Effects of sapphire substrate annealing on ZnO epitaxial films grown by MOCVD

The annealing effects of sapphire substrate on the quality of epitaxial ZnO films grown by metalorganic chemical vapor deposition (MOCVD) were studied. The atomic steps formed on (0 0 0 1) sapphire (α-Al₂O₃) substrate surface by annealing at high temperature was analyzed by atomic force microscopy (AFM). The annealing effects of sapphire substrate on the ZnO films were examined by X-ray diffraction (XRD), AFM and photoluminescence (PL) measurements. Experimental results indicate that the film quality is strongly affected by annealing treatment of the sapphire substrate surface. The optimum annealing temperature of sapphire substrates is given.     

Influence of annealing atmosphere on ZnO thin films grown by MOCVD

ZnO films were deposited on c-plane sapphire substrates by metal-organic chemical vapor deposition (MOCVD). Annealing treatments for as-deposited samples were performed in different atmosphere under various pressures in the same chamber just after growth. The effect of annealing atmosphere on the electrical, structural, and optical properties of the deposited films has been investigated by means of X-ray diffraction (XRD), atomic force microscope (AFM), Hall effect, and optical absorption measurements. The results indicated that the electrical and structural properties of the films were highly influenced by annealing atmosphere, which was more pronounced for the films annealed in oxygen ambient. The most significant improvements for structural and electrical properties were obtained for the film annealed in oxygen under the pressure of 60 Pa. Under the optimum annealing condition, the lowest resistivity of 0.28 Ω cm and the highest mobility of 19.6 cm² v⁻¹ s⁻¹ were obtained. Meanwhile, the absorbance spectra turned steeper and the optical band gap red shifted back to the single-crystal value.     

Effects of annealing on properties of ZnO thin films prepared by electrochemical deposition in chloride medium

The development of cost-effective and low-temperature synthesis techniques for the growth of high-quality zinc oxide thin films is paramount for fabrication of ZnO-based optoelectronic devices, especially ultraviolet (UV)-light-emitting diodes, lasers and detectors. We demonstrate that the properties, especially UV emission, observed at room temperature, of electrodeposited ZnO thin films from chloride medium (at 70 °C) on fluor-doped tin oxide (FTO) substrates is strongly influenced by the post-growth thermal annealing treatments. X-ray diffraction (XRD) measurements show that the films have preferably grown along (0 0 2) direction. Thermal annealing in the temperature range of 150-400 °C in air has been carried out for these ZnO thin films. The as-grown films contain chlorine which is partially removed after annealing at 400 °C. Morphological changes upon annealing are discussed in the light of compositional changes observed in the ZnO crystals that constitute the film. The optical quality of ZnO thin films was improved after post-deposition thermal treatment at 150 °C and 400 °C in our experiments due to the reducing of defects levels and of chlorine content. The transmission and absorption spectra become steeper and the optical bandgap red shifted to the single-crystal value. These findings demonstrate that electrodeposition have potential for the growth of high-quality ZnO thin films with reduced defects for device applications.     

Photoluminescence study of pure and Li-doped ZnO thin films grown by sol-gel technique

The effect of annealing atmosphere, temperature and aging on the photoluminescence of pure and Li-doped ZnO thin films has been investigated. Annealing the pure ZnO in N₂ and He above 800 °C results in green emission centered at ca. 500 nm; however annealing in air red-shifts the green emission to 527 nm. The visible emission of the Li-doped ZnO is found to be largely dependent on the annealing atmosphere. Warm-white photoluminescence with a broad emission band covering nearly the whole visible spectrum is obtained for the Li-doped ZnO films annealed in helium. The substitutional and interstitial extrinsic point defects created by lithium doping may mediate the relative concentration of the intrinsic defects and thereby tune the intrinsic-defect-related visible emission. The enhanced intensity ratio of near-band-edge ultraviolet emission to deep-level visible emission with aging time may be ascribed to both in-diffusion of oxygen from air and self-diffusion of oxygen interstitials to heal the oxygen vacancies during the aging process.     

