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.     

镍的金属有机化学气相沉积及相关因素的研究

研究了以碳基镍为沉积源，利用MOCVD技术沉积镍薄膜；讨论了沉积温度及压力对沉积速率的影响，以及利用SEM、XRD、DSC等分析手段来探讨沉积温度及不同沉积基体对薄膜微观形态的影响。结果表明，沉积温度约为150℃可以得到较快的沉积速率，而且薄膜连续具有金属光泽；以铜为沉积基体所得到的薄膜其微观形态中有明显的晶粒，以玻璃为基体得到的薄膜却含有部分非晶态的组织；沉积速率随着反应室工作压力的增加而下降。     

MOCVD的气动控制回路设计

介绍了MOCVD（Metal Organic Chemical Vapor Deposition）液态源金属有机物化学气相沉积设备，研究设计了基于PLC和触摸屏的全自动气动控制回路，实现了对装置中气动元件的自动控制。该方法提高了MOCVD设备的自动化控制水平和安全可靠性，确保了工艺的重复性和稳定性。     

Si Complies with GaN to Overcome Thermal Mismatches for the Heteroepitaxy of Thick GaN on Si

Heteroepitaxial growth of lattice mismatched materials has advanced through the epitaxy of thin coherently strained layers, the strain sharing in virtual and nanoscale substrates, and the growth of thick films with intermediate strain‐relaxed buffer layers. However, the thermal mismatch is not completely resolved in highly mismatched systems such as in GaN‐on‐Si. Here, geometrical effects and surface faceting to dilate thermal stresses at the surface of selectively grown epitaxial GaN layers on Si are exploited. The growth of thick (19 µm), crack‐free, and pure GaN layers on Si with the lowest threading dislocation density of 1.1 × 10⁷ cm^?2 achieved to date in GaN‐on‐Si is demonstrated. With these advances, the first vertical GaN metal–insulator–semiconductor field‐effect transistors on Si substrates with low leakage currents and high on/off ratios paving the way for a cost‐effective high power device paradigm on an Si CMOS platform are demonstrated     

Fabrication and characterization of AlGaN/GaN HEMTs with high power gain and efficiency at 8 GHz

State-of-the-art AlGaN/GaN high electron mobility structures were grown on semi-insulating 4H-SiC substrates by MOCVD and X-band microwave power high electron mobility transistors were fabricated and characterized.Hall mobility of 2291.1 cm2/(V·s) and two-dimensional electron gas density of 9.954 × 1012 cm-2 were achieved at 300 K.The HEMT devices with a 0.45-μm gate length exhibited maximum drain current density as high as 1039.6 mA/mm and peak extrinsic transconduct-ance of 229.7 mS/mm.The fT of 30.89 GHz and fmax of 38.71 GHz were measured on the device.Load-pull measurements were performed and analyzed under (-3.5,28) V,(-3.5,34) V and (-3.5,40) V gate/drain direct current bias in class-AB,respectively.The uncooled device showed high linear power gain of 17.04 dB and high power-added efficiency of 50.56％ at 8 GHz when drain biased at (-3.5,28) V.In addition,when drain biased at (-3.5,40) V,the device exhibited a saturation output power dens-ity up to 6.21 W/mm at 8 GHz,with a power gain of 11.94 dB and a power-added efficiency of 39.56％.Furthermore,the low fmax/fT ratio and the variation of the power sweep of the device at 8 GHz with drain bias voltage were analyzed.     

Remote plasma enhanced metal organic chemical vapor deposition of TiN for diffusion barrier

TiN films were deposited with remote plasma metal organic chemical vapor deposition (MOCVD) from tetrakis-diethyl-amido-titanium (TDEAT) at substrate temperature of 250–500°C and plasma power of 20–80 W. The growth rate using N₂ plasma is slower than that with H₂ plasma and showed 9.33 kcal/mol of activation energy. In the range of 350–400°C., higher crystallinity and surface roughness were observed and resistivity was relatively low. As the temperature increased to 500°C., randomely oriented structure and smooth surface with higher resistivity were obtained. At low deposition temperature, carbon was incorporated as TiC phase, as the deposition temperature increases, carbon was found as hydrocarbon. At 40 W of plasma power, higher crystallinity and rough surface with lower resistivity were obtained and increasing the plasma power to 80 W leads to low crystallinity, smooth surface and higher resistivity. It may be due to the incorporation of hydrocarbon decomposed in the gas phase. Surface roughness was found to be related to the crystallinity of the film.     

GaAs平面掺杂势垒二极管

二极管是定向检波器的重要组件,提高定向检波器的检波灵敏度,需要降低二极管的开启电压.而平面掺杂势垒(PDB)二极管具有极低的势垒高度,适合制作定向检波器.设计了GaAs平面掺杂势垒二极管的材料结构,并采用金属有机化合物气相淀积(MOCVD)方法对其进行外延生长.对PDB二极管的物理模型进行了理论分析.通过模拟计算和实验分析了本征层厚度和p层的面电荷密度对PDB二极管I-V特性的影响.通过实验设计优化了材料结构参数,测试了其I-V特性,使PDB二极管的开启电压降低到了0.06 V,将此样品应用到定向检波器中测得检波灵敏度为20～ 25 mV/mW.     

Microstructure, crystallinity, and properties of low-pressure MOCVD-grown europium oxide films

A study of growth, structure, and properties of Eu₂O₃ thin films were carried out. Films were grown at 500–600 °C temperature range on Si(1 0 0) and fused quartz from the complex of Eu(acac)₃·Phen by low pressure metalorganic chemical vapor deposition technique which has been rarely used for Eu₂O₃ deposition. These films were polycrystalline. Depending on growth conditions and substrates employed, these films had also possessed a parasitic phase. This phase can be removed by post-deposition annealing in oxidizing ambient. Morphology of the films was characterized by well-packed spherical mounds. Optical measurements exhibited that the bandgap of pure Eu₂O₃ phase was 4.4 eV. High frequency 1 MHz capacitance–voltage (C–V) measurements showed that the dielectric constant of pure Eu₂O₃ film was about 12. Possible effects of cation and oxygen deficiency and parasitic phase on the optical and electrical properties of Eu₂O₃ films have been briefly discussed.     

PZT薄膜的MOCVD制备技术

采用直接液体榆运-金属有机化合物化学气相沉积技术（DLI-MOCVD）制备Pb（ZrxTi1-x）O3薄膜（PZT薄膜）,并进行了相关研究,通过调节MOCVD中影响PZT质量的主要工艺参数（温度、压力、系统的气体（Ar,O2）流量、衬底转速、蠕动泵速）,制备不同组分PZT薄膜（均匀性≥±95％,尺寸为2．54—20．32cm（1—8in）,厚度为50—500nm）．经XRD测试可见,PZT薄膜已形成钙钛矿结构．用SEM对其表面进行分析,结果表明,PZT薄膜表面致密均匀．     

蓝宝石衬底上AlGaN外延材料的低压MOCVD生长

采用低温AlN成核层在1180℃温度下在(0001)蓝宝石衬底上用低压MOCVD设备生长了AlGaN外延层.Al组分高达0.6、厚度大于1μm的AlGaN外延层表面光亮,晶体质量较好,(0002)X射线衍射回摆曲线半峰宽FWHM为853弧秒.当反应室气压从5×103Pa降到2×103Pa后, AlGaN 外延层的生长速率和固相Al组分都显著提高.