A viable approach to prepare 3C-SiC coatings by thermal MOCVD using commercial grade precursors

A series of 3 C-SiC coatings were prepared by organometallic chemical vapor deposition (MOCVD) using precursor solution containing a varying proportion of commercial-grade hexamethyldisiloxane (HMDSO) and n-hexane. The phase composition, bonding state, and microstructure of 3 C-SiC coatings were studied in detail by grazing incidence X-ray diffraction (GIXRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The microstructure and mechanical properties of the optimal 3 C-SiC coating were characterized by scanning transmission electron microscopy (STEM) and nanoindentation, respectively. Our results revealed that the amount of undesired graphite phase can be significantly reduced in the 3 C-SiC coating by introducing hydrogen gas in the reaction chamber alongside increasing the ratio of HMDSO/n-hexane in the precursor mixture. The STEM results revealed that the optimal coating was predominantly composed of nano-crystalline 3 C-SiC grains alongside a small amount of amorphous graphite. The hardness and elastic modulus of the optimal coating were 38.19 GPa and 363.2 GPa, respectively.     

MOCVD-derived GdYBCO tapes with smooth surface and low Rs based on a new self-heating technology

The metal organic chemical vapor deposition (MOCVD) method was used to prepare GdYBCO films on LaMnO₃/ homo epitaxial-MgO/ ion-beam-assisted-deposition-MgO/ solution-deposition-planarization-Y₂O₃ buffered Hastelloy tapes. By adopting a simple self-heating technique, the substrates were heated by the joule effect after applying a heating current (I_h) through Hastelloy metal tapes. The effects of substrate temperature and (Gd, Y)/Ba ratio (r_c) in the precursor on the biaxial texture, surface morphology and superconducting performance of GdYBCO films were systematically investigated by varying the values of I_h and r_c. Needle-like outgrowths formed on the substrate surface were characterized using a scanning electron microscope, energy dispersive spectrometer and X-ray diffraction system. The results show that a high I_h or r_c leads to the formation of needle-like outgrowths. Therefore, I_h and r_c are crucial process parameters that control the growth of needle-like outgrowths on the surface of GdYBCO films. Three hundred nanometer thick GdYBCO films were prepared at different I_h and r_c by the MOCVD process. At an I_h of 27.0?A and an r_c of 0.6, the surface of the GdYBCO film was very smooth and dense, which can provide a good template for multiple depositions of GdYBCO films. The critical current density of the deposited 300?nm-thick GdYBCO film was 4.4 MA/cm² (77?K, 0?T), which is attributed to good biaxial texture and appropriate film composition. Furthermore, the microwave surface resistance (77?K, 10?GHz) of the GdYBCO film was merely 0.581?mΩ.     

H2气氛对采用MOCVD 法在Si 衬底上外延生长AlN薄膜性能的影响?

采用金属有机化合物气相沉积法(MOCVD)在 Si(111)衬底上外延生长 AlN 薄膜,用高分辨 X射线衍射、扫描电子显微镜和原子力显微镜对外延生长所得 AlN 薄膜的性能进行表征,并研究了适量H2的引入对 AlN薄膜的晶体结构和表面形貌的影响.结果表明：在 Si衬底上外延生长 AlN薄膜过程中引入适量 H2,有利于提高 AlN岛间愈合程度,薄膜表面缺陷减少,表面粗糙度由4.0 nm 减少至2.1 nm;适量 H2的引入可使 AlN 薄膜的(0002)和(10-12)面的 X 射线摇摆曲线的半峰宽(FWHM)值从0.7°及1.1°分别减小到0.6°和0.9°,即刃型穿透位错密度和螺型穿透位错密度减少.     

掺Si对AlGaInP/GaInP多量子阱发光性能的影响

研究了Si掺杂对MOCVD生长的（Al0.3Ga0.7）In0.5P/Ga0.5In0.5P多量子阱发光性能的影响．样品分为两类：一类只生长了（Al0.3Ga0.7）In0.5P/Ga0.5In0.5P多量子阱结构;另一类为完整的多量子阱LED结构．对于只生长了（Al0.3Ga0.7）In0.5P/Ga0.5In0.5P多量子阱结构的样品,掺Si没有改变量子阱发光波长,但使得量子阱发光强度略有下降,发光峰半高宽明显增大．这应是掺Si使量子阱界面质量变差导致的．而在完整LED结构的情况下,掺Si却大大提高了量子阱的发光强度．相对于未掺杂多量子阱LED结构,垒层掺Si使多量子阱的发光强度提高了13倍,阱层和垒层均掺Si使多量子阱的发光强度提高了28倍,并对这一现象进行了讨论．     

