Effect of substrate temperature on the structural and optical properties of ZnO and Al-doped ZnO thin films prepared by dc magnetron sputtering

ZnO and Al-doped ZnO(ZAO) thin films have been prepared on glass substrates by direct current (dc) magnetron sputtering from 99.99% pure Zn metallic and ZnO:3 wt%Al₂O₃ ceramic targets, the effects of substrate temperature on the crystallization behavior and optical properties of the films have been studied. It shows that the surface morphologies of ZAO films exhibit difference from that of ZnO films, while their preferential crystalline growth orientation revealed by X-ray diffraction remains always the (0 0 2). The optical transmittance and photoluminescence (PL) spectra of both ZnO and ZAO films are obviously influenced by the substrate temperature. All films exhibit a transmittance higher than 86% in the visible region, while the optical transmittance of ZAO films is slightly smaller than that of ZnO films. More significantly, Al-doping leads to a larger optical band gap (E_g) of the films. It is found from the PL measurement that near-band-edge (NBE) emission and deep-level (DL) emission are observed in pure ZnO thin films. However, when Al was doped into thin films, the DL emission of the thin films is depressed. As the substrate temperature increases, the peak of NBE emission has a blueshift to region of higher photon energy, which shows a trend similar to the E_g in optical transmittance measurement.     

Ag掺杂p型ZnO薄膜及其光电性能研究

采用超声喷雾热分解法在石英衬底上以醋酸锌水溶液为前驱体,以硝酸银水溶液为Ag掺杂源生长了Ag掺杂ZnO(ZnO：Ag)薄膜.研究了衬底温度对所得ZnO：Ag薄膜的晶体结构、电学和光学性质的影响规律.所得ZnO：Ag薄膜结构良好,在室温光致发光谱中检测到很强的近带边紫外发光峰,透射光谱中观测到非常陡峭的紫外吸收截止边和较高的可见光区透过率,表明薄膜具有较高的晶体质量与较好的光学特性.霍尔效应测试表明,在500℃下获得了p型导电的ZnO：Ag薄膜,载流子浓度为5.30×10¹⁵cm关键词： ZnO：Ag薄膜 p型掺杂 超声喷雾热分解 霍尔效应     

原位氧化Zn3N2制备p型ZnO薄膜的性能研究

采用射频反应溅射法在玻璃衬底上制备Zn₃N₂薄膜，然后向真空室中通入纯氧气进行热氧化制备ZnO薄膜.利用X射线衍射、扫描电子显微镜、霍尔效应测量、透射光谱和光致发光光谱等表征技术，研究了氧化温度和氧化时间对ZnO薄膜的结晶质量、电学性质和光学性能的影响.研究结果显示，450 ℃ 下氧化2 h后的样品中除含有ZnO外，还有Zn₃N₂成分，500 ℃下氧化2 h可以制备出电阻率为0.7 Ωcm，空穴载流子浓度为10^{关键词： p型ZnO薄膜 3N₂薄膜')" href="#">Zn₃N₂薄膜 射频溅射 原位氧化}     

Electrical and optical properties of Ga doped zinc oxide thin films deposited at room temperature by continuous composition spread

Ga doped ZnO (GZO) thin films were deposited on glass substrates at room temperature by continuous composition spread (CCS) method. CCS is thin films growth method of various Ga_xZn_1−xO(GZO) thin film compositions on a substrate, and evaluating critical properties as a function position, which is directly related to material composition. Various compositions of Ga doped ZnO deposited at room temperature were explored to find excellent electrical and optical properties. Optimized GZO thin films with a low resistivity of 1.46 × 10⁻³ Ω cm and an average transmittance above 90% in the 550 nm wavelength region were able to be formed at an Ar pressure of 2.66 Pa and a room temperature. Also, optimized composition of the GZO thin film which had the lowest resistivity and high transmittance was found at 0.8 wt.% Ga₂O₃ doped in ZnO.     

