Influence of hydrogen on SiO2 thick film deposited by PECVD and FHD for silica optical waveguide

Silicon dioxide (SiO₂) thick films have been deposited by plasma enhanced chemical vapor deposition (PECVD) and flame hydrolysis deposition (FHD). PECVD SiO₂ films were obtained at low temperatures (<350 °C) by the decomposition of the appropriate mixture of (SiH₄+N₂O) gases under suitable rf power and N₂O/SiH₄ ratio. For low N₂O/SiH₄ ratio, a refractive index(n) value close to 1.50 is obtained. The deposition rate increased with the increase of rf power. FHD SiO₂ films were produced by the flame hydrolysis reaction of halide materials such as SiCl₄, POCl₃ and BCl₃ in an oxy‐hydrogen torch. The porous SiO₂ layer, under the POCl₃/BCl₃ ratio deposition condition, has to be consolidated by annealing at around 1300 °C.     

射频功率对富硅-氮化硅薄膜结构及性质影响

采用等离子体增强化学气相沉积法,以SiH4、NH3和N2为反应气源,通过改变射频功率制备富硅-氮化硅薄膜材料.利用傅里叶变换红外吸收光谱,紫外-可见光透射光谱,扫描电镜等对薄膜材料结构与性质进行表征.实验表明,随着射频功率的逐渐增加,薄膜光学带隙缓慢减小、有序度增加,薄膜材料中的Si-H键、N-H键缓慢减小,Si-N键增多.分析结果发现,适量的增加射频功率有利于提高样品反应速率,使薄膜有序度增加,致密性增强,提高薄膜质量,但过高的射频功率会使薄膜质量变差.     

An experimental and CFD study on gas flow field distribution in the growth process of multi‐walled carbon nanotube arrays by thermal chemical vapor deposition

Multi‐walled carbon nanotube arrays (MWCNTAs) were grown by thermal chemical vapor deposition (TCVD) in a horizontal furnace reactor. The scanning electron microscopy (SEM) results show that MWCNTAs grown on the bottom and the central of the quartz tube are different in one experiment. Moreover, the MWCNTAs grown on the central position are more aligned and longer than those on the bottom. A computational fluid dynamics (CFD) model was employed to investigate the gas flow field impact on the MWCNTAs growth. The results show that gas circulations appear after carrier gas and carbon source are injected into the quartz tube. Because of the existence of gas circulations, the gas flow field at the central of the quartz tube is more stable, which is conducive to the growth of MWCNTAs. The CFD simulation results match well with the experimental data.     

氩气对直流弧光放电PCVD金刚石薄膜晶体特征的影响

本文采用自主研制的直流弧光放电等离子体CVD设备,在YG6硬质合金基体上进行了不同氩气流量下金刚石薄膜的制备研究.采用SEM对金刚石薄膜的晶体特征进行了观察.结果表明,氩气对直流弧光放电等离子体CVD金刚石薄膜的晶体特征有明显影响.在CH_4/H_2恒定时(0.8;),硬质合金基体上制备的金刚石薄膜表面形貌随Ar流量增加而变化的规律,即从以(111)八面体晶面为主→(111)和(100)立方八面体混杂晶面→以(100)立方体晶面为主→菜花状的顺序转变;当Ar流量为420～700 mL/min时,金刚石晶粒的平均尺寸由1.5 μm 逐步增大到7 μm;Ar流量为700～910 mL/min时,金刚石晶粒的平均尺寸由7 μm急剧减小到纳米尺度,约50 nm.     

Heteroepitaxial growth of Cu2O thin film on ZnO by metal organic chemical vapor deposition

Cuprous oxide (Cu₂O) thin films were grown epitaxially on c-axis-oriented polycrystalline zinc oxide (ZnO) thin films by low-pressure metal organic chemical vapor deposition (MOCVD) from Copper(II) hexafluoroacetylacetonate [Cu(C₅HF₆O₂)₂] at various substrate temperatures, between 250 and 400 °C, and pressures, between 0.6 and 2.1 Torr. Polycrystalline thin films of Cu₂O grow as single phase with [1 1 0] axis aligned perpendicular to the ZnO surface and with in-plane rotational alignment due to (2 2 0)_Cu2O(0 0 0 2)_ZnO; [0 0 1]_Cu2O[1 2¯ 1 0]_ZnO epitaxy. The resulting interface is rectifying and may be suitable for oxide-based p–n junction solar cells or diodes.     

Influence of the substrate temperature on the structural,optical, and electrical properties of tin selenide thin films deposited by thermal evaporation method

Thin films of tin selenide (SnSe) were deposited on sodalime glass substrates, which were held at different temperatures in the range of 350‐550 K, from the pulverized compound material using thermal evaporation method. The effect of substrate temperature (T_s) on the structural, morphological, optical, and electrical properties of the films were investigated using x‐ray diffraction analysis (XRD), scanning electron microscopy (SEM), transmission measurements, and Hall‐effect characterization techniques. The temperature dependence of the resistance of the films was also studied in the temperature range of 80‐330 K. The XRD spectra and the SEM image analyses suggest that the polycrystalline thin films having uniform distribution of grains along the (111) diffraction plane was obtained at all T_s. With the increase of T_s the intensity of the diffraction peaks increased and well‐resolved peaks at 550 K, substrate temperature, were obtained. The analysis of the data of the optical transmission spectra suggests that the films had energy band gap in the range of 1.38‐1.18 eV. Hall‐effect measurements revealed the resistivity of films in the range 112‐20 Ω cm for films deposited at different T_s. The activation energy for films deposited at different T_s was in the range of 0.14 eV‐0.28 eV as derived from the analysis of the data of low‐temperature resistivity measurements. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effects of growth temperature on the properties of ZnO/GaAs prepared by metalorganic chemical vapor deposition

