Effect of preparation conditions on the microstructural characteristics and optical properties of oxidized zinc films

Thin films of zinc (Zn) were deposited onto glass substrates (maintained at room temperature) by thermal evaporation under vacuum. The metallic zinc films were submitted to thermal oxidation in air at 670 K and 770 K, respectively, for 5–90 min, in order to obtain zinc oxide (ZnO) thin films. X-ray diffraction patterns revealed that the ZnO thin films were polycrystalline and had a wurtzite (hexagonal) structure. The morphology of the prepared ZnO thin films was investigated using atomic force microscopy and scanning electron microscopy techniques. Transmission spectra were recorded in the spectral domain from 300 nm to 1400 nm. The optical energy bandgap calculated from the absorption spectra (supposing allowed direct transitions) was in the range 3.05–3.30 eV.     

Mn doped ZnO nanostructured thin films prepared by ultrasonic spray pyrolysis method

Mn-doped ZnO thin films with different percentage of Mn content (0, 1, 3 and 5 at.%) and substrate temperature of 350 °C, were deposited by a simple ultrasonic spray pyrolysis method under atmospheric pressure. We have studied the structural and optical properties by using X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) and ultra-violet visible near infrared (UV–Vis-NIR) spectroscopy. The lattice parameters calculated for the Mn-doped ZnO from XRD pattern were found to be slightly larger than those of the undoped ZnO, which indicate substitution of Mn in ZnO lattice. Compared with the Raman spectra for ZnO pure films, the Mn-doping effect on the spectra is revealed by the presence of additional peak around 524 cm⁻¹ due to Mn incorporation. With increasing Mn doping the optical band gap increases indicating the Burstein–Moss effect.     

Photoluminescence blue shift of indium phosphide nanowire networks with aluminum oxide coating

This paper describes our finding that optical properties of semiconductor nanowires were modified by depositing a thin layer of metal oxide. Indium phosphide nanowires were grown by metal organic chemical vapor deposition on silicon substrates with gold catalyst resulting in three‐dimensional nanowire networks, and optical properties were obtained from the collective nanowire networks. The networks were coated with an aluminum oxide thin film deposited by plasma‐enhanced atomic layer deposition. We studied the dependence of the peak wavelength of photoluminescence spectra on the thickness of the oxide coatings. A continuous blue shift in photoluminescence spectra was observed when the thickness of the oxide coating was increased. The observed blue shift is attributed to the Burstein–Moss effect due to increased carrier concentration in the nanowire cores caused by repulsion from intrinsic negative fixed charges located at the inner oxide surface. Samples were further characterized by scanning electron microscopy, Raman spectroscopy, transmission electron microscopy, and selective area diffractometry to better understand the physical mechanisms for the blue shift. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural,electrical and optical studies on spray-deposited aluminium-doped ZnO thin films

Thin films of zinc oxide (ZnO) were deposited on cleaned glass substrates by chemical spray pyrolysis technique using Zn(CH₃COO)₂ as precursor solution. Also, aluminium-doped thin films of ZnO were prepared by using AlCl₃ as doping solution for aluminium. The dopant concentration [Al/Zn atomic percentage (at%)] was varied from 0 to 1.5 at% in thin films of ZnO prepared in different depositions. Structural characterization of the deposited films was performed with X-ray diffraction (XRD) studies. It confirmed that all the films were of zinc oxide having polycrystalline nature and possessing typical hexagonal wurtzite structure with crystallite size varying between 100.7 and 268.6 nm. The films exhibited changes in relative intensities and crystallite size with changes in the doping concentration of Al. The electrical studies established that 1 at% of Al-doping was the optimum for enhancing electrical conduction in ZnO thin films and beyond that the distortion caused in the lattice lowered the conductivity. The films also exhibited distinct changes in their optical properties at different doping concentrations, including a blue shift and slight widening of bandgap with increasing Al dopant concentration.     

W掺杂ZnO透明导电薄膜的理论及实验研究

本文从理论与实验两方面入手, 对高价态差金属W掺杂ZnO (WZO) 薄膜材料的特性进行分析讨论. 采用基于密度泛函理论的平面波赝势方法对WZO材料特性进行理论分析, 计算结果表明: W以替位形式掺入ZnO六角纤锌矿晶格结构中, 由于W-O键的键长较长引起晶格常数增加, 产生晶格畸变; 掺杂后费米能级进入导带, 其附近的导电电子主要由W 5d, O 2p及Zn 3d电子轨道提供, 材料表现出n型半导体的特性; 同时能带简并效应使其光学带隙展宽. 为进一步验证该理论分析结果的适用性, 本文采用脉冲直流磁控溅射技术进行了本征ZnO及WZO薄膜的实验研究, 结果表明: W掺入未改变ZnO的生长方式, 但引起薄膜的晶格常数增加, 电阻率由本征ZnO的1.35× 10^-2 Ω·cm减小到1.55× 10^-3 Ω·cm, 光学带隙由3.27 eV展宽到3.48 eV. 制备的WZO薄膜在400-1100 nm的平均透过率大于83%. 实验结果对理论计算结果进行了验证, 表明WZO薄膜作为透明导电薄膜的应用潜力.     

