Luminescence of ZnO nanorods grown by chemical vapor deposition on (111) Si substrates

ZnO nanorods have been grown on (111) Si substrates by chemical vapor deposition in a horizontal reactor, with no catalyst. The nanorods grown far from the outlet end of the reactor are larger in size, have a higher structural perfection, and exhibit more efficient room-temperature edge luminescence in comparison with the nanorods grown at the outlet end. The low-temperature cathodoluminescence spectrum of the nanorods also depends on their position in the reactor during growth, which is interpreted in terms of the density of native defects. The nanorods exhibit room-temperature stimulated emission in the excitonic spectral region.     

Ge组分渐变的Si1-x-yGexCy薄膜的制备

用化学气相淀积方法在Si（100）衬底上外延生长了Ge组分最高约0．40的组分渐变的Si1-x-yGexCy合金薄膜,研究了生长温度等工艺参数的影响．结果表明,生长温度和C2H4分压的提高均导致薄膜中碳组分的增加和合金薄膜晶格常数的减小,这表明外延薄膜中的C主要以替位式存在．C掺入量的变化可有效地调节薄膜的禁带宽度,而提高生长温度有助于改善Si1-x-yGexCy薄膜的的晶体质量．组分渐变的Si1-x-yGexCy合金薄膜包括由因衬底中Si原子扩散至表面与GeH4．C2H4反应而生成的Ni1-x-yGexCy外延层和由Ni1-x-yGexCy外延层中Ge原子向衬底方向扩散而形成的Ni1-xGex层．     

Effects of growth variables on the properties of single crystalline ZnO thin film grown by inductively coupled plasma metal organic chemical vapor deposition

Single crystalline undoped and Ga-doped n-type zinc oxide (ZnO) films were grown on sapphire (Al₂O₃) substrates by inductively coupled plasma (ICP) metal organic chemical vapor deposition. Effects of growth variables on the structural, optical, and electrical properties of ZnO films have been studied in detail. Single crystal films with flat and smooth surfaces were reproducibly obtained, with application of sample bias and O₂ ICP. The best film properties were obtained at the growth condition of 650 °C, 400 W ICP power, − 94 V bias voltage, O/Zn (VI/II) ratio of 75. Single crystalline Ga doped n-ZnO films were also obtained, with free carrier concentration of about 1.5 × 10¹⁹/cm³ at 1 at.% Ga concentration.     

Influence of the self-buffer layer on ZnO film grown by atmospheric metal organic chemical vapor deposition

ZnO films with and without a self-buffer layer were grown on c-plane sapphire substrates by atmospheric metal organic chemical vapor deposition. The influence of the buffer layer thickness, annealing temperature and annealing time on ZnO films has been investigated. The full width at half maximum of the ω-rocking curve of the optimized self-buffer layer sample is only 395 arc sec. Its surface is composed of regular columnar hexagons. After the buffer layer was introduced, the A₁ longitudinal mode peak at 576 cm^− 1, related to the defects, disappears in Raman spectra. For the photoluminescence, besides the strong donor binding exciton peak at 3.3564 eV, an ionized donor binding exciton and a free exciton peak is respectively observed at 3.3673 and 3.3756 eV at the high-energy side in the spectrum of the sample with the buffer layer.     

Formation of iron silicide nano-islands on Si substrates by metal organic chemical vapor deposition under electron beams

Electron-beam induced chemical vapor deposition (EBI-CVD) of Fe(CO)₅ was performed on both Si (111) and (110) substrates at 673–873 K inside an ultrahigh vacuum transmission electron microscope. The formation of iron silicide islands was observed on both substrates. Cubic silicide nano-rods were formed on Si(111) substrates by EBI-CVD with focused electron beams. The formation of β-FeSi₂ islands was mainly observed on Si(110) substrates by EBI-CVD when the electron beam was broadly spread. It was shown that the size and the intensity of the electron beam played a significant role in EBI-CVD and affected the CVD process extensively.     