用MOCVD在偏(100)GaAs基片上生长空间规则排列的1.3μm InAs量子点

用MOCVD技术在偏(1100)GaAs衬底上生长了发光波长在1.3μm的线状空间规则排列InAs量子点.光致发光实验表明,相对于正(100)衬底,偏(100)GaAs衬底上生长的InAs量子点具有更好的材料质量,光谱有更大的强度和更窄的线宽.为了得到发光波长为1.3μm的量子点,对比研究了不同In含量的InGaAs应力缓冲层(SBL)和应力盖层(SCL)的应力缓冲作用.结果表明,增加SCL中In含量能有效延伸量子点发光波长到1. 3μm,但是随着SBL中In的增加,发光波长变化不明显,并且材料质量明显下降.     

新型半导体纳米材料的主要制备技术

简要论述了半导体纳米材料的发展历史及其特点,着重讨论了当前国内外主要的几种半导体纳米材料的制备工艺技术,包括溶胶-凝胶法、微乳液法、模板法、基于MBE和MOCVD的纳米材料制备法、激光烧蚀法和应变自组装法等,并分析了以上几种纳米材料制备技术的优缺点及其应用前景.     

Preparation and characterization of single crystalline In2O3 films deposited on MgO (110) substrates by MOCVD

Epitaxial indium oxide (In₂O₃) films have been prepared on MgO (110) substrates by metal-organic chemical vapor deposition (MOCVD). The deposition temperature varies from 500 °C to 700 °C. The films deposited at each temperature display a cube-on-cube orientation relation with respect to the substrate. The In₂O₃ film deposited at 600 °C exhibits the best crystalline quality. A clear epitaxial relationship of In₂O₃ (110)|MgO (110) with In₂O₃ [001]|MgO [001] has been observed from the interface area between the film and the substrate. The average transmittance of the prepared films in the visible range is over 95%. The band gap of the obtained In₂O₃ films is about 3.55–3.70 eV.     

Photocatalytic activity of undoped and sulfur-doped TiO2 films grown by MOCVD for water treatment under visible light

Titanium dioxide ceramic coatings have been used as catalysts in green technologies for water treatment. However, without the presence of a dopant, its photocatalytic activity is limited to the ultraviolet radiation region. The photocatalytic activity and the structural characteristics of undoped and sulfur-doped TiO₂ films grown at 400 °C by metallorganic chemical vapor deposition (MOCVD) were studied. The photocatalytic behavior of the films was evaluated by methyl orange dye degradation under visible light. The results suggested the substitution of Ti⁴⁺ cations by S⁶⁺ ions into TiO₂ structure of the doped samples. SO₄^2? groups were observed on the surface. S-TiO₂ film exhibited good photocatalytic activity under visible light irradiation, and the luminous intensity strongly influences the photocatalytic behavior of the S-TiO₂ films. The results supported the idea that the sulfur-doped TiO₂ films grown by MOCVD may be promising catalysts for water treatment under sunlight or visible light bulbs.     

Study on the structure and properties of core–shell Fe/Al composite powder synthesized by MOCVD in fluidized bed

Core–shell Fe/Al composite powder with different thicknesses of Fe layer has been prepared by MOCVD in a fluidized bed reactor. The products were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDX) and simultaneous thermogravimetry–differential scanning calorimetry (TG–DSC). The results show that a compact nano-Fe layer is covered on the surface of Al to form core–shell Fe/Al composite powder. Nano-Fe layer thickness can be controlled by adjusting deposition time. The Fe layer thickness is evaluated by weight increase in TG curve at the temperature range of 350–550 °C in air atmosphere. Combustion properties of Fe/Al composite powder have great improvement compared with raw Al.     

Heteroepitaxial growth of indium phosphide on silicon by MOCVD using adduct source

Abstract

The heteroepitaxial growth of InP on Si by low pressure metalor‐ganic chemical vapor deposition is reported. Trimethylindium‐trimethylphosphine adduct was used as In source in this study. From X‐ray and SEM examinations, good crystallinity InP epilayers with mirror‐like surfaces can be grown directly on (100) and (111) p‐type Si substrates. Carrier concentration profile shows that the carrier distribution in the InP epilayer is very uniform. The efficient photo‐luminescence compared with that of InP homoepitaxy shows the good quality of InP/Si epilayers.