A comparative ab initio study of the structural,mechanical, electronic and optical behaviors of ZnO:Ni thin films with nanometer scale

The electronic and optical properties of undoped and Ni–doped ZnO thin films with nanometer scale have been studied in the wurtzite phase, by first–principle approach. Density functional theory has been employed to calculate the fundamental properties of the films using full–potential linearized augmented plane–wave method. Ni doping was found to reduce the bandgap value of the material. Additionally, DOS effective mass of the electrons was evaluated. It was revealed that the effective mass of the electrons at the bottom of conduction band increased with Ni doping. Decrease of reflectance for thin films with nanometer scale in the UV–vis region was observed. The substitution by Ni decreased the intensity of the peaks, and a red shift was observed in the absorption peak. Moreover, the static dielectric constant, and static refractive index decreased with Ni content. Energy loss function of the modeled compounds was also evaluated. All calculated parameters were compared with the available experimental and other theoretical results.     

A wet chemical preparation of transparent conducting thin films of Al-doped ZnO nanoparticles

A wet chemical deposition method for preparing transparent conductive thin films on the base of Al-doped ZnO (AZO) nanoparticles has been demonstrated. AZO nanoparticles with a size of 7 nm have been synthesised by a simple precipitation method in refluxed conditions in ethanol using zinc acetate and Al-isopropylate. The presence of Al in ZnO was revealed by the EDX elemental analysis (1.8 at.%) and UV–Vis spectroscopy (a blue shift due to Burstein–Moss effect). The obtained colloid solution with the AZO nanoparticles was used for preparing by spin-coating thin films on glass substrates. The film demonstrated excellent homogeneity and transparency (T > 90%) in the visible spectrum after heating at 400 °C. Its resistivity turned to be excessively high (ρ = 2.6 Ω cm) that we ascribe to a poor charge percolation due to a high film porosity revealed by SEM observations. To improve the percolation via reducing the porosity, a sol–gel solution was deposited “layer-by-layer” in alternation with layers derived from the AZO colloid followed by heating. As it was shown by optical spectroscopy measurements, the density of thus prepared film was increased more than twice leading to a significant decrease in resistivity to 1.3 × 10⁻² Ω cm.     

Photoconduction spectroscopy of p-type GaSb films

Excess carrier lifetimes (77 K) have been measured as function of the absorbed flux density in undoped p-type gallium antimonide films (GaSb/GaAs) using steady state photoconductivity measurements with the illumination wavelength of 1.1 μm. Using the results from Hall effect measurements along with the relations describing the lifetimes of the excess minority carriers in the bulk of the films and at the surface, the theoretical values of the effective excess carrier lifetime in the materials were also calculated. Discrepancies between the experimental and theoretical results were described using a two-layer model, by considering the variation in the charge distribution within the layer due to the presence of surface states, as well as the band offset between the layer and the substrate. Theoretical modeling of the experimental result yields values of different parameters such as band bending at the surface, minimum value of Shockley–Read–Hall lifetime and maximum value of the surface recombination velocity.     

Synthesis and characterization of single- and co-doped SnO2 thin films for optoelectronic applications

Doped SnO₂ thin films have been prepared by sputtering from two different targets: antimony doped tin oxide (ATO) and antimony and zinc doped tin oxide (AZTO). In the case of ATO ceramic, the antimony amount only reaches 0.012 mol per formula unit due to its evaporation at high temperature while the presence of Zn²⁺ in AZTO prevents the antimony evaporation, greatly enhances the ceramic density and allows the deposition of thin films with a high deposition rate. Both types of thin films have a dense morphology with a smooth surface and they are polycrystalline. For post-annealed ATO thin films, the Drude model was applied to deduce the carrier concentration, the optical mobility as well as the resistivity. The carrier concentration is around ten times higher for ATO thin films compared to AZTO. The two combined effects (higher carrier concentration and mobility) for ATO thin films doped with 1.2% of Sb lead to the best optoelectronic performances, confirming previous results obtained with ceramics. Nevertheless, we have a better opportunity to modulate the conductivity in the case of AZTO thin films.     