Structure distortion, optical and electrical properties of ZnO thin films co-doped with Al and Sb by so--gel spin coating

ZnO thin films co-doped with Al and Sb with different concentrations and a fixed molar ratio of AlCl₃ to SbCl₃ at 1:2, are prepared by a sol--gel spin-coating method on glass annealed at 550 ℃ for 2 h in air. The x-ray diffraction results confirm that the ZnO thin films co-doped with Al and Sb are of wurtzite hexagonal ZnO with a very small distortion, and the biaxial stresses are 1.03×10⁸, 3.26×10⁸, 5.23×10⁸, and 6.97×10⁸ Pa, corresponding to those of the ZnO thin films co-doped with Al and Sb in concentrations of 1.5, 3.0, 4.5, 6.0 at% respectively. The optical properties reveal that the ZnO thin films co-doped with Al and Sb have obviously enhanced transmittance in the visible region. The electrical properties show that ZnO thin film co-doped with Al and Sb in a concentration of 1.5 at% has a lowest resistivity of 2.5Ω·cm.     

Synthesis of cauliflower-like ZnO-TiO2 composite porous film and photoelectrical properties

A series of cauliflower-like TiO₂-ZnO composite porous films with various molar ratios of Zn/Ti were prepared by the screen printing technique on the fluorine-doped SnO₂ (FTO) conducting glasses. The composite films were characterized by field-emission scanning electron microscopy (FE-SEM), X-ray energy-dispersive spectrometry (EDS) and UV-vis transmittance spectrum. The results showed composite film electrode had a novel cauliflower-like morphology, which could effectively increase the dye absorption. The corresponding dye-sensitized solar cells (DSCs) were made by the composite film, and effects of ZnO incorporation on the photovoltaic performances of the DSCs were studied. With the Zn/Ti molar ratio not more than 3% in ZnO-TiO₂ composite film of about 5 μm-thickness, the photocurrent density (J_sc) and the solar-to-electricity conversion efficiency (η) were greatly improved compared with those of the DSC based on bare TiO₂ film of same thickness. This increases in efficiency and J_sc were attributed to high electron conductivity of ZnO, the improved dye adsorption and large light transmittance of composite film.     

Spectroscopic ellipsometry modeling of ZnO thin films with various O2 partial pressures

ZnO films were deposited on thermally oxidized SiO₂/p-type Si (100) substrates and glass substrates by DC magnetron sputtering using a metal Zn target. Three types of samples were prepared with various O₂/(Ar + O₂) ratios (O₂ partial pressure) of 20%, 50%, and 80%. The properties of these ZnO thin films were investigated using X-ray diffraction (XRD), optical transmittance, atomic force microscopy (AFM), and spectroscopic ellipsometry in the spectral region of 1.7–3.1 eV. The structural and optical properties of ZnO thin films were affected by O₂ partial pressure. Relationships between crystallinity, the ZnO surface roughness layer, and the refractive index (n) were investigated with varying O₂ partial pressure. It was shown that the spectroscopic ellipsometry extracted parameters well represented the ZnO thin film characteristics for different O₂ partial pressures.     

Room temperature transparent conducting oxides based on zinc oxide thin films

Doped zinc oxide thin films are grown on glass substrate at room temperature under oxygen atmosphere, using pulsed laser deposition (PLD). O₂ pressure below 1 Pa leads to conductive films. A careful characterization of the film stoichiometry and microstructure using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) concludes on a decrease in crystallinity with Al and Ga additions (≤3%). The progressive loss of the (0 0 2) orientation is associated with a variation of the c parameter value as a function of the film thickness and substrate nature. ZnO:Al and ZnO:Ga thin films show a high optical transmittance (>80%) with an increase in band gap from 3.27 eV (pure ZnO) to 3.88 eV and 3.61 eV for Al and Ga doping, respectively. Optical carrier concentration, optical mobility and optical resistivity are deduced from simulation of the optical data.     

Transitions of microstructure and photoluminescence properties of the Ge/ZnO multilayer films in certain annealing temperature region

The Ge/ZnO multilayer films have been prepared by rf magnetron sputtering. The effects of annealing on the microstructure and photoluminescence properties of the multilayers have been investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier-transform infrared (FTIR) spectrometry and photoluminescence (PL) spectrometry. The investigation of structural properties indicates that Zn₂GeO₄ has been formed with (2 2 0) texture and Zn deficiency from Ge/ZnO multilayer films in the process of annealing. However, lower Zn/Ge ratio can be improved by annealing. The annealed multilayers show three main emission bands at 532, 700, and 761 nm, which originate from the transition between oxygen vacancy () and Zn vacancies (V_Zn), the radiative recombination of quantum-confined excitons (QCE) in Ge nanocrystals, and the optical transition in the GeO color centers, respectively. Finally, the fabrication of thin film Zn₂GeO₄ from Ge/ZnO multilayer films by annealing at low temperature provides another approach to prepare the green-emitting oxide phosphor film:Zn₂GeO₄:Mn.     