Effect of annealing on the properties of N-doped ZnO films deposited by RF magnetron sputtering

N-doped ZnO films were deposited by RF magnetron sputtering in N₂/Ar gas mixture and were post-annealed at different temperatures (T_a) ranging from 400 to 800 °C in O₂ gas at atmospheric pressure. The as-deposited and post-annealed films were characterized by their structural (XRD), compositional (SIMS, XPS), optical (UV-vis-NIR spectrometry), electrical (Hall measurements), and optoelectronic properties (PL spectra). The XRD results authenticate the improvement of crystallinity following post-annealing. The weak intensity of the (0 0 2) reflection obtained for the as-deposited N-doped ZnO films was increased with the increasing T_a to become the preferred orientation at higher T_a (800 °C). The amount of N-concentration and the chemical states of N element in ZnO films were changed with the T_a, especially above 400 °C. The average visible transmittance (400-800 nm) of the as-deposited films (26%) was increased with the increasing T_a to reach a maximum of 75% at 600 °C but then decreased. In the PL spectra, A⁰X emission at 3.321 eV was observed for T_a = 400 °C besides the main D⁰X emission. The intensity of the A⁰X emission was decreased with the increasing T_a whereas D⁰X emission became sharper and more optical emission centers were observed when T_a is increased above 400 °C.     

Al掺杂原子分数及退火温度对ZnO薄膜光学特性的影响

 采用溶胶凝胶法在（0001）Al₂O₃衬底上制备了不同掺杂原子分数的ZnO:Al薄膜,在Ar气氛中进行了600～950 ℃不同温度的退火处理,研究了掺杂原子分数和退火温度对薄膜光致发光、光吸收和透射的影响。结果显示,薄膜的紫外峰强度随掺杂原子分数和退火温度的提高而增强,与缺陷相关的绿光强度却随着掺杂原子分数和退火温度的提高而降低;薄膜光学带隙随掺杂原子分数的提高从3.21 eV增大到3.25 eV;光吸收在可见光区随着退火温度的升高而增大,在紫外区却随着退火温度的升高而减小,透射与吸收的变化规律相反;薄膜吸收边随退火温度的升高出现轻微的红移。     

Al掺杂原子分数及退火温度对ZnO薄膜光学特性的影响

采用溶胶凝胶法在（0001）Al2O3衬底上制备了不同掺杂原子分数的ZnO:Al薄膜,在Ar气氛中进行了600～950 ℃不同温度的退火处理,研究了掺杂原子分数和退火温度对薄膜光致发光、光吸收和透射的影响。结果显示,薄膜的紫外峰强度随掺杂原子分数和退火温度的提高而增强,与缺陷相关的绿光强度却随着掺杂原子分数和退火温度的提高而降低;薄膜光学带隙随掺杂原子分数的提高从3.21 eV增大到3.25 eV;光吸收在可见光区随着退火温度的升高而增大,在紫外区却随着退火温度的升高而减小,透射与吸收的变化规律相反;薄膜吸收边随退火温度的升高出现轻微的红移。     

Investigation on the effect of Zr doping in ZnO thin films by spray pyrolysis

Zirconium doped zinc oxide thin films with enhanced optical transparency were prepared on Corning 1737 glass substrates at the substrate temperature of 400 °C by spray pyrolysis method for various doping concentrations of zirconium (IV) chloride in the spray solution. The X-ray diffraction studies reveal that the films exhibit hexagonal crystal structure with polycrystalline grains oriented along (0 0 2) direction. The crystalline quality of the films is found to be deteriorating with the increase of doping concentration and acquires amorphous state for higher concentration of 8 at.% in precursor solution. The average transmittance for 5 at.% (solution) zirconium doped ZnO film is significantly increased to ∼92% in the visible region of 500-800 nm. The room temperature photoluminescence (PL) spectra of films show a band edge between 3.41 and 3.2 eV and strong blue emission at 2.8 eV irrespective of doping concentration and however intensity increases consistently with doping levels. The vacuum annealing at 400 °C reduced the resistivity of the films significantly due to the coalescence of grains and the lowest resistivity of 2 × 10⁻³ Ω cm is observed for 3 at.% (solution) Zr doped ZnO films which envisages that it is a good candidate for stable TCO material.     

