Epitaxial Aluminum-Doped Zinc Oxide Thin Films on Sapphire: I, Effect of Substrate Orientation

Epitaxial thin films of Al-doped zinc oxide have been grown on sapphire substrates by pulsed laser ablation. The effect of substrate temperature, background pressure of oxygen, and substrate orientation (A, M, R, C) on the orientation relationships between ZnO and sapphire have been evaluated using on- and off-axis X-ray diffractometry. Under all growth conditions zinc oxide, on A- and C-plane sapphire, grew with the c -axis perpendicular to the substrate. In contrast, on M and R orientations of sapphire, ZnO grew with its c -axis parallel or perpendicular to the substrate depending on the substrate temperature and background pressure employed during growth. In all cases only one unique in-plane relationship between the sapphire substrate and the zinc oxide film was found with the exception of the M-plane at high substrate temperatures.     

Crystallographic Orientation in Pure and Aluminum-Doped Zinc Oxide Thin Films Prepared by Sol–Gel Technique

Novel sol–gel processes for the preparation of grain-oriented thin films of pure and aluminum-doped zinc oxide (AZO) are reported. Using various stabilizing ligands, oxide films with different degree of c -axis orientation could be prepared on amorphous substrates. The origin of orientation in sol–gel-derived ZnO and AZO films is investigated. The texture selection of ZnO films is independent of the heat-treatment schedule but sensitive to the precursor system. The electrical properties of the films do not depend significantly on the crystallographic orientation. The film visible transmittance remained higher than 90% even after vacuum annealing.     

Preparation of Aluminum-Doped Zinc Oxide Films by a Normal-Pressure CVD Method

Aluminum-doped zinc oxide films prepared using a normal-pressure CVD (NP-CVD) method were studied as a transparent electrode material. The films were prepared on fused quartz substrates at 500°C using bis(2,4-pentanedionato)zinc and tris(2,4-pentanedionato)aluminum as source material. The transparent films, ∼0.3 μm in thickness, with a transmittance above 80% at a wavelength between 400 and 820 nm, were easily obtained. The optical band gap of the films increased from 3.3 to 3.6 eV with increasing amounts of aluminum dopant. The minimum resistivity of the film was about 4.9 × 10⁻⁵Ω·m.     

制备过程对掺铝氧化锌薄膜性质的影响

文章采用溶胶-凝胶法在玻璃基底上制备得到了高透光率,高导电性的掺铝氧化锌薄膜（AZO）,利用原子力显微镜、扫描电镜、X射多次退火的制备过程不仅可以得到可见光区透光率大于85%,电阻率为7.2×10-5Ω·m的透明导电薄膜,而且因省略了热处理过程而简化了制备工艺,缩短了制膜时间。线衍射仪和紫外可见分光光度计等研究了三种不同的制备过程对AZO性质的影响。结果表明,制备过程的不同导致了薄膜的表面形貌、结构和导电性质方面的差别,其中分层多次退火过程有利于晶粒长大,形成结晶度高且具有单一（002）取向的AZO薄膜,同时改善薄膜的导电性能。分层     

Effect of Microstructural Control on Thermoelectric Properties of Hot-Pressed Aluminum-Doped Zinc Oxide

The thermal conductivity of polycrystalline Al-doped ZnO was controlled through the fabrication of nanostructured polycrystalline materials, by hot-pressing nanosized Zn_{1– x} Al _x O ( x = 0.01, 0.02) particles, which were synthesized by a coprecipitation and spray-drying method. This process resulted in an improved thermoelectric power factor because of the nanosized Zn_0.99Al_0.01O particles of the polycrystalline products. The thermal conductivity also was decreased as a result of the formation of nanocrystalline Zn_0.99Al_0.01O.     

Electrical Properties of Gallium-Doped Zinc Oxide Films Prepared by RF Sputtering

Ga-doped polycrystalline ZnO films on glass substrates were prepared by sputtering the targets, which had been prepared by sintering disks consisting of ZnO powder and various amounts of Ga₂O₃, to investigate the effects of gallium doping and sputtering conditions on electrical properties. Optimizing the RF power density, argon gas pressure, and gallium content, transparent Ga-doped ZnO films with resistivity less than 10⁻³Ω·cm were obtained. Electron concentrations for undoped and Ga-doped ZnO films were on the order of 10¹⁸ and 10²¹/cm³, respectively. The Ga-doped ZnO films became degenerate when the electron concentration exceeded ∼ 10¹⁹/cm³, and the optical band gap increased with increasing carrier concentration because of the increase of Fermi energy in the conduction band.     