掺银氧化锌纳米棒的水热法制备研究

利用水热法在直流磁控溅射制备的掺铝氧化锌 (AZO) 种子层上制备了不同形貌和光学性能的掺银ZnO纳米棒, 并采用XRD、扫描电镜、透射谱、光发射谱和EDS谱详细研究了Ag离子与Zn离子的摩尔百分比 (R_Ag/Zn) 及AZO种子层对掺银ZnO纳米棒的结构和光学性质的影响. 随着R_Ag/Zn的增加, 掺银ZnO 纳米棒的微结构和光学性质的变化与银掺杂诱导的纳米棒的端面尺寸变化有关. 平均端面尺寸的变化归结于种子层颗粒大小和颗粒数密度不同导致掺入的Ag离子的相对比例不同. 溅射15 min的AZO种子层上生长的ZnO纳米棒由于缺陷增多导致在可见光区的发光峰明显强于溅射10 min 的AZO种子层上、相同R_Ag/Zn 条件下生长的ZnO纳米棒. Ag掺杂产生的点缺陷增多导致可见光区PL波包较宽. 纯ZnO纳米棒的微结构与种子层厚度导致的结晶度和颗粒大小有关. 关键词： ZnO纳米棒 水热法 Ag掺杂 直流磁控溅射     

Deposition of ZnO multilayer on LiNbO3 single crystals by DC-magnetron sputtering

Zinc oxide (ZnO) thin films were deposited on LiNbO₃ (LN) single crystals with 200 nm thicknesses by three different ways, where coating of zinc (Zn) film was followed by thermal oxidation for four, two, and one steps with 50, 100, and 200 nm thicknesses repeatedly. Sample, which was produced at 4-step of deposition and oxidation of Zn layer, showed high transmittance and low structural defect due to a lower photoluminescence intensity and Urbach energy. Average grain size in X-ray diffraction (XRD), scanning electron microscopy (SEM) micrograph, and atomic force microscopy (AFM) images for multilayer of ZnO was lower than monolayer of ZnO thin films. Applying multilayer coating technique leads to decrease of surface roughness and scattering on light on surface and fabrication of LiNbO₃ waveguides with lower optical loss.     

The growth of ZnO:Ga:Cu as new TCO film of advanced electrical,optical and structural quality

Because of having similarities in many physical as well as chemical properties to those of Zn, Cu has been strategically used as an effective dopant e.g., Al, Ga, F, etc., to change the optical, electrical and the micro-structural properties of ZnO thin films for obtaining its favorable opto-electronic performance as a transparent conducting oxide suitable for devices. Present study demonstrates the growth of transparent conducting ZnO:Ga:Cu thin films, by low power RF magnetron sputtering at a low substrate temperature (100 °C). Highly crystalline ZnO:Ga:Cu film with preferred c-axis orientation has been obtained demonstrating a high magnitude of transmission ~85% in the visible range and a high electrical conductivity ~40 S cm^–1, facilitated by large crystallite size (~29 nm), introducing reduced grain boundary scattering. XPS O 1S spectrum reveals the presence of a significant fraction of oxygen atoms effectively increasing the optical transparency. Incorporation of Ga and Cu ions into the ZnO matrix promotes violation of the local translational symmetry as suggested by the relaxation of Raman selection rules for the network, evident by the presence of strong (B₁^high–B₁^low) modes which are typically Raman inactive. The consequences of Cu doping has been compared with identically prepared ZnO and ZnO:Ga films.     