Effect of cobalt doping and annealing on properties of titania thin films prepared by sol-gel process

Undoped and cobalt doped titania (TiO₂) thin films have been prepared on Si(1 0 0) monocrystal and quartz substrate using the sol-gel deposition method and annealed in air at 450, 550, 650, 750, 850, 950 and 1050 °C. Several experimental techniques (AFM, XRD, Raman spectroscopy, XRR, EDX, XPS, XAS, UV-VIS spectroscopy) have been used to characterize these films. Further more the degree of light induced hydrophilicity was estimated by measuring the contact angle of a water droplet on the film. Increase of the annealing temperature and in smaller degree also cobalt doping predispose titania crystallite growth. The rutile phase was detected at lower temperatures in the cobalt doped films than in the undoped titania films. Cobalt in the cobalt doped TiO₂ was seen to be in Co²⁺ oxidation state, mainly in CoTiO₃ phase when films were annealed at temperatures higher than 650 °C. Cobalt compounds segregated into the sub-surface region and to the surface of the titania, where they formed islands. Cobalt doping red-shifted the fundamental absorption edge further into the visible range, however it did not enhance the light induced hydrophilicity of the thin film surface as compared to the undoped titania thin films.     

Role of vanadium content in ZnO thin films grown by pulsed laser deposition

Vanadium-doped ZnO films (Zn_1−xV_xO, where x = 0.02, 0.03, 0.05 and 0.07), were formed from ceramic targets on c-cut sapphire substrates using pulsed laser deposition at substrate temperature of 600 °C and oxygen pressure of 10 Pa. In order to clarify how the vanadium concentration influences the films’ properties, structural and magnetic investigations were performed. All films crystallised in wurtzite phase and presented a c-axis preferred orientation at low concentrations of vanadium. The results implied that the doping concentration and crystalline microstructure influence strongly the system's magnetic characteristics. Weak ferromagnetism was registered for the film with the lowest doping concentration (2 at.%), which exhibited a ferromagnetic behavior at Curie temperature higher than 300 K. Increasing the vanadium content in the film caused degradation of the magnetic ordering.     

退火对多晶ZnO薄膜结构与发光特性的影响

用射频反应溅射法在Si（111）衬底上制备了C轴取向的多晶ZnO薄膜，通过不同温度的退火处理，研究了退火对多晶ZnO薄膜结构和发光特性的影响.由x射线衍射得知，随退火温度的升高，晶粒逐渐变大，薄膜中压应力由大变小至出现张应力.光致发光测量发现，样品在430nm附近有一光致发光峰, 峰的强度随退火温度升高而减弱，联合样品电阻率随退火温度升高而逐渐变大的测量及能级图，推测出ZnO薄膜中的蓝光发射主要来源于锌填隙原子缺陷能级与价带顶能级间的跃迁. 关键词： ZnO薄膜 退火 光致发光 射频反应溅射     

退火氛围对掺杂ZnO薄膜磁性的影响

采用直流磁控反应共溅法制备了非磁性元素Al和磁性元素Co掺杂的ZnO薄膜, 样品原位真空退火后再空气退火处理. 利用X射线衍射仪(XRD) 和物理性能测量仪(PPMS) 对薄膜的结构和磁性进行了表征. XRD和PPMS结果表明, 不同的退火氛围对掺杂薄膜的结构和磁性有着很大的影响. 真空退火的Al掺杂ZnO薄膜没有观察到铁磁性, 而空气退火的样品却显示出明显的室温铁磁性, 铁磁性的来源与空气退火后导致Al和ZnO基体间电荷转移增强有关. 而对于Co掺杂ZnO薄膜, 真空退火后再空气退火, 室温铁磁性明显减弱. 其磁性变化与Co离子和ZnO基体间电荷转移导致磁性增强和间隙Co原子被氧化导致磁性减弱有关.     

