Microstructures and optical properties of Cu-doped ZnO films prepared by radio frequency reactive magnetron sputtering

Pure and Cu-doped ZnO (ZnO:Cu) thin films were deposited on glass substrates using radio frequency (RF) reactive magnetron sputtering. The effect of substrate temperature on the crystallization behavior and optical properties of the ZnO:Cu films have been studied. The crystal structures, surface morphology and optical properties of the films were systematically investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and a fluorescence spectrophotometer, respectively. The results indicated that ZnO films showed a stronger preferred orientation toward the c-axis and a more uniform grain size after Cu-doping. As for ZnO:Cu films, the full width at half maxima (FWHM) of (0 0 2) diffraction peaks decreased first and then increased, reaching a minimum of about 0.42° at 350 °C and the compressive stress of ZnO:Cu decreased gradually with the increase of substrate temperature. The photoluminescence (PL) spectra measured at room temperature revealed two blue and two green emissions. Intense blue-green luminescence was obtained from the sample deposited at higher substrate temperature. Finally, we discussed the influence of annealing temperature on the structural and optical properties of ZnO:Cu films. The quality of ZnO:Cu film was markedly improved and the intensity of blue peak (∼485 nm) and green peak (∼527 nm) increased noticeably after annealing. The origin of these emissions was discussed.     

Structure, morphology and properties of Fe-doped ZnO films prepared by facing-target magnetron sputtering system

We have prepared a series of ZnO films with various concentrations of Fe dopant by using facing-target magnetron sputtering system and investigated their structure, morphology, optical properties and magnetic properties by means of the X-ray diffraction, Raman spectrometer, X-ray photoelectron spectroscopy, scanning electron microscope, UV-vis spectrophotometer, spectrofluorophotometer and vibrated sample magnetometer, respectively. The results showed Fe was in 2+ valence state in film. With increasing the concentration of Fe dopant the crystal quality deteriorated gradually and an increasing compressive stress occurred in ZnO films. All the grains grew with a columnar form along the [0 0 2] direction and the average size of grains decreased monotonically as the concentration of Fe dopant increased. The calculated results indicated that the band gap of films decreased with the increment of the concentration of Fe dopant, which resulted in the red-shift of violet emission peak. Moreover, the intensity of violet emission peak increased with the increment of Fe concentration because of the interface trap existing in depletion regions located at the ZnO grains boundaries. When the concentration of Fe dopant was smaller than 0.028, the films exhibited paramagnetic properties while the films displayed weak ferromagnetic properties when the concentration of Fe dopant increased to 0.041.     

As-doped p-type ZnO films grown on SiO2/Si by radio frequency magnetron sputtering

p-Type ZnO:As films with a hole concentration of 10¹⁶-10¹⁷ cm⁻³ and a mobility of 1.32-6.08 cm²/V s have been deposited on SiO₂/Si substrates by magnetron sputtering. XRD, SEM, Hall measurements are used to investigate the structural and electrical properties of the films. A p-n homojunction comprising an undoped ZnO layer and a ZnO:As layer exhibits a typical rectifying behavior. Our study demonstrates a simple method to fabricate reproducible p-type ZnO film on the SiO₂/Si substrate for the development of ZnO-based optoelectronic devices on Si-based substrates.     

Preparation of boron carbon nitride thin films by radio frequency magnetron sputtering

Boron carbon nitride films were deposited by radio frequency magnetron sputtering using a composite target consisting of h-BN and graphite in an Ar-N₂ gas mixture. The samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The results suggest that the films are atomic-level hybrids composed of B, C and N atoms. The boron carbon nitride films prepared in the present experiment have a disordered structure. The sputtering power varied from 80 W to 130 W. This sputtering power was shown to have regular effect on the composition of boron carbon nitride films. The samples deposited at 80 W and 130 W are close to the stoichiometry of BC₃N. The sample deposited at 110 W is close to the stoichiometry of BCN. The samples deposited at 100 W and 120 W approach to BC₂N. It is very significant for us to synthesize boron carbon nitride compound with controllable composition by changing the sputtering power.     