Effects of H2 ambient annealing in fully 0 0 2-textured ZnO:Ga thin films grown on glass substrates using RF magnetron co-sputter deposition

Gallium doped zinc oxide (ZnO:Ga) thin films were grown on glass substrates using RF magnetron co-sputtering, followed by H₂ ambient annealing at 623 K to explore a possibility of steady and low-cost process for fabricating transparent electrodes. While it was observed that the ZnO:Ga thin films were densely packed c-axis oriented self-textured structures, in the as-deposited state, the films contained Ga₂O₃ and ZnGa₂O₄ which had adverse effect on the electrical properties. On the other hand, post-annealing in H₂ ambient improved the electrical properties significantly via reduction of Ga₂O₃ and ZnGa₂O₄ to release elemental Ga which subsequently acted as substitutional dopant increasing the carrier concentration by two orders of magnitude. Transmittance of the ZnO:Ga thin films were all over 90% that of glass while the optical band gap varied in accordance with the carrier concentrations due to changes in Fermi level. Experimental observation in this study suggests that transparent conductive oxide (TCO) films based on Ga doped ZnO with good electrical and optical properties can be realized via simple low-cost process.     

Effect of energetic electron beam treatment on Ga-doped ZnO thin films

Transparent conductive zinc oxide (ZnO) thin films were synthesized by a sol–gel spin coating method with the addition of Ga(NO₃)₃ in a Zn(CH₃COO)₂ solution and exposed to electron beam treatment. The UV–Vis spectra demonstrated that all of the films had transmittances of over 85% in the visible region. When Ga(NO₃)₃ was added to the ZnO precursor solution, the resistivity of the ZnO thin film decreased and the carrier concentration increased significantly. After electron beam treatment was performed on the 0.4 at.% Ga-doped ZnO film, the optical band gap increased and the resistivity significantly decreased resulting from the increases of the carrier concentration and mobility. By combining Ga doping and electron beam treatment, the resistivity of the ZnO thin film was reduced by a factor of nine hundred.     

Effect of excimer laser annealing on the properties of ZnO thin film prepared by sol-gel method

Pristine ZnO thin films have been deposited with zinc acetate [Zn(CH₃COO)₂], mono-ethanolamine (stabilizer), and isopropanol solutions by sol-gel method. After deposition, pristine ZnO thin films have been irradiated by excimer laser (λ = 248, KrF) source with energy density of 50 mJ/cm² for 30 sec. The effect of excimer laser annealing on the optical and structural properties of ZnO thin films are investigated by photoluminescence and field emission scanning electron microscope. As-grown ZnO thin films show a huge peak of visible region and a wide full width at half maximum (FWHM) of UV region due to low quality with amorphous ZnO thin films. After KrF excimer laser annealing, ZnO thin films show intense near-band-edge (NBE) emission and weak deep-level emission. The optically improved pristine ZnO thin films have demonstrated that excimer laser annealing is novel treatment process at room temperature.     

Hydrothermal growth of ZnO on annealed electrodeposited titanate film: Influence of zinc nitrate and methenamine

Hydrothermal growth of hexagonal ZnO nanorods on the annealed titanate nanotube films is reported as a function of molar ratio of Zn(NO₃)₂ and methenamine (1:1-1:4). The molar ratio of 1:4 results in a dense and thinner rod in comparison with other molar ratios. Corn-like structures of the rods are believed to be due to the higher amine concentration. Raman peaks at 437 and 331 cm⁻¹ are assigned to E₂ and E_2H-E_2L modes. Near band gap edge and green photoluminescence emission indicates the structural and oxygen vacancy. O 1s peak is found built-up of sub-peaks at 530.62, 531.8 and 532.84 eV corresponding to O²⁻ on normal wurtzite structure and OH and oxygen vacancies of ZnO, respectively.     

Effect of Mn doping on the nanostructure and optical properties of ZnO films synthesized by magnetron sputtering

We investigated the microstructure and optical properties of Zn_1−xMn_xO films synthesized by the magnetron sputtering technique. Structural analyses suggest that Mn occupied the Zn sites successfully and did not change the wurtzite structure of ZnO. In addition, nanoscale columnar grain arrays were found in the Mn-doped ZnO films. The experimental results indicate that moderate Mn doping could enhance the photoluminescence emission of ZnO. The possible origin of the emissions from our samples was also explored.     

