Annealing effect on the photoluminescence of Si nanocrystallites thin films

Si nanocrystallites thin films on p-type (100) Si substrate have been fabricated by pulsed laser deposition (PLD) using a Nd:YAG laser.After deposition, samples were annealed in several environmental gases at the temperature range from 400 to 800 °C. Strong violet-indigo photoluminescence has been observed at room temperature (RT) from nitrogen ambient-annealed Si nanocrystallites. The variation of photoluminescence (PL) properties of Si nanocrystallites thin films has been investigated depending on annealing temperatures. As the results of PL and high-resolution transmission electron microscope (HRTEM) measurements, we could suggest that the origin of violet-indigo PL from the films was related to the quantum size effect of Si nanocrystallites.     

Annealing effect on properties of transparent and conducting ZnO thin films

This work presents the effect of postdeposition annealing on the structural, electrical and optical properties of undoped ZnO (zinc oxide) thin films, prepared by radio-frequency sputtering method. Two samples, 0.17 and 0.32 µm-thick, were annealed in vacuum from room temperature to 350 °C while another 0.32 µm-thick sample was annealed in air at 300 °C for 1 h. X-ray diffraction analysis revealed that all the films had a c-axis orientation of the wurtzite structure normal to the substrate. Electrical measurements showed that the resistivity of samples annealed in vacuum decreased gradually with the increase of annealing temperature. For the 0.32 µm-thick sample, the gradual decrease of the resistivity was essentially due to a gradual increase in the mobility. On the other hand, the resistivity of the sample annealed in air increased strongly. The average transmission within the visible wavelength region for all films was higher than 80%. The band gap of samples annealed in vacuum increased whereas the band gap of the one annealed in air decreased. The main changes observed in all samples of this study were explained in terms of the effect of oxygen chemisorption and microstructural properties.     

微孔状ZnO薄膜的生长与光致发光性

使用Zn（CH3COO）2·2H2O和PVA水溶液混合的办法在Si衬底上生长了微孔结构的ZnO薄膜。样品的晶体结构、形貌及光致发光性使用XRD、SEM及PL谱进行表征。结果表明所制备的ZnO为六方纤锌矿型晶体结构，微孔的孔壁是由纳米颗粒聚集而成，颗粒尺寸大约为20nm,关于这种结构的形成，我们推测PVA在微孔结构的形成过程中起到了模板作用。     

Study on the Hall-effect and photoluminescence of N-doped p-type ZnO thin films

N-doped, p-type ZnO thin films have been grown by plasma-assisted metal-organic chemical vapor deposition method. The results under optimized growth conditions included a resistivity of 1.72 Ω cm, a Hall mobility of 1.59 cm²/V s, and a hole concentration of 2.29 × 10¹⁸ cm^− 3, and were consistently reproducible. A N-related free-to-neutral-acceptor emission and an associated phonon replica were evident in room temperature photoluminescence spectra, from which the N acceptor energy level in ZnO was estimated to be 180 meV above the valence band maximum.     

Effects of oxygen pressure on the structure and photoluminescence of ZnO thin films

A series of ZnO thin films were deposited on silicon (100) substrate at 473 K by using facing target RF magnetron sputtering system at different oxygen pressure in this paper. The structure, surface morphology and photoluminescence of the ZnO thin films were characterized by X-ray diffraction, atomic force microscopy (AFM), and photoluminescence spectra (PL), respectively. The results showed that only a (002) peak of hexagonal wurtzite appeared in all ZnO thin films, indicating that ZnO films exhibited strong texture. With increasing the oxygen pressure, the results indicated that the ZnO film deposited at 1.2 Pa Ar pressure and 0.6 Pa oxygen pressure had the best preferential C-axis orientation and the weakest compressive stress. Meanwhile, AFM observation showed that ZnO film deposited at pure Ar had the highest surface roughness. With the increment of oxygen pressure, the surface roughness decreased gradually. In addition, PL measurement showed that the ZnO film deposited at 1.2 Pa Ar pressure and 0.6 Pa oxygen pressure had the strongest ultraviolet emission and the weakest blue emission.     