Sol-Gel Preparation of Transparent and Conductive Aluminum-Doped Zinc Oxide Films with Highly Preferential Crystal Orientation

Transparent aluminum-doped zinc oxide (ZnO) films were prepared via the sol-gel method on silica-glass substrates from 2-methoxyethanol solutions of zinc acetate and aluminum chloride that contained monoethanolamine. Dip coating was conducted at room temperature, with substrate withdrawal rates of 1.2-7.0 cm/min. After each deposition, the films were heat-treated in air at 200°-450°C for 10 min (pre-heat-treatment). After six to fourteen layers had been deposited, the films were then subjected to annealing in air at 500°-800°C for 1 h (the first post-heat-treatment), followed by annealing in nitrogen at 500°-700°C for 15 min to 4 h (the second post-heat-treatment). All the films obtained were transparent and showed only an extremely sharp ZnO (002) peak in the X-ray diffractometry (XRD) patterns. The effects of the aluminum content, the substrate withdrawal speed, and the heat-treatment conditions on the electrical resistivity of the films were studied. All these factors strongly affected the resistivity. The lowest resistivity value (6.5 10^-3 Omegacm) was achieved in a film that contained 0.5 at.% aluminum, prepared with a low substrate withdrawal speed (1.2 cm/min), and a pre-heat-treatment of individual layer at 400°C in air and a post-heat-treatment of the entire film at 600°C in air, followed by a post-heat-treatment at 600°C in nitrogen. These preparation parameters also affected the degree of crystal orientation, which was revealed by the intensity of the ZnO (002) XRD peak. Higher crystal orientation was effective in reducing the film resistivity, whereas the higher grain-packing density and possible aluminum segregation were thought to have positive and negative effects, respectively, in reducing the resistivity.     

Electrical Conductivity and Lattice Defects in Nanocrystalline Cerium Oxide Thin Films

The results of the electrical conductivity and Raman scattering measurements of CeO₂ thin films obtained by a polymeric precursor spin-coating technique are presented. The electrical conductivity has been studied as a function of temperature and oxygen activity and correlated with the grain size. When compared with microcrystalline samples, nanocrystalline materials show enhanced electronic conductivity. The transition from extrinsic to intrinsic type of conductivity has been observed as the grain size decreases to <100 nm, which appears to be related to a decrease in the enthalpy of oxygen vacancy formation in CeO₂. Raman spectroscopy has been used to analyze the crystalline quality as a function of grain size. A direct comparison has been made between the defect concentration calculated from coherence length and nonstoichiometry determined from electrical measurements.     

Defect Chemistry and Electrical Properties of Thallium Oxide Single Crystals

Ehdectrical resistivity and Hall voltage were measured between 4.2 and 300 K on T1₂O₃ crystals annealehd at 550°C for 24 h under oxygen pressures of 2×10⁴ to 10⁷ Pa. The carrier concentration varied from 7.97×10²⁰ to 5.08×10²⁰ cm⁻³, the low-temperature Hall mobility from 131 to 189 cm²/V.s, and the Fermi level from 7.1×10⁴ to 5.05×10⁴ J/mol above the bottom of the conduction band as P ₀₂ was increased from 2×10⁴ to 10⁷ Pa. The dependence of Fermi level on carrier concentration and P _0l was consistent with a parabolic density-of-states function describing the conduction band. Over the entire region of oxygen pressure investigated, Fermi-Dirac statistics were required to describe the dependence of carrier concentration on P ₀₂.     

Effects of Individual Layer Thickness on the Microstructure and Optoelectronic Properties of Sol–Gel-Derived Zinc Oxide Thin Films

Zinc oxide (ZnO) thin films were prepared under different conditions on glass substrates using a sol–gel process. The microstructure of ZnO films was investigated by means of diffraction analysis, and plan-view and cross-sectional scanning electron microscopy. It was found that the preparation conditions strongly affected the structure and the optoelectronic properties of the films. A structural evolution in morphology from spherical to columnar growth was observed. The crystallinity of the films was improved and columnar film growth became more dominant as the zinc concentration and the substrate withdrawal speed decreased. The individual layer thickness for layer-by-layer homoepitaxy growth that resulted in columnar grains was <20 nm. The grain columns are grown through the entire film with a nearly unchanged lateral dimension through the full film thickness. The columnar ZnO grains are c -axis oriented perpendicular to the interface and possess a polycrystalline structure. Optical transmittance up to 90% in the visible range and electrical resistivity as low as 6.8 × 10⁻³·Ω·cm were obtained under optimal deposition conditions.     

Impact of Hydrogen Passivation on Electrical Properties of Polysilicon Thin Films

Silicon - The effect of hydrogen passivation and heat treatments on the electronic activity at grain boundaries in thin films of polysilicon deposited by LP-CVD (Low Pressure Chemical Vapor...     