Synthesis and characterization of porous crystalline SiC thin films prepared by radio frequency reactive magnetron sputtering technique

Hexagonal SiC thin films have been deposited using radio frequency reactive magnetron sputtering technique by varying the substrate temperature and other deposition conditions. Prior to deposition surface modification of the substrate Si(1 0 0) played an important role in deposition of the hexagonal SiC structure. The effect of substrate temperature during deposition on structure, composition and surface morphology of the SiC films has been analyzed using atomic force microscopy, Fourier transform infrared spectroscopy and spectroscopic ellipsometry. X-ray diffraction in conventional θ-2θ mode and omega scan mode revealed that the deposited films were crystalline having 8H-SiC structure and crystallinity improved with increase of deposition temperature. The bonding order and Si-C composition within the films showed improvement with the increase of deposition temperature. The surface of thin films grew in the shape of globes and columns depending upon deposition temperature. The optical properties also showed improvement with increase of deposition temperature and the results obtained by ellipsometry reinforced the results of other techniques.     

Field emission from ZnS nanorods synthesized by radio frequency magnetron sputtering technique

The field emission property of zinc sulphides nanorods synthesized in the thin film form on Si substrates has been studied. It is seen that ZnS nanorod thin films showed good field emission properties with a low-macroscopic turn-on field (2.9-6.3 V/μm). ZnS nanorods were synthesized by using radio frequency magnetron sputtering of a polycrystalline prefabricated ZnS target at a relatively higher pressure (10⁻¹ mbar) and at a lower substrate temperature (233-273 K) without using any catalyst. Transmission electron microscopic image showed the formation of ZnS nanorods with high aspect ratio (>60). The field emission data were analysed using Fowler-Nordhiem theory and the nearly straight-line nature of the F-N plots confirmed cold field emission of electrons. It was also found that the turn-on field decreased with the decrease of nanorod's diameters. The optical properties of the ZnS nanorods were also studied. From the measurements of transmittance of the films deposited on glass substrates, the direct allowed bandgap values have been calculated and they were in the range 3.83-4.03 eV. The thickness of the films was ∼600 nm.     

Surface morphology of ZnO buffer layer and its effects on the growth of GaN films on Si substrates by magnetron sputtering

ZnO thin films were first prepared on Si(111) substrates using a radio frequency magnetron sputtering system. Then the as-grown ZnO films were annealed in oxygen ambient at temperatures of 700, 800, 900, and 1000°C , respectively. The morphologies of ZnO films were studied by an atom force microscope (AFM). Subsequently, GaN epilayers about 500 nm thick were deposited on the ZnO buffer layers. The GaN/ZnO films were annealed in NH₃ ambient at 900°C. The microstructure, morphology and optical properties of GaN films were studied by x-ray diffraction (XRD), AFM, scanning electron microscopy (SEM) and photoluminescence (PL). The results are shown, their properties having been investigated particularly as a function of the ZnO layers. For better growth of the GaN films, the optimal annealing temperature of the ZnO buffer layers was 900°C.     

Photoluminescence of a ZnO/GaN Heterostructure Interface

Growth of a ZnO/GaN heterostructure is carried out using pulsed laser deposition. By etching the ZnO layer from the ZnO/GaN structure, the photoluminescence （PL） of the associated GaN layer shows that the donor- acceptor luminescence of CaN shifts to about 3.27eV, which is consistent with the electroluminescence （EL） of n-ZnO/p-GaN already reported. XPS shows that oxygen diffuses into the CaN crystal lattice from the surface to 20nm depth. The PL spectra at different temperatures and excitation densities show that oxygen plays the role of potential fluctuation. The associated PL results of the interface in these LEDs could be helpful to understand the mechanism of EL spectra for ZnO/CaN p-n junctions.     