Effects of aluminum doping and substrate temperature on zinc oxide thin films grown by pulsed laser deposition

Aluminum-doped zinc oxide (AZO) thin films have been deposited on amorphous fused silica substrates by pulsed laser ablation of a Zn:Al metallic targets. We varied the film growth condition such as the substrate temperature and Al concentrations. The films were deposited at substrate temperatures ranging from 20 to 600°C with oxygen partial pressure of 1 torr. The characteristics of the deposited films were examined by analyzing their photoluminescence (PL), X-ray diffraction (XRD), and UV–visible spectra. It is observed that the optical bandgap energy of the deposited films increased with the increase of Al concentration and substrate temperature. Besides, the PL peak energy shifted to blue and the Stokes shift became larger as the Al content increased.     

Structural and electrical properties of fluorine-doped zinc tin oxide thin films prepared by radio-frequency magnetron sputtering

Transparent and conductive thin films of fluorine doped zinc tin oxide (FZTO) were deposited on glass substrates by radio-frequency (RF) magnetron sputtering using a 30 wt% ZnO with 70 wt% SnO₂ ceramic targets. The F-doping was carried out by introducing a mixed gas of pure Ar, CF₄, and O₂ forming gas into the sputtering chamber while sputtering ZTO target. The effect of annealing temperature on the structural, electrical and optical performances of FZTO thin films has been studied. FZTO thin film annealed at 600 °C shows the decrease in resistivity 5.47 × 10⁻³ Ω cm, carrier concentration ∼10¹⁹ cm⁻³, mobility ∼20 cm² V⁻¹ s⁻¹ and an increase in optical band gap from 3.41 to 3.60 eV with increasing the annealing temperatures which is well explained by Burstein–Moss effect. The optical transmittance of FZTO films was higher than 80% in all specimens. Work function (ϕ) of the FZTO films increase from 3.80 eV to 4.10 eV through annealing and are largely dependent on the amounts of incorporated F. FZTO is a possible potential transparent conducting oxide (TCO) alternative for application in optoelectronics.     

Effect of solution concentrations on crystal structure,surface topographies and photoluminescence properties of ZnO thin films

Zinc oxide thin films were deposited on silicon substrates via hydrothermal method. Microstructures, surface topographies and optical properties of ZnO thin films were systematically investigated by X-ray diffraction, atomic force microscopy and fluorescence spectrophotometer. The mean grain size and surface roughness of the thin films decrease first and then increase with increasing the concentration of zinc nitrate hexahydrate. The photoluminescence spectra of ZnO thin films, excited by the 240, 320, 360, 380 and 400 nm excitation wavelength, were investigated in detail. Based on our analysis, it can be noted that mechanisms of the ultraviolet, violet and blue emissions are attributed to the transitions from the localized levels below the conduction band, zinc vacancy, interstitial zinc and extended interstitial zinc levels to the valance band, respectively. Blue–violet emissions of ZnO have great potential in light emitting and biological fluorescence labeling applications.     

Crossover of polaron conductivity and the inhomogeneous state of lanthanum manganites in the magnetic phase transition region

The transport properties of lanthanum manganites over a wide range of temperatures below the magnetic phase transition point are discussed within the model of a two-phase composite whose phases differ in the magnetic order and charge carrier concentration. The volume ratio of the phases depends on the temperature and the magnetic field. The magnetoelastic polarons are charge carriers in both phases, and the metal-dielectric transition occurs as a percolation transition accompanied by the crossover of the polaron conductivity. The results obtained by numerical simulation of the resistivity, magnetoresistance, and thermopower are compared with the experimental data for La_0.7Mn_1.3O_3?δ thin films. The theoretical and experimental data are in good agreement.     

二维氧化锌纳米阵列的制备及光学吸收特性研究

采用漂移法,在玻璃衬底上制备出粒径分别为117,350和500 nm单层、大面积的聚苯乙烯胶体球掩膜板,在已制得的掩膜板上用射频磁控溅射的方法沉积一层氧化锌薄膜,最后用有机溶液四氢呋喃(THF)浸泡去除聚苯乙烯胶体球,获得不同粒径的二维氧化锌纳米团簇。通过扫描电子显微镜和能量色散X射线光谱仪对样品的形貌及成份进行表征,表明所制得样品为有序分布的蜂窝网状氧化锌纳米阵列。在室温下,通过吸收光谱仪测试样品在300～800 nm波长范围内的吸收光谱,结果表明对于具有不同尺寸晶粒的氧化锌纳米团簇样品,随着所采用的聚苯乙烯胶体球粒径的增大,即氧化锌纳米团簇粒径的增加,光吸收峰出现了宽化和红移;随着溅射时间的延长,即氧化锌薄膜膜厚的增加,光吸收率提高。此外,对氧化锌纳米团簇阵列的光吸收特性进行了基于离散偶极子近似的理论计算从而获得任意形状和尺寸粒子的吸收。目前,文献报道中用此理论计算各种形状的纳米金、银等金属的结果与实验结果相符,但是应用离散偶极子的近似理论计算氧化锌纳米颗粒的报道很少。应用此理论计算三角棱台形状的氧化锌光学吸收特性,根据氧化锌薄膜介电常数和膜厚的变化进行光吸收特性的模拟,并解释了实验结果。     