Heteroepitaxial growth of vertical GaAs nanowires on Si(111) substrates by metal-organic chemical vapor deposition

Epitaxial growth of vertical GaAs nanowires on Si(111) substrates is demonstrated by metal-organic chemical vapor deposition via a vapor-liquid-solid growth mechanism. Systematic experiments indicate that substrate pretreatment, pregrowth alloying temperature, and growth temperature are all crucial to vertical epitaxial growth. Nanowire growth rate and morphology can be well controlled by the growth temperature, the metal-organic precursor molar fraction, and the molar V/III ratio. The as-grown GaAs nanowires have a predominantly zinc-blende crystal structure along a <111> direction. Crystallographic {111} stacking faults found perpendicular to the growth axis could be almost eliminated via growth at high V/III ratio and low temperature. Single nanowire field effect transistors based on unintentionally doped GaAs nanowires were fabricated and found to display a strong effect of surface states on their transport properties.     

Photoluminescence and structure of ZnO films deposited on Si substrates by metal-organic chemical vapor deposition

The structure and photoluminescence (PL) at room temperature of ZnO films deposited on Si(111) substrates by metal-organic chemical vapor deposition (MO-CVD) using diethylzinc (DEZ) and CO₂ was investigated. It was found that these properties strongly depend on growth temperature and pressure. ZnO films can be deposited only at low pressure and in the temperature region of 500–650°C. The samples grown at certain conditions can generate stronger luminescence of ZnO. When the growth temperature increased to 650°C, the ZnO₂ phase was observed in X-ray diffraction (XRD) patterns of the samples. This characteristic became evident after the samples annealed. Appearance of a ZnO₂ phase results in production of a new emission band centered at 575 nm in the PL spectrum at room temperature, and the green emitting band also disappears.     

Polycrystalline Si1-x Ge x thin film deposition by rapid thermal chemical vapor deposition

Polycrystalline silicon germanium (poly-Si_1−xGe_x) thin films on a-Si film have been deposited by rapid thermal chemical vapor deposition (RTCVD) with SiH₄–GeH₄–H₂. Effect of GeH₄/SiH₄ and deposition temperature on stoichiometry (x), Si-Ge binding character, composition, hydrogen configuration, crystallinity, preferred orientation, grain size, and surface roughness of poly-Si_1−xGe_x films has been investigated. Poly-Si_1−xGe_x deposited on the substrate with amorphous silicon buffer layer on oxide shows better crystallinity and contains the less amount of oxygen than the one deposited directly on the oxide surface. At low temperature region, the Ge–H bond with the small amount of Si–H₂ bond is dominant but all hydrogen bonds are desorbed at high temperature. All films have polycrystalline phase and the grain size and (111) orientation increased with increasing deposition temperature in which Ge content also increases at the fixed gas flow rate of GeH₄ to total source gas. Poly-Si_1−xGe_x/Si thin film transistors (TFT) are fabricated and hydrogen during post-hydrogenation process preferentially is attached to Ge dangling bond and the TFT characteristics could be improved.     

有机气相沉积中薄膜生长的模拟研究

通过对有机气相沉积中气体的传输过程进行模拟,略述了OVPD传输的基本机制。利用蒙特卡洛法对有机蒸气通过掩膜孔的动力学沉积过程进行仿真,仿真结果表明薄膜的形状受沉积参数的影响,例如,分子平均自由程(沉积压强)、掩膜板的尺寸以及掩膜板至基板的距离。分析表明,通过缩小掩膜板至基板的距离,同时减小沉积压强可以提高所成薄膜图案的分辨率,减小掩膜板的厚度可以提高材料的使用效率。     

Thermally stable transparent conducting and highly infrared reflective Ga-doped ZnO thin films by metal organic chemical vapor deposition