Effects of the substrate and oxygen partial pressure on the microstructures and optical properties of Ti-doped ZnO thin films

Ti-doped ZnO (ZnO:Ti) thin films were deposited on the glass and Si substrates using radio frequency reactive magnetron sputtering. The effects of substrate on the microstructures and optical properties of ZnO:Ti thin films were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and a fluorescence spectrophotometer. The structural analyses of the films indicated that they were polycrystalline and had a hexagonal wurtzite structure on different substrates. When ZnO:Ti thin film was deposited on Si substrate, the film had a c-axis preferred orientation, while preferred orientation of ZnO:Ti thin film deposited on glass substrate changed towards (1 0 0). Finally, we discussed the influence of the oxygen partial pressures on the structural and optical properties of glass-substrate ZnO:Ti thin films. At a high ratio of O₂:Ar of 18:10 sccm, the intensity of (0 0 2) diffraction peak was stronger than that of (1 0 0) diffraction peak, which indicated that preferred orientation changed with the increase of O₂:Ar ratios. The average optical transmittance with over 93% in the visible range was obtained independent of the O₂:Ar ratio. The photoluminescence (PL) spectra measured at room temperature revealed four main emission peaks located at 428, 444, 476 and 527 nm. Intense blue-green luminescence was obtained from the sample deposited at a ratio of O₂:Ar of 14:10 sccm. The results showed that the oxygen partial pressures had an important influence for PL spectra and the origin of these emissions was discussed.     

Effects of hydrogen flow on properties of hydrogen doped ZnO thin films prepared by RF magnetron sputtering

The hydrogen doped ZnO (ZnO:H) thin films were deposited on quartz glass substrates by radio frequency magnetron sputtering. The doping characteristics of ZnO:H thin films with varied hydrogen flow ratio were investigated. At low hydrogen flow ratio (H₂/(H₂+Ar)≤0.02), the ZnO:H thin films exhibited dominant (002) peaks from X-ray diffraction and the lattice constants became smaller. The particles were mainly a columnar structure. The particles’ size became smaller, and the island-like structure appeared on the thin films surface. In addition, the low resistivity properties of ZnO:H thin films was ascribed to the increase of the carriers concentration and carriers mobility; When the hydrogen flow ratio was more than 0.02 (M≥0.02), two absorption bands at 1400–1800 cm^?1 and 3200–3900 cm^?1 were observed from the FT-IR spectra, which indicated that the ZnO:H thin films had typical Zn–H bonding, O–H bonding (hydroxyl), and Zn–H–O bonding (like-hydroxyl). The scanning electron microscope (SEM) results show that a large number of hydroxyl agglomeration formed an island-like structure on the thin films surface. The absorption peak at about 575 cm^?1 in the Raman spectra indicated that oxygen vacancies (V_O) defects were produced in the process of high hydrogen doping. In this condition, the low resistivity properties of ZnO:H thin films were mainly due to the increasing electron concentration resulted from V_O. Meanwhile, the Raman absorption peaks at approximately 98 cm^?1 and 436 cm^?1 became weaker, and the (002) XRD diffraction peak quenched and the lattice constants increased, which shows that the ZnO:H thin films no longer presented a typical ZnO hexagonal wurtzite structure. With the increasing of hydrogen flow ratio, the optical transmittance of ZnO:H thin films in the ultraviolet band show a clear Burstein–Moss shift effect, which further explained that electron concentration was increased due to the increasing V_O with high hydrogen doping concentration. Moreover, the optical reflectance of the thin films decreased, indicating the higher roughness of the films surface. It was noteworthy that etching effect of H plasma was obvious in the process of heavy hydrogen doping.     

Al-doped zinc oxide films grown by successive chemical solution deposition

Films of ZnO were grown and doped by the successive chemical solution deposition technique from a zincate solution containing aluminum (Al/Zn molar ratio in the range 2–10%). To our knowledge, this is the first report of its kind. A post-deposition heat treatment in argon (500 °C, 20 min) was performed for the activation of incorporated Al donors. Films were characterized by using scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, optical transmittance, photoluminescence and Hall-effect measurement. Films with a resistivity 0.2 Ω cm, carrier concentration 1.2×10¹⁸ cm^-3 and mobility 26 cm²/V s can be grown from a solution with Al/Zn = 10%. Further reduction in resistivity is plausible by using more heavily doped solutions and by the optimization of annealing parameters. Although the doping process does not change the films’ structure and surface morphology, it slightly lowers the optical transparency in the visible region and blue shifts the room-temperature photoluminescence peak to 378 nm. PACS  81.16.Be; 73.61.Ga; 78.55.Et; 79.60.-i; 68.55.Jk