Photoluminescence and Raman scattering of Cu-doped ZnO films prepared by magnetron sputtering

The Cu-doped ZnO films were prepared by direct current reactive magnetron sputtering using a zinc target with various Cu-chips attached. The influences of Cu-doping on the microstructure, photoluminescence, and Raman scattering of ZnO films were systematically investigated. The results indicate that ZnO films doped with moderate Cu dopant (2.0-4.4 at.%) can obtain wurtzite structure with strong c-axis orientation. The near band edge (NBE) emission of ZnO film can be enhanced by Cu dopant with a concentration of 2.0 at.% and quench quickly with further increase of doping concentration. Two additional modes at about 230 and 575 cm⁻¹, which could be induced by Cu dopant, can be observed in Raman spectra of the Cu-doped ZnO films.     

GaN films deposited by middle-frequency magnetron sputtering

GaN films were deposited on Si (111) substrates by middle-frequency magnetron sputtering. X-ray diffraction revealed preferential GaN (0 0 0 2) orientation normal to the substrate surface for all the films deposited. The diffraction intensity and N contents were found to depend strongly on the total gas pressure. Good quality films were only obtained at pressures in the range of 0.4-1.0 Pa. Little diffraction of GaN (0 0 0 2) could be observed either at total pressures below 0.4 Pa or above 1.0 Pa. The GaN films produced under the optimized conditions have an N:Ga ratio of 1:1 as determined by energy-dispersive X-ray spectroscopy.     

Effects of the sputtering time of ZnO buffer layer on the quality of GaN thin films

ZnO thin films with different thickness (the sputtering time of ZnO buffer layers was 10 min, 15 min, 20 min, and 25 min, respectively) were first prepared on Si substrates using radio frequency magnetron sputtering system and then the samples were annealed at 900 °C in oxygen ambient. Subsequently, a GaN epilayer about 500 nm thick was deposited on ZnO buffer layer. The GaN/ZnO films were annealed in NH₃ ambient at 950 °C. X-ray diffraction (XRD), atom force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) were used to analyze the structure, morphology, composition and optical properties of GaN films. The results show that their properties are investigated particularly as a function of the sputtering time of ZnO layers. For the better growth of GaN films, the optimal sputtering time is 15 min.     

Controlled visible photoluminescence of ZnO thin films prepared by RF magnetron sputtering

ZnO thin films were prepared by RF magnetron sputtering. The photoluminescence dependence on the growth ambient and annealing temperatures and the atmosphere has been studied. Visible photoluminescence with blue, green, orange, and red emission bands has been demonstrated by controlling the preparation conditions. Complete suppression of the visible emission bands was also realized by annealing the O₂-ambient-grown samples in N₂ atmosphere at higher temperatures, which indicated the preparation of ZnO thin films with high optical quality.     

Surface oxidation of vanadium dioxide films prepared by radio frequency magnetron sputtering

This paper reports that the thermochromic vanadium dioxide films were deposited on various transparent substrates by radio frequency magnetron sputtering, and then aged under circumstance for years. Samples were characterized with several different techniques such as x-ray diffraction, x-ray photoelectron spectroscopy, and Raman, when they were fresh from sputter chamber and aged after years, respectively, in order to determine their structure and composition. It finds that a small amount of sodium occurred on the surface of vanadium dioxide films, which was probably due to sodium ion diffusion from soda-lime glass when sputtering was performed at high substrate temperature. It also finds that aging for years significantly affected the nonstoichiometry of vanadium dioxide films, thus inducing much change in Raman modes.     

Structural and Optical Properties of Zinc Nitride Films Prepared by Pulsed Filtered Cathodic Vacuum Arc Deposition

Polycrystalline zinc nitride films are deposited on Coming 7059 glass substrates by pulsed filtered cathodic vacuum arc deposition （PFCVAD）. The crystallographic structure is studied by means of x-ray diffraction. These measurements show that all the films are crystallized in the cubic structure, in a preferred orientation along the （332） and （631） directions. Weak XRD signal shows small crystallites distributed in an amorphous tissue. A small improvement of crystallinity is observed with annealing. Optical parameters such as absorption, energy band gap, Urbach tail, extinction coefficients have been determined. The Urbach tail energy is decreased with annealing at 500℃ for one hour. Energy band gap values are found to be increased by annealing.     