Optical and photoluminescence studies of gold nanoparticles embedded ZnO thin films

Gold nanoparticles (AuNPs) embedded ZnO thin films were prepared by sandwiching a thin thermally evaporated Au film between two sputtered ZnO films. The films were characterized by high resolution transmission electron microscopy (HRTEM), glancing angle X-ray diffraction (GXRD), optical absorption and photoluminescence (PL) measurements. GXRD data exhibited peaks which were attributed to the reflections from various ZnO and Au planes. Size dependence of the plasmon absorption was studied by forming nanoparticles with various sizes. Optical absorption spectra showed strong absorption due to localized surface plasmons at about 608, 638 and 676 nm for films having average AuNPs sizes of 27, 40 and 67 nm respectively. AuNPs embedded ZnO film showed a strong reduction in the intensity of photoluminescence, which was prominent in the case of pure ZnO film. The rise in temperature at a single nanoparticle site was calculated to be 22 K for a particle size of 80 nm.     

ZnO薄膜的塞贝克效应

采用直流反应磁控溅射方法在玻璃基底上成功地沉积了C轴取向性能良好的ZnO薄膜.本文研究了C轴取向性良好的ZnO薄膜在光学方面的一些性质以及ZnO薄膜的塞贝克效应,并从理论上进行了分析.     

Correlation between film quality and photoluminescence in sputtered ZnO thin films

A red photoluminescence (PL) is observed in as-deposited ZnO thin films which are prepared by a conventional sputtering method. The PL intensity strongly depends on sputtering deposition conditions. In as-deposited and annealed films, it is found that there exists a correlation between the red PL intensity and the film quality. The origin of the red PL is attributed to the native defect induced during the sputtering deposition process. It is shown that the red PL measurement is effective as an evaluation method of the film quality.     

Preparation of Li and Er codoped ZnO thin films and their photoluminescence

Li-Er codoped ZnO thin films have been prepared on Si(100) substrates by pulsed laser deposition (PLD). Both the as-grown and post-annealed films exhibit good crystalline quality with preferred c-axis orientation. After post-annealing at 850 °C, the photoluminescence (PL) related to intra-4f shell of Er³⁺ can be clearly observed. The Li-Er codoped ZnO film shows higher intensity of PL around 1.54 μm than the Er monodoped ZnO film. The behavior is attributed to the lowering of the symmetry of the crystal field around Er³⁺ ions by introducing Li⁺ into ZnO lattice, which is also confirmed by Raman scattering spectra.     

磁控溅射制备ZnO:Eu薄膜发光性能研究

采用射频磁控溅射法在蓝宝石基片上制备ZnO:Eu薄膜,通过X射线衍射仪和荧光分光光度计等测试其晶体结构和发光特性,分析退火对薄膜晶体结构和发光特性的影响.结果表明,ZnO:Eu薄膜为C轴择优生长的多晶薄膜,实现ZnO基质中掺杂Eu3+;退火样品结晶质量较好,有助于ZnO:Eu薄膜中Eu3+的5D0-7F2的能级跃迁发光;高于ZnO带隙的高能激发(间接激发)和Eu3+的7F0-5L6和7F3-5D2能级间的低能共振激发(直接激发)都能观察到Eu3+的5D0-7F2能级跃迁的特征发光(618nm);间接激发时存在ZnO基质与Eu3之间发生能量传递.     

Annealing effect of ZnO/Au/ZnO transparent conductive films

Au intermediate ZnO (ZAZ) thin films were prepared by radio frequency and direct current magnetron sputtering on glass substrates and then vacuum annealed. The thickness of each layer of the ZAZ films was set at 50 nm, 3 nm, and 47 nm, respectively. The structural, electrical, and optical properties of ZAZ films were investigated with respect to the variation of annealing temperature.As-deposited AZO films showed X-ray diffraction peaks corresponding to ZnO (002) and Au (111) planes and those peak intensities increased with post-deposition vacuum annealing. The optical and electrical properties of the films were strongly influenced by post-deposition annealing. Although the optical transmittance of the films deteriorated with an Au interlayer, as-deposited ZAZ films showed a low resistivity of 2.0 × 10⁻⁴ Ω cm, and the films annealed at 300 °C had a lower resistivity of 9.8 × 10⁻⁵ Ω cm. The work function of the films increased with annealing temperature, and the films annealed at 300 °C had a higher work function of 4.1 eV than the films annealed at 150 °C. The experimental results indicate that vacuum-annealed ZAZ films are attractive candidates for use as transparent electrodes in large area electronic applications such as solar cells and large area displays.     