Highly transparent conductive Ga-doped ZnO (GZO) thin films have been prepared on glass substrates by metal organic chemical vapor deposition. The effect of Ga doping on the structural, electrical and optical properties of GZO films has been systematically investigated. Under the optimum Ga doping concentration (∼4.9 at.%), c-axis textured GZO film with the lowest resistivity of 3.6 × 10⁻⁴ Ω cm and high visible transmittance of 90% has been achieved. The film also exhibits low transmittance (<1% at 2500 nm) and high reflectance (>70% at 2500 nm) to the infrared radiation. Furthermore, our developed GZO thin film can well retain the highly transparent conductive performance in oxidation ambient at elevated temperature (up to 500 °C).     

Metal organic chemical vapor deposition and investigation of ZnO thin films grown on sapphire

A new type of large area metal organic chemical vapor deposition (MOCVD) system for the growth of high quality and large size ZnO materials is introduced. Materials properties of the un-doped, n- and p-doped ZnO epi-films grown on sapphire substrates by this MOCVD system are studied by various techniques, including high resolution X-ray diffraction (XRD), UV-Visible optical transmission (OT), photoluminescence (PL) and photoluminescence excitation (PLE), synchrotron radiation X-ray photoelectron spectroscopy (SR-XPS). The wurtzite (w) ZnO crystal structures grown with primary (0002) orientation were identified. Results have shown the high crystalline quality of MOCVD-grown ZnO films, indicated by the narrow XRD, PL and Raman line widths, strong PL signals, sharp OT edge and smooth surface. In particular, high p-type carrier concentration of > 10¹⁷ cm^− 3 have been achieved besides the good n-type doping in ZnO.     

ZnO nanorod arrays grown on glass substrates below glass transition temperature by metalorganic chemical vapor deposition

High density, well-aligned ZnO nanorods with uniform distributions in their diameters and lengths are successfully prepared on amorphous substrates by metalorganic chemical vapor deposition. The X-ray diffraction measurements indicate that the ZnO nanorods are of wurtzite crystal structure, and are grown preferentially on glass substrates along the [0001]_ZnO direction. The degree of the preferred orientation of the ZnO nanorods is enhanced by increasing the growth temperature, as confirmed by the X-ray diffraction and selected area electron diffraction patterns. Photoluminescence investigations revealed the enhancement of the band edge emission with increasing growth temperature, suggesting the improvement in the optical quality of the ZnO nanorods with increasing temperature.     

Phase composition of mixed ZnS-EuS thin films grown by metal organic chemical vapor deposition

The phase composition of the mixed ZnS-EuS films deposited from volatile dithiocarbamates has been studied using differential dissolution technique (chemical method of the phase analysis) and electron microscopy. Phase composition was found to depend on the Eu content in the films, that in turn depends on a flow density ratio of the Eu and Zn volatile precursors. A single-phase solid solution, Zn_0.998Eu_≤0.002S, was observed only for films with Eu content≤1 mol%, other films were found to be two-phase. For films with the Eu content between 2 and 16% and above 80%, impurity phases, EuS and ZnS, respectively, were detected by differential dissolution technique. They evolved as low-sized sulfide precipitates encapsulated in an organic coat. No impurity phases in the films of the same Eu content were noticed by X-ray technique and Raman spectroscopy. For the films with the Eu content between 16 and 80%, sulfide phases, ZnS and EuS, were found to be free from any organic coat, and structural methods as with differential dissolution technique were also capable of observing the phases. Conditions are given to prepare Eu doped ZnS films of good quality by MOCVD technique.     

Transparent conducting indium oxide thin films grown by low-temperature metal organic chemical vapor deposition

We have grown indium oxide thin films on silicon substrates at low temperature by metal organic chemical vapor deposition. Polycrystalline film growth could only be obtained at temperatures below 400 °C. Above 400 °C, metallic indium deposition dominated. We have investigated the effect of substrate temperature and reactor pressure on the film growth and structural properties in the range of 250-350 °C and 5 ^? 10³-4 ^? 10⁴ Pa. The film grown at 300 °C exhibited a resistivity of about 3.6 × 10^− 3 Ω cm and a maximal optical transmittance of more than 95% in the visible range. The film showed an optical band gap of about 3.6 eV.     