A series of ZnO films were grown on GaAs(0 0 1) substrates at different growth temperatures in the range 250–720°C by metalorganic chemical vapor depostion. Field emission scanning electron microscopy was utilized to investigate the surface morphology of ZnO films. The crystallinity of ZnO films was investigated by the double-crystal X-ray diffractometry. The optical and electrical properties of ZnO films were also investigated using room-temperature photoluminescence and Hall measurements. Arrhenius plots of the growth rate versus reciprocal temperature revealed the kinetically limited growth behavior depending on the growth temperature. It was found that the surface morphology, structural, optical and electrical properties of the films were improved with increasing growth temperature to 650°C. All the properties of the film grown at 720°C were degraded due to the decomposition of ZnO film.     

The photoluminescence of ZnO thin films grown on Si (1 0 0) substrate by plasma-enhanced chemical vapor deposition

High-quality ZnO thin films have been grown on a Si(1 0 0) substrate by plasma-enhanced chemical vapor deposition (PECVD) using a zinc organic source (Zn(C₂H₅)₂) and carbon dioxide (CO₂) gas mixtures at a temperature of 180°C. A strong free exciton emission with a weak defect-band emission in the visible region is observed. The characteristics of photoluminescence (PL) of ZnO, as well as the exciton absorption peak in the absorption spectra, are closely related to the gas flow rate ratio of Zn(C₂H₅)₂ to CO₂. Full-widths at half-maximum of the free exciton emission as narrow as 93.4 meV have been achieved. Based on the temperature dependence of the PL spectra from 83 to 383 K, the exciton binding energy and the transition energy of free excitons at 0 K were estimated to be 59.4 meV and 3.36 eV, respectively.     

Effect of the N/Al ratio of AlN buffer on the crystal properties and stress state of GaN film grown on Si(1 1 1) substrate

The effect of the N/Al ratio of AlN buffers on the optical and crystal quality of GaN films, grown by metalorganic chemical vapor deposition on Si(1 1 1) substrates, has been investigated. By optimizing the N/Al ratio during the AlN buffer, the threading dislocation density and the tensile stress have been decreased. High-resolution X-ray diffraction exhibited a (0 0 0 2) full-width at half-maximum as low as 396 acrsec. The variations of the tensile stress existing in the GaN films were approved by the redshifts of the donor bound exiton peaks in the low-temperature photoluminescence measurement at 77 K.     

沉积时间对Zn(O,S)薄膜性能及Cu2ZnSnSe4薄膜电池的影响

无镉材料Zn(O,S)因其带隙宽且可调节、无毒无害等优点被作为缓冲层材料重点研究,通过化学水浴法制备Zn(O,S)薄膜,研究了沉积时间的不同(20~35 min)对Zn(O,S)薄膜的成分、结构特性、光学性能及形貌的影响.通过XRD测试可知,水浴法制备的Zn(O,S)薄膜为非晶态.通过透反射谱测试可知,薄膜的光学透过率较高(>80;).通过表面形貌测试可知,30 min时Zn(O,S)薄膜为致密均匀的小颗粒.将Zn(O,S)薄膜应用在CZTSe电池中,在30 min时获得较高器件转换效率5.37;.     

Structural,electrical and optical properties of SnO2 films deposited on Y-stabilized ZrO2 (1 0 0) substrates by MOCVD

SnO₂ films have been deposited on Y-stabilized ZrO₂ (YSZ) (1 0 0) substrates at different substrate temperatures (500–800 °C) by metalorganic chemical vapor deposition (MOCVD). Structural, electrical and optical properties of the films have been investigated. The films deposited at 500 and 600 °C are epitaxial SnO₂ films with orthorhombic columbite structure, and the HRTEM analysis shows a clear epitaxial relationship of columbite SnO₂(1 0 0)||YSZ(1 0 0). The films deposited at 700 and 800 °C have mixed-phase structures of rutile and columbite SnO₂. The carrier concentration of the films is in the range from 1.15×10¹⁹ to 2.68×10¹⁹ cm⁻³, and the resistivity is from 2.48×10⁻² to 1.16×10⁻² Ω cm. The absolute average transmittance of the films in the visible range exceeds 90%. The band gap of the obtained SnO₂ films is about 3.75–3.87 eV.     

The influence of the Al pre-deposition on the properties of AlN buffer layer and GaN layer grown on Si (1 1 1) substrate

The influence of Al pre-deposition on the properties of AlN buffer layer and GaN layer grown on Si (1 1 1) substrate by metalorganic chemical vapor deposition (MOCVD) has been systematically studied. Compared with the sample without Al pre-deposition, optimum Al pre-deposition time could improve the AlN buffer layer crystal quality and reduce the root mean square (RMS) roughness. Whereas, overlong Al-deposition time deteriorated the AlN crystal quality and Al-deposition patterns could be found. Cracks and melt-back etching patterns appeared in the GaN layer grown without Al pre-deposition. With suitable Al-deposition time, crack-free 2.0 μm GaN was obtained and the full-width at half-maximum (FWHM) of (0 0 2) plane measured by double crystal X-ray diffraction (DCXRD) was as low as 482 arcsec. However, overlong Al-deposition time would result in a great deal of cracks, and the crystal quality of GaN layer deteriorated. The surface of GaN layer became rough in the region where the Al-deposition patterns were formed due to overlong Al-deposition time.