Effects of temperature-induced stress on the structural,electrical, and optical properties of ZnO:Ga thin films grown on Si substrates

Crystalline ZnO:Ga thin films with highly preferential c-axis oriented crystals were prepared on Si(001) substrates at different temperatures using the reactive magnetron sputtering technique. Effects of temperature-induced stress in ZnO:Ga films were investigated using X-ray diffraction (XRD), atomic force microscopy (AFM), electrical transport, and spectroscopic ellipsometry measurements. XRD results showed that the films were highly c-axis (out-of-plane) oriented and crystallinity improved with growth temperature. The residual compressive stress in films grown at low temperature relaxes with substrate temperature and becomes tensile stress with further increases in growth temperature. Resistivity of the films decreases with increasing stress, while the carrier concentration and mobility increase as the stress increases. The mechanism of the stress-dependent bandgap of ZnO:Ga films grown at different temperatures is suggested in the present work.     

Influence of annealing temperature on structural and optical properties of ZnO: In thin films prepared by ultrasonic spray technique

Transparent conducting indium doped zinc oxide was deposited on glass substrate by ultrasonic spray method. The In doped ZnO samples with indium concentration of 3 wt.% were deposited at 300, 350 and 400 °C with 2 min of deposition time. The effects of substrate temperature and annealing temperature on the structural, electrical and optical properties were examined. The DRX analyses indicated that In doped ZnO films have polycrystalline nature and hexagonal wurtzite structure with (0 0 2) preferential orientation and the maximum average crystallite size of ZnO: In before and annealed at 500 °C were 45.78 and 55.47 nm at a substrate temperature of 350 °C. The crystallinity of the thin films increased by increasing the substrate temperature up 350 °C, the crystallinity improved after annealing temperature at 500 °C. The film annealed at 500 °C and deposited at 350 °C show lower absorption within the visible wavelength region. The band gap energy increased from E_g = 3.25 to 3.36 eV for without annealing and annealed films at 500 °C, respectively, indicating that the increase in the transition tail width. This is due to the increase in the electrical conductivity of the films after annealing temperature.     

Effects of high-temperature annealing on magnetic properties of V-doped GaN thin films grown by MOCVD

Metal organic chemical vapor deposition (MOCVD) has been used to grow vanadium-doped GaN (GaN:V) on c-sapphire substrate using VCl₄ as the V source. The as-grown GaN:V exhibited a saturated magnetic moment (M_s) of 0.28 emu/cm³ at room temperature. Upon high-temperature annealing treatment at 1100 °C for 7 min under N₂ ambient, the M_s of the GaN:V increased by 39.28% to 0.39 emu/cm³. We found that rapid thermal annealing leads to a remarkable increase in surface roughness of the V-doped GaN as well as the electron concentration. The annealing also leads to a significant increase in the Curie temperature (T_C), we have identified Curie temperatures about 350 K concluded from the difference between the field-cooled and zero-field-cooled magnetizations. Structure characterization by x-ray diffraction indicated that the ferromagnetic properties are not a result of secondary magnetic phases.     

The annealing effect on structural and optical properties of ZnO thin films produced by r.f. sputtering

In this work, a study of the structure and optical properties of undoped ZnO thin films produced by r.f. magnetron sputtering technique as a function of the growth parameters is reported. Modification under annealing conditions is also analysed. Raman spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction and optical transmittance have been used. From the position of the (002) X-ray diffraction peak and the E₂ (high) mode detected in Raman spectra, the residual stress both in the as-grown and in the annealed samples has been estimated.     

Effect of substrate and annealing on the structural and optical properties of ZnO:Al films

ZnO:Al thin films with c-axis preferred orientation were deposited on glass and Si substrates using RF magnetron sputtering technique. The effect of substrate on the structural and optical properties of ZnO:Al films were investigated. The results showed a strong blue peak from glass-substrate ZnO:Al film whose intensity became weak when deposited on Si substrate. However, the full width at half maxima (FWHM) of the Si-substrate ZnO:Al (0 0 2) peaks decreased evidently and the grain size increased. Finally, we discussed the influence of annealing temperature on the structural and optical properties of Si-substrate ZnO:Al films. After annealing, the crystal quality of Si-substrate ZnO:Al thin films was markedly improved and the intensity of blue peak (∼445 nm) increased noticeably. This observation may indicate that the visible emission properties of the ZnO:Al films are dependent more on the film crystallinity than on the film stoichiometry.     

