Effects of Annealing Temperature on Structural and Optical Properties of ZnO Thin Films

The effects of annealing temperature on the structural and optical properties of ZnO films grown on Si （100） substrates by sol-gel spin-coating are investigated. The structural and optical properties are characterized by x-ray diffraction, scanning electron microscopy and photoluminescence spectra. X-ray diffraction analysis shows the crystal quality of ZnO films becomes better after annealing at high temperature. The grain size increases with the temperature increasing. It is found that the tensile stress in the plane of ZnO films first increases and then decreases with the annealing temperature increasing, reaching the maximum value of 1.8 GPa at 700℃. PL spectra of ZnO films annealed at various temperatures consists of a near band edge emission around 380 nm and visible emissions due to the electronic defects, which are related to deep level emissions, such as oxide antisite （OZn）, interstitial oxygen （Oi）, interstitial zinc （Zni） and zinc vacancy （VZn^-）, which are generated during annealing process. The evolution of defects is analyzed by PL spectra based on the energy of the electronic transitions.     

Photoluminescence of ZnO and Mn-Doped ZnO Polycrystalline Films Prepared by Plasma Enhanced Chemical Vapour Deposition

ZnO and Mn-doped ZnO polycrystalline films are prepared by plasma enhanced chemical vapour deposition at low temperature （220℃）, and room-temperature photoluminescence of the films is systematically investigated. Analysis from x-ray diffraction reveals that a11 the prepared films exhibit the wurtzite structure of ZnO, and Mndoping does not induce the second phase in the films. X-ray photoelectron spectroscopy confirms the existence of Mn^2＋ ions in the films rather than metalic Mn or Mn^4＋ ions. The emission efficiency of the ZnO film is found to be dependent strongly on the post-treatment and to degrade with increasing temperature either in air or in nitrogen ambient. However, the enhancement of near band edge （NBE） emission is observed after hydrogenation in ammonia plasma, companied with more defect-related emission. Furthermore, the position of NBE shifts towards to high-energy legion with increasing Mn-doped concentration due to Mn incorporation into ZnO lattice.     

Annealing effect on structure and green emission of ZnO nanopowder by decomposing precursors

ZnO nanopowder is successfully synthesized by annealing the precursors in oxygen gas using the chemical precipitation method. Structural and optical properties of thus synthesized ZnO nanopowder are characterized by scanning electron microscopy (SEM) and photoluminescence (PL). The morphology of ZnO nanopowders evolves from nanorod to cobble as annealing temperature increases from 500 to 1000~\du, while spiral structures are observed in the samples annealed at 900 and 1000~\du. The PL spectra of ZnO nanopowder consist of largely green and yellow emission bands. The green emission from ZnO nanopowder depends strongly on the annealing temperature with a peak intensity at a temperature lower than 800~℃ while the yellow emission is associated with interstitial oxygen \rm O_\i.     

Photoluminescence study on Eu-implanted GaN

The photoluminescence (PL) properties of Eu-implanted GaN thin films are studied. The experimental results show that the PL intensity is seriously affected by ion implantation conditions. The PL efficiency increases exponentially with annealing temperature increasing up to a maximum temperature of 1050℃. Moreover, the PL intensity for the sample implanted along the channelling direction is nearly twice more than that observed from the sample implanted along the random direction. The thermal quenching of PL intensity from 10K to 300K for sample annealed at 1050℃ is only 42.7%.     

Effect of high-temperature annealing on AIN thin film grown by metalorganic chemical vapor deposition

The effect of high-temperature annealing on A1N thin film grown by metalorganic chemical vapor deposition was investigated using atomic force microscopy, Raman spectroscopy, and deep ultra-violet photoluminescence （PL） with the excitation wavelength as short as ~ 177 nm. Annealing experiments were carded out in either N2 or vacuum atmosphere with the annealing temperature ranging from 1200 ℃ to 1600 ℃. It is found that surface roughness reduced and compres- sive strain increased with the annealing temperature increasing in both annealing atmospheres. As to optical properties, a band-edge emission peak at 6.036 eV and a very broad emission band peaking at about 4.7 eV were observed in the photoluminescence spectrum of the as-grown sample. After annealing, the intensity of the band-edge emission peak varied with the annealing temperature and atmosphere. It is also found that a much stronger emission band ranging from 2.5 eV to 4.2 eV is superimposed on the original spectra by annealing in either N2 or vacuum atmosphere. We attribute these deep-level emission peaks to the VAL--ON complex in the A1N material.     

The effects of post-thermal annealing on the optical parameters of indium-doped ZnO thin films

Indium-doped ZnO thin films are deposited on quartz glass slides by RF magnetron sputtering at ambient temper- ature. The as-deposited films are annealed at different temperatures from 400 C to 800 C in air for 1 h. Transmittance spectra are used to determine the optical parameters and the thicknesses of the films before and after annealing using a nonlinear programming method, and the effects of the annealing temperatures on the optical parameters and the thickness are investigated. The optical band gap is determined from the absorption coefficient. The calculated results show that the film thickness and optical parameters both increase first and then decrease with increasing annealing temperature from 400 C to 800 C. The band gap of the as-deposited ZnO:In thin film is 3.28 eV, and it decreases to 3.17 eV after annealing at 400 C. Then the band gap increases from 3.17 eV to 3.23 eV with increasing annealing temperature from 400 C to 800 C.     

Luminescence Properties of Nanostructure ZnO-Covered Carbon Fibers Prepared by Thermal Oxidation

We report on ZnO nanosheets and nanorods synthesized by thermal oxidation of zinc films deposited on carbon fiber surfaces. The structure and optical properties are characterized by x-ray diffraction, scanning electron microscopy and photoluminescence spectrum. An orange-red emission around 683 nm is found in the PL spectrum when the sample prepaxs at 400℃ for four hours in air. With annealing temperature increasing from 400℃ to 500℃, the blue shift is observed.     

Optical spectroscopy study of damage evolution in 6H-SiC by H_2~+ implantation

Lattice defects induced by ion implantation into Si C have been widely investigated in the decades by various techniques. One of the non-destructive techniques suitable to study the lattice defects in Si C is the optical characterization. In this work, confocal Raman scattering spectroscopy and photoluminescence spectrum have been used to study the effects of 134-ke V H_2~+ implantation and thermal treatment in the microstructure of 6 H-Si C single crystal. The radiation-induced changes in the microstructure were assessed by integrating Raman-scattering peaks intensity and considering the asymmetry of Raman-scattering peaks. The integrated intensities of Raman scattering spectroscopy and photoluminescence spectrum decrease with increasing the fluence. The recovery of the optical intensities depends on the combination of the implantation temperature and the annealing temperature with the thermal treatment from 700℃ to 1100℃. The different characterizations of Raman scattering spectroscopy and photoluminescence spectrum are compared and discussed in this study.     

Ultraviolet Luminescence in Mg0.12Zn0.88O Alloy Films

We investigate the origin of ultraviolet （UV） emission from Mg0.12 Zn0.88 O alloy thin films with a wurtzite structure fabricated on c-plane Al2O3 substrates by plasma assisted molecular beam epitaxy. At room temperature, the absorption edge and UV emission band of the Mg0.12Zn0.88O film shift to high-energy side compared with ZnO films. Temperature dependence of the photoluminescence spectra shows that the UV emission is composed of free exciton and neutral donor bound exciton emissions. Two-step dissociation processes of the UV emission are observed with the increasing temperature. The thermal quenching mechanism is attributed to the