Effect of the oxygen pressure on the photoluminescence properties of ZnO thin films by PLD

ZnO thin films on Si(111) substrate were deposited by laser ablation of Zn target in oxygen reactive atmosphere; Nd-YAG laser with wavelength of 1064 nm was used as laser source. The experiments were performed at laser energy density of 31 J/cm², substrate temperature of 400 °C and various oxygen pressures (5–65 Pa). X-ray diffraction was applied to characterize the structure of the deposited ZnO films and the optical properties of the ZnO thin films were characterized by photoluminescence with an Ar ion laser as a light source using an excitation wavelength of 325 nm. The influence of the oxygen pressure on the structural and optical properties of ZnO thin films was investigated. It was found that ZnO film with random growth grains can be obtained under the condition of oxygen pressure 5–65 Pa. It will be clearly shown that the grain size and the formation of intrinsic defects depend on the oxygen partial pressure and that high optical quality of the ZnO films is obtained under low oxygen pressure (5 Pa, 11 Pa) conditions.     

Pulsed laser deposition and photoluminescence measurements of ZnO thin films on flexible polyimide substrates

In order to assess the potential of zinc oxide (ZnO) in flexible electronics applications, we created continuous ZnO films on polymeric substrates for evaluation of structural and optical properties. Specifically, we have used pulsed laser deposition to deposit ZnO films with thickness of several microns on flexible free-standing polyimide substrates. A KrF excimer laser (248 nm) operated at fluences of 3.0-6.2 J/cm² was used. ZnO films were deposited at temperatures between room temperature and 300 °C under O₂ atmosphere at a pressure of 50 Pa. Good flexibility characterizes the obtained layers and X-ray diffraction measurements show that films present all reflections of hexagonal ZnO. We discuss luminescence measurements on the films in relation to the complex interface phenomena expected in our samples.     

Studies on the seebeck effect in semiconducting ZnO thin films

For ZnO thin films prepared by a pyrolytic technique, the thermoelectric power has been measured from room temperature up to 200 °C with reference to pure lead. The thickness and temperature dependence of its related parameters have been studied. The Fermi levels were determined using a nondegenerate semiconducting model. The carrier scattering index, activation energy and temperature coefficient of activation energy, have all been obtained at different ranges of thickness and temperature. All the samples were polycrystalline in structure and optically transparent.     

衬底温度对N-Al共掺杂ZnO薄膜形貌及光致发光性能的影响

采用超声喷雾热解法在不同衬底温度条件下沉积了N-Al共掺杂ZnO薄膜,衬底为普通硅酸盐玻璃。利用X射线衍射仪、原子力显微镜和荧光光谱仪表征了样品的晶体结构、形貌及室温光致发光性能。结果表明,ZnO颗粒尺寸随着衬底温度的升高而逐渐增大;低温下沉积的样品发光光谱中缺陷发射光占主导,随着衬底温度的升高这些缺陷发射光强度逐渐减弱,当温度升高到450℃时只有紫外发射光。缺陷发射光强度的减弱意味着薄膜缺陷浓度减小、晶体趋于完整,同时反映出施主型缺陷浓度随衬底温度的升高而逐渐减小,这对减弱ZnO薄膜p型掺杂时Vo或Zni等施主缺陷的自补偿效应很有意义。     

Influence of vanadium concentration on the microstructure and magnetic properties of V-doped ZnO thin films

Vanadium doped ZnO thin films (Zn_1 − xV_xO, where x = 0.05 or x = 0.13) were grown on c-cut sapphire substrates using pulsed laser deposition technique. Their structure and magnetic properties were examined in relation to the doping concentration. All deposited films were highly oriented along the c-axis and exhibited ferromagnetic behavior with a Curie temperature up to 300 K. The crystal structure was found to be better for layers with lower vanadium concentration. The films had a porous fine-grained microstructure and a column-like character as the V concentration was reduced. A weak dependence of magnetization on temperature was observed. The saturation magnetization was found to be strongly dependent on the crystal structure, grain size and V-ion concentration.     