退火温度对硼掺杂纳米金刚石薄膜微结构和p型导电性能的影响

采用热丝化学气相沉积法制备硼掺杂纳米金刚石 (BDND) 薄膜, 并对薄膜进行真空退火处理, 系统研究退火温度对BDND薄膜微结构和电学性能的影响. Hall效应测试结果表明掺B浓度为5000 ppm (NHB) 的样品的电阻率较掺B浓度为500 ppm (NLB) 的样品的低, 载流子浓度高, Hall迁移率下降. 1000 ℃退火后, NLB和NHB 样品的迁移率分别为53.3和39.3 cm²·V^-1·s^-1, 薄膜的迁移率较未退火样品提高, 电阻率降低. 高分辨透射电镜、紫外和可见光拉曼光谱测试结果表明, NLB样品的金刚石相含量较NHB样品高, 高的硼掺杂浓度使薄膜中的金刚石晶粒产生较大的晶格畸变. 经1000 ℃退火后, NLB和NHB薄膜中纳米金刚石相含量较未退火时增大, 说明薄膜中部分非晶碳转变为金刚石相, 为晶界上B扩散到纳米金刚石晶粒中提供了机会, 使得纳米金刚石晶粒中B浓度提高, 增强纳米金刚石晶粒的导电能力, 提高薄膜电学性能. 1000 ℃退火能够恢复纳米金刚石晶粒的晶格完整性, 减小由掺杂引起的内应力, 从而提高薄膜的电学性能. 可见光Raman光谱测试结果表明, 1000℃退火后, Raman谱图中反式聚乙炔 (TPA) 的1140 cm^-1峰消失, 此时薄膜电学性能较好, 说明TPA减少有利于提高薄膜的电学性能. 退火后金刚石相含量的增大、金刚石晶粒的完整性提高及TPA含量的大量减少有利于提高薄膜的电学性能. 关键词： 硼掺杂纳米金刚石薄膜 退火 微结构 电学性能     

Defects related room temperature ferromagnetism in p-type (Mn, Li) co-doped ZnO films deposited by reactive magnetron sputtering

We report on the defects related room temperature ferromagnetic characteristics of Zn_0.95-xMn_xLi_0.05O (x = 0.01, 0.03, 0.05 and 0.08) thin films grown on glass substrates using reactive magnetron sputtering. By increasing the Mn content, the films exhibited increases in the c-axis lattice constant, fundamental band gap energy, coercive field and remanent magnetization. Comparison of the structural and magnetic properties of the as-deposited and annealed films indicates that the hole carriers, together with defects concentrations, play an important role in the ferromagnetic origin of Mn and Li co-doped ZnO thin films. The ferromagnetism in films can be described by bound magnetic polaron models with respect to defect-bound carriers.     

Properties of ZnO thin films grown on Si substrates by photo-assisted MOCVD

ZnO thin films were grown on (1 0 0) p-Si substrates by Photo-assisted Metal Organic Chemical Vapor Deposition (PA-MOCVD) using diethylzinc (DEZn) and O₂ as source materials and tungsten-halogen lamp as a light source. The effects of tungsten-halogen lamp irradiation on the surface morphology, structural and optical properties of the deposited ZnO films have been investigated by means of atomic force microscope (AFM), X-ray diffraction and photoluminescence (PL) spectra measurements. Compared with the samples without irradiation, the several characteristics of ZnO films with irradiation are improved, including an improvement in the crystallinity of c-axis orientation, an increase in the grain size and an improvement in optical quality of ZnO films. These results indicated that light irradiation played an important role in the growth of ZnO films by PA-MOCVD.