Structural,Electrical and Optical Properties of PVC/ZnTe Nanocomposite Thin Films

Journal of Inorganic and Organometallic Polymers and Materials - ZnTe nanoparticles (NPs) were synthesized using hydrothermal method and then were dispersed in poly(vinyl-chloride) (PVC) to prepare...     

Effect of Zn, Sr, and Y Addition on Electrical Properties of PZT Thin Films

We have investigated methods to increase the efficiency of piezoelectric micromachined ultrasonic transducers (pMUTs). pMUTs are driven by a thin piezoelectric layer on a Si membrane. The efficiency of pMUTs can be increased using a film with better ferroelectric properties. We have used Zn, Sr, and Y doping on PZT-based thin films along the morphotropic phase boundary (MPB) composition to increase their piezoelectric properties. The results obtained were then extended to compositions on both sides of the MPB. The sol–gel method was used to prepare precursor solutions, which were then spin coated on a Pt(100)/Ti/SiO₂/Si substrate to prepare the PZT thin films. It was found that Zn and Sr together had the most significant effect on the ferroelectric properties in which a saturation polarization of 108 μC/cm² and remanent polarization of 54 μC/cm² were achieved.     

Electrical Properties and Defect Structure of Zirconia: II, Tetragonal Phase and Inversion

The defect structure of tetragonal zirconia was investigated by measuring the temperature and oxygen partial pressure dependence of the electrical conductivity and the electronic transference number. Tetragonal zirconia was a mixed electronic and ionic conductor under all conditions studied. The n -type electronic conductivity observed at high temperatures and low oxygen partial pressures was interpreted on the basis of a defect model involving fully ionized oxygen vacancies. The conductivity change associated with the monoclinic ⇒ tetragonal phase transformation was isothermal, but the rate of change was a function of the thermal history and the method of preparation of the sample.     

磷掺杂对非晶硅薄膜结构及光电性能的影响

采用射频等离子增强化学气相沉积方法制备了磷掺杂氢化非晶硅(a-Si∶H)薄膜.通过Raman散射光谱研究了不同磷烷掺杂含量薄膜的微结构,利用分光光度计对薄膜的厚度、消光系数和折射率进行了模拟,用高阻仪测得了非晶硅薄膜暗电导率.结果表明:薄膜的中程有序度随着磷掺杂量φ(体积分数)的增加而减小;折射率在φ为0.8%时最大;...     

Effect of Copper Additive on the Microstructure and Electrical Properties of Polycrystalline Zinc Oxide

Nonohmic behavior is obtained for polycrystalline ZnO with copper as the only additive in the range 0.3 x 1 wt%. The effect of copper on the microstructure and electrical behavior of ZnO:Cu ceramics is investigated. The leakage current decreases and the breakdown electric field increases as the copper concentration increases. The large apparent dielectric constant of ZnO:Cu ceramic ( k > > k _ZnO, k _ZnO is the dielectric constant of pure ZnO) is attributed to the grain boundary barrier layer effect. A Schottky barrier height of 0.27–0.46 eV is obtained for various copper-added samples, depending on sintering temperatures.     

Influences of Cr Doping on the Electrical Properties in BiFeO3 Thin Films

Cr-doped BiFeO₃ (BFO) thin films were deposited on Pt(200)/TiO₂/SiO₂/Si(100) substrates by a chemical solution deposition method. The dielectric constant and dissipation factor of the BFO thin films decrease from 165 and 0.054 (undoped) to 100 and 0.02 (3 mol% Cr-doped) at a frequency of 10 kHz as the Cr content increases. The leakage current and ferroelectric properties were improved significantly by means of Cr doping. The leakage current density of 4.1×10^-6 A/cm² for the 3 mol% Cr-doped BFO thin film is about four orders of magnitude lower than that of undoped BFO thin film at an external electric field of 100 kV/cm. The 3 mol% Cr-doped BFO thin film exhibited a well-saturated hysteresis loop with a large remanent polarization (P_r) of 61 μC/cm² at room temperature. The reason for the improved leakage current and ferroelectric properties in Cr-doped BFO thin films can be attributed to the reduced oxygen vacancies in the films by Cr doping.

Communicated by Dr. George W. Taylor     

薄膜中ZnO/Ag的相对厚度对电学性能的影响

银作为低辐射镀膜玻璃的功能层,保证了低辐射镀膜玻璃具有优异的热力学性能.截至目前,银在低辐射镀膜玻璃中仍然起着不可替代的作用.而银层生长质量的好坏则决定了低辐射镀膜玻璃产品性能的好坏.通过对膜层结构中ZnO/Ag的相对厚度对电学性能的研究,当同时满足ZnO的厚度为4nm,Ag的厚度为10nm时,膜层的电学性质最为优异.