退火温度对RF磁控溅射ZnO薄膜力学性能的影响

采用X射线衍射分析(XRD),原子力显微镜(AFM)及纳米压痕技术测试分析了多晶ZnO薄膜的晶格结构和力学性能.薄膜的制备采用了射频(RF)磁控溅射方法,并分别在不同温度下进行了退火处理.XRD分析显示随着退火温度的上升,薄膜的晶粒尺寸逐步增大,且C轴取向显著增强.压痕测试结果表明,由于尺寸效应的影响,硬度随退火温度的变化有明显的趋势,从2.5GPa(常温下)逐步增加到5.5GPa(4500C),随着温度的进一步上升,硬度值又逐步下降到4.5GPa(650℃).弹性模量整体随退火温度的变化并不呈现明显的规律,但在450℃和200℃下退火分别有最大值26.7GPa和最小值21.5GPa,这是由于尺寸效应与晶格取向的双重作用的结果.测试结果表明适当的退火处理对ZnO薄膜的结晶品质与力学性能有明显的改善.     

Influence of Nd dopant amount on microstructure and photoluminescence of TiO2:Nd thin films

TiO₂ and TiO₂:Nd thin films were deposited using reactive magnetron sputtering process from mosaic Ti–Nd targets with various Nd concentration. The thin films were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM) and spectroscopic techniques. Photoluminescence (PL) in the near infrared obtained upon 514.5 nm excitation was also examined. The relationship between the Nd concentration, structural, optical and photoluminescence properties of prepared thin films was investigated and discussed. XRD and TEM measurements showed that an increase in the Nd concentration in the thin films hinders the crystal growth in the deposited coatings. Depending on the Nd amount in the thin films, TiO₂ with the rutile, mixed rutile–amorphous or amorphous phase was obtained. Transmittance measurements revealed that addition of Nd dopant to titania matrix did not deteriorate optical transparency of the coatings, however it influenced on the position of the fundamental absorption edge and therefore on the width of optical band gap energy. All TiO₂:Nd thin films exhibited PL emission that occurred at ca. 0.91, 1.09 and 1.38 μm. Finally, results obtained for deposited coatings showed that titania with the rutile structure and 1.0 at.% of Nd was the most efficient in VIS to NIR photon conversion.     

Low temperature photoluminescence and infrared dielectric functions of pulsed laser deposited ZnO thin films on silicon

C-axis oriented ZnO thin films were grown on silicon (100) and (111) substrates by pulsed laser deposition. Low temperature photoluminescence spectra show besides the peaks of free excitons, of defect bound excitons, and of a donor-acceptor pair transition a new doublet at 3.328/3.332 eV. The doublet seems to originate from the columnar textured ZnO film structure. A corresponding structural dependence of the broadening parameter of the infrared dielectric functions was derived from spectroscopic ellipsometry in the spectral range from 380 to 1200 cm^− 1. The wave numbers of the E₁ transverse optical and A₁ longitudinal optical phonon modes of the ZnO films on silicon are determined to be 406 and 573 cm^− 1, respectively. These values are slightly smaller than those of single-crystalline ZnO thin films on sapphire.     

The influence of orientation on the photoluminescence behavior of ZnO thin films obtained by chemical solution deposition

A new type of ZnO thin films synthesized from chemical solution deposition at low temperature has been presented. X-ray powder diffraction and field emission scanning electron microscopy investigation reveal that the novel structured ZnO film is uniform and its [0001] direction is parallel to the substrate. The photoluminescence spectrum of this film shows strong ultraviolet band-gap emission and weak defect-related visible emission comparing to that of [0001]-oriented film, indicating high crystal quality of the non-[0001]-oriented ZnO film.