磁控溅射法制备金团簇纳米颗粒及性能表征

 采用磁控溅射法制备金团簇纳米颗粒,用透射电镜(TEM)、X射线衍射(XRD)、紫外可见光分光光度计(UV-Vis)和X射线光电子能谱(XPS)等分析手段对其表征,研究了金团簇纳米颗粒的形貌、颗粒度、结构、光吸收性质及物质成份。研究结果表明：制备的金团簇纳米颗粒呈球形,平均粒径在10 nm左右,粒径分布均匀,无团聚、氧化现象,颗粒的结构为面心立方。在519 nm处出现团簇颗粒的表面等离子共振吸收峰,测试得到Au(4f_7/2)和Au(4f_5/2)电子的结合能分别为83.3 eV和86.9 eV,并且没有出现金的氧化产物。     

磁控溅射法制备金团簇纳米颗粒及性能表征

采用磁控溅射法制备金团簇纳米颗粒,用透射电镜(TEM)、X射线衍射(XRD)、紫外可见光分光光度计(UV-Vis)和X射线光电子能谱(XPS)等分析手段对其表征,研究了金团簇纳米颗粒的形貌、颗粒度、结构、光吸收性质及物质成份。研究结果表明：制备的金团簇纳米颗粒呈球形,平均粒径在10 nm左右,粒径分布均匀,无团聚、氧化现象,颗粒的结构为面心立方。在519 nm处出现团簇颗粒的表面等离子共振吸收峰,测试得到Au(4f7/2)和Au(4f5/2)电子的结合能分别为83.3 eV和86.9 eV,并且没有出现金的氧化产物。     

用射频溅射法制备立方氮化硼薄膜

利用射频溅射方法在n型Si(111)衬底上制备出立方相含量接近100%且粘附性较高的立方氮化硼(c-BN)薄膜.傅里叶变换红外谱(FTIR)的结果表明，基底负偏压对薄膜立方相含量和薄膜压应力有很大影响，另外，衬底的电阻率对c-BN生长和薄膜的压应力也有一定的影响. 关键词： 立方氮化硼 射频溅射 压应力 基底负偏压     

Photoluminescence study of manganese in AlSb

We have investigated Czochralski-grown manganese-doped AlSb by low-temperature photoluminescence spectroscopy. Discrete donor-acceptor pair lines are resolved, which involve the Mn acceptor. A Mn acceptor binding energy (E _A =92±5 meV) is deduced from the donor-acceptor pair luminescence.     

Near band-edge luminescence of semi-insulating undoped gallium arsenide at high levels of excitation

The dependences of the maximum and the half-width of near band-edge photoluminescence of semi-insulating undoped-GaAs crystals at 77 K on the concentration of background acceptor impurities and the level of excitation in the range from 3×10²¹ to 6×10²² quantum/(cm² s) are investigated. The observed dependences are explained by formation of the density tails of states as a result of fluctuations of impurity concentration and participation of localized states of the donor impurity band in radiative transitions. Reduction of many-particle interaction at increasing of N can be connected with increasing of shielding of charge carriers by atoms of impurity.     

射频反应磁控溅射法制备的氟化类金刚石薄膜摩擦特性研究

以高纯石墨做靶,CHF3和Ar气为源气体,采用射频反应磁控溅射法在不同流量比条件下制备了氟化类金刚石(F-DLC)薄膜.利用原子力显微镜、纳米压痕仪、拉曼光谱和红外光谱、摩擦磨损测试仪对薄膜的表面形貌、硬度、键结构以及摩擦性能做了具体分析.表面形貌测试结果表明,制备的薄膜整体均匀致密,表现出了良好的减摩性能.当CHF3与Ar气流量比r为1:6时,所得薄膜的摩擦系数减小至0.42,而纳米压痕结果显示,此时薄膜的硬度也最高.拉曼和红外光谱显示,随着r的增加,薄膜中的F浓度呈上升趋势,薄膜中的芳香环比例减小.研究表明,F原子的键入方式是影响F-DLC薄膜摩擦系数的一个重要因素,CF2反对称伸缩振动强度的减弱和CC中适量碳氢氟键的形成都能导致薄膜具有相对较低的摩擦系数.