Fabrication and characterization of ZnO nanoneedle array using metal organic chemical vapor deposition

High density and vertically well-aligned ZnO nanoneedle arrays were fabricated on the ZnO thin film deposited on silicon substrates. The ZnO buffer layer and nanoneedles were synthesized by metal organic chemical vapor deposition using diethylzinc and oxygen gas. The ZnO buffer film was grown at 250 degrees C and the growth temperature of nanoneedles was in the range of 480-500 degrees C. As-grown ZnO nanoneedles showed single crystalline structure of ZnO (002). The crystalline properties of three samples (A: as-deposited ZnO buffer layer, B: annealed buffer film, C: ZnO nanoneedles) were compared using XRD and Raman spectroscopy. The synthesized ZnO nanoneedles (sample C) showed highest crystalline quality among three samples. The field emission properties of ZnO nanoneedles were investigated, which showed low turn on field of 4.8 Vmicrom(-1) and high field enhancement factor of 3.2 x 103.     

Low temperature growth of SWNTs on a nickel catalyst by thermal chemical vapor deposition

Single-walled carbon nanotubes (SWNTs) have been grown on a silica-supported monometallic nickel (Ni) catalyst at temperatures ranging from as low as 450 °C to 800 °C. Different spectroscopic techniques, such as Raman, photoluminescence emission (PLE), and ultra violet-visible-near infrared (UV-vis-NIR) absorption spectroscopy were used to evaluate the diameter and quality of the SWNTs grown over the Ni catalyst at different temperatures. The analysis revealed that high quality SWNTs with a very narrow diameter distribution were obtained at a growth temperature of 500 °C. In the PLE and absorption spectra, differences were observed between the SWNTs grown on Ni and those grown on cobalt (Co). This result expands the potential of growing a specific (n, m) tube species with relatively high abundance by tuning the catalyst composition. Furthermore, the prerequisites for the low temperature growth of SWNTs over a monometallic transition metal catalyst have been elucidated.      

Preparation of β-Fesi2 thin film by metal organic chemical vapor deposition using iron-carbonyl and mono-silane

β-FeSi₂ films were deposited at 750 °C by a supplying Fe(CO)₅ and SiH₄ simultaneously during metal organic chemical vapor deposition (CVD). Films could be deposited using this precursors system, even though film deposition was not ascertained by the single supply of Fe(CO)₅. Fe(CO)₅ was probably decomposed in gas phases before it reached to substrate surface. It was suggested that a kind of intermediate reactant which was more stable than Fe(CO)₅ created by the simultaneous supply of Fe(CO)₅ and SiH₄ makes Fe-Si films. Epitaxial β-FeSi₂ films were obtained on Si(111) substrates, and neither carbide nor oxide phases were detected on XRD patterns.     

Combinatorial initiated chemical vapor deposition (iCVD) for polymer thin film discovery

Initiated chemical vapor deposition (iCVD) is a technique used to synthesize polymer thin films and coatings from the vapor phase in situ on solid substrates via free-radical mechanisms. It is a solventless, low-temperature process capable of forming very thin conformal layers on complex architectures. By implementing a combinatorial approach that examines five initiation temperatures simultaneously, we have realized at least a five-fold increase in efficiency. The combinatorial films were compared to a series of blanket films deposited over the same conditions to ensure the combinatorial system provided the same information. Direct synthesis from the vapor phase allows for in situ control of film morphology, molecular weight and crosslinking, and the combinatorial system decreases the time required to find the relationship between these interrelated properties. Some coatings were tested for antimicrobial performance against E. coli and B. subtilis.