Absorption edge shift in ZnO thin films at high carrier densities

The optical absorption edge has been measured as a function of carrier concentration for thin films of zinc oxide prepared by organometallic chemical vapour deposition and reactive R.F. magnetron sputtering. Large shifts of the absorption edge have been observed which are only a function of the carrier concentration. Below n = 3 × 10¹⁹ cm^-3 the shifts are well described by the Burstein-Moss model. For carrier concentrations between 3–5 ×10¹⁹cm^-3, the shift decreases very rapidly, finally increasing again with further increases in the carrier density. These effects are consistent with a merging of the donor band with the conduction band following a semiconductor-metal transition.     

Assessing the antimicrobial activity of zinc oxide thin films using disk diffusion and biofilm reactor

The electronic and chemical properties of semiconductor materials may be useful in preventing growth of microorganisms. In this article, in vitro methods for assessing microbial growth on semiconductor materials will be presented. The structural and biological properties of silicon wafers coated with zinc oxide thin films were evaluated using atomic force microscopy, X-ray photoelectron spectroscopy, and MTT viability assay. The antimicrobial properties of zinc oxide thin films were established using disk diffusion and CDC Biofilm Reactor studies. Our results suggest that zinc oxide and other semiconductor materials may play a leading role in providing antimicrobial functionality to the next-generation medical devices.     

Cesium doped and undoped ZnO nanocrystalline thin films: a comparative study of structural and micro‐Raman investigation of optical phonons

Undoped and cesium‐doped zinc oxide (ZnO) thin films have been deposited on sapphire substrate (0001) using the sol–gel method. Films were preheated at 300 °C for 10 min and annealed at 600 and 800 °C for 1 h. The grown thin films were confirmed to be of wurtzite structure using X‐ray diffraction. Surface morphology of the films was analyzed using scanning electron microscopy. The photoluminescence (PL) spectra of ZnO showed a strong ultraviolet (UV) emission band located at 3.263 eV and a very weak visible emission associated with deep‐level defects. Cesium incorporation induced a blue shift of the optical band gap and quenching of the near‐band‐edge PL for nanocrystalline thin film at room temperatures because of the band‐filling effect of free carriers. A shift of about 10–15 cm⁻¹ is observed for the first‐order longitudinal‐optical (LO) phonon Raman peak of the nanocrystals when compared to the LO phonon peak of bulk ZnO. The UV resonant Raman excitation at RT shows multiphonon LO modes up to fifth order. Copyright © 2010 John Wiley & Sons, Ltd.     

Nickel/nickel oxide coatings for fiber batteries

A Nickel–Cadmium fiber micro–battery design consisting of a nickel/nickel oxide coated glass capillary tube, cadmium micro–wire, and polyimide micro–tube was evaluated in this paper. The nickel/nickel oxide thin films were deposited via electrolysis and the quality was evaluated via the effect of the sulfate concentration, plating temperature, plating solution pH, and heat treatment. The maximum voltage range of the fiber batteries ranged from 0.68–1.2 V, while the maximum current supplied by battery ranged from 0.6–1.0 mA. The results of this work demonstrate the feasibility of fiber batteries that can be readily adapted to random or ordered hole fibers and readily integrated into all-fiber optoelectronic devices.     

Investigation of chemical mechanical polishing of zinc oxide thin films

Zinc oxide has become an important material for various applications. Commercially available zinc oxide single crystals and as-grown zinc oxide thin films have high surface roughness which has detrimental effects on the growth of subsequent layers and device performance. A chemical mechanical polishing (CMP) process was developed for the polishing of zinc oxide polycrystalline thin films. Highly smooth surfaces with RMS roughness <6 Å (as compared to the initial roughness of 26 ± 6 Å) were obtained under optimized conditions with removal rates as high as 670 Å/min. Effects of various CMP parameters on removal rate and surface roughness were evaluated. The role of pH on the polishing characteristics was investigated in detail.     

半导体氮化铟(InN)的电学性质

本文总结了近年来半导体InN薄膜材料(主要是六方纤锌矿结构的InN及异质结构)的电学性质研究进展,重点内容为InN的载流子浓度和迁移率,造成InN中高电子浓度现象的施主分析、载流子输运特性及表面、界面特性等。同时也涉及了部分立方闪锌矿结构InN的电学特性和InN在器件(主要是高电子迁移率晶体管器件)上的潜在应用。