. This technique is promising to fabricate small lattice mismatch composite substrate of LiGaO2 (001)//beta-Ga2O3 (100) for GaN films. (c) 2006 Elsevier B.V. All rights reserved.

Influence of vapor transport equilibration on the crystal quality and thermal-expansion coefficients of gamma-LiAlO2

gamma-LiAlO2 (LAO) single crystal has been grown by the Czochralski method. However, its quality was deteriorated due to lithium volatilization during the crystal growth. The full width at half maximum value drops from 116.9 to 44.2 arc sec after the LAO slice was treated by vapor transport equilibration at 1000, 1100, and 1200 degrees C/48 h in sequence. The treated slice shows higher optical transmission than the as-grown one in the measured wavelength range of 190-1900 nm, meanwhile, its absorption edge exhibits a blueshift. According to Raman spectra, the treated slice has homogeneous quality at different depths from surface to 0.01 mm. The expansion coefficient of the treated slice for a axis drops from 17.2398x10(-6)/degrees C to 16.5240x10(-6)/degrees C, and that for c axis drops from 10.7664x10(-6)/degrees C to 10.0786x10(-6)/degrees C.

用VTE方法在蓝宝石衬底上生长γ-LiAlO2薄膜

利用气相传输平衡技术(VTE)和后退火处理工艺在(0001)蓝宝石衬底上获得了高度[100]取向的γ-LiAlO2薄膜．X射线衍射表明是由单相的γ-LiAlO2所组成,此薄膜经850～900℃／120h空气中退火处理后显示出高度的[100]取向,这一实验结果意味着有望通过VTE方法制备用于GaN基器件外延生长的γ-LiAlO2(100)-Al2O3(0001)复合衬底.

大尺寸高质量γ-LiAlO2晶体的制备研究

采用提拉法快速（6mm／h）生长了透明、φ45mm×50mm完整的铝酸锂晶体，但晶体中下部出现了一个树状、乳白色的核芯．分别从透明和乳白色核芯部位取样，研磨作粉末X射线衍射测试，发现两个样品所有的衍射峰均可以用γ-LiAlO2指标化．双晶摇摆曲线显示晶体透明和乳白色部位的半高宽分别为116．9arcsec和132．0axcsec，结晶质量较差．通过三步气相传输平衡法（简称VTE）处理后，透明部位半高宽值（FWHM）降至44．2arcsec，乳白色部位FWHM值降至53．3arcsec．结合快速生长和VTE

The growth of gamma-LiAlO2 layer with a highly-preferred orientation on (0001) sapphire

Using vapor transport equilibration (VTE) technique we succeeded in the fabrication of single-phase gamma-LiAlO2 layer on (0001) sapphire substrate. X-ray diffraction indicated that the as-fabricated layer was highly textured with [100] orientation at proper VTE treatment temperature range from 1050 degrees C to 1100 degrees C. The main factors affecting the quality of the gamma-LiAlO2 layer were investigated by SEM and transmission spectra. These results reveal the possibility of fabricating gamma-LiAlO2 (100)//sapphire (0001) composite substrate for GaN-based epitaxial film by VTE.

Growth, etching morphology and spectra of LiAlO2 crystal

gamma-LiAlO2 single crystal was successfully grown by Czochralski method. The crystal quality was characterized by X-ray rocking curve and chemical etching. The effects of air-annealing and vapor transport equilibration (VTE) on the crystal quality, etch pits and absorption spectra of LiAlO2 were also investigated in detail. The results show that the as-grown crystal has very high quality with the full width at half maximum (FWHM) of 17.7-22.6 arcsec. Dislocation density in the middle part of the crystal is as low as about 3.0 x 10(3) cm(-2). The VTE-treated slice has larger FWHM value, etch pits density and absorption coefficient as compared with those of untreated and air-annealed slices, which indicates that the crystal quality became inferior after VTE treatment. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Growth of Silicon Carbide Bulk Crystals by Physical Vapor Transport Method and Modeling Efforts in the Process Optimization

Silicon carbide bulk crystals were grown in an induction-heating furnace using the physical vapor transport method. Crystal growth modeling was performed to obtain the required inert gas pressure and temperatures for sufficiently large growth rates. The SiC crystals were expanded by designing a growth chamber having a positive temperature gradient along the growth interface. The obtained 6H-SiC crystals were cut into wafers and characterized by Raman scattering spectroscopy and X-ray diffraction, and the results showed that most parts of the crystals had good crystallographic structures.

Thermoelastic Stresses in SiC Single Crystals Grown by the Physical Vapor Transport Method

A finite element-based thermoelastic anisotropic stress model for hexagonal silicon carbide polytype is developed for the calculation of thermal stresses in SiC crystals grown by the physical vapor transport method. The composite structure of the growing SiC crystal and graphite lid is considered in the model. The thermal expansion match between the crucible lid and SiC crystal is studied for the first time. The influence of thermal stress on the dislocation density and crystal quality is discussed.

Growth of Silicon Carbide Bulk Crystals by Physical Vapor Transport Method and Modeling Efforts in the Process Optimization

Silicon carbide bulk crystals were grown in an induction-heating furnace using the physical vapor transport method. Crystal growth modeling was performed to obtain the required inert gas pressure and temperatures for sufficiently large growth rates. The SiC crystals were expanded by designing a growth chamber having a positive temperature gradient along the growth interface. The obtained 6H-SiC crystals were cut into wafers and characterized by Raman scattering spectroscopy and X-ray diffraction, and the results showed that most parts of the crystals had good crystallographic structures.

气相传输平衡技术制备LiGaO2薄膜

为获得与GaN薄膜晶格失配小的衬底材料，报道了利用气相传输平衡技术（VTE）在（100）β-Ga2O3单晶衬底上制备高度[001]取向LiGaO2薄膜的方法。经过X射线衍射分析表明得到的薄膜是由单相LiGaO2组成。利用扫描电镜（SEM）观察表面形貌，发现经气相传输平衡技术处理得到的薄膜表面形貌主要受温度的影响，表面晶粒尺寸随温度上升而增大。而X射线衍射测试表明随着温度上升，所得到的薄膜也从多晶向单晶化转变。在经过退火处理后，通过观察吸收谱发现LiGaO2薄膜中产生色心，并且色心的种类与温度有关。表明可以

γ-LiAlO2晶体生长、改性和热学性质研究

采用快速提拉法生长出了透明、完整的γ-LIAlO2晶体，但是晶体的高熔点和易挥发性限制了γ-LiAlO2晶体质量．采用气相传输平衡法（vapor transport equilibration technique，VTE）工艺对晶体改性，半高宽（FWHM）值从116．9arcsec降至44．2arcsec，继续升高VTE处理温度至1300℃，FWHM值反而升高至55．2arcsec．快速提拉法生长出来晶体，[100]方向和[001]方向的热膨胀系数分别为17．2398×10^-6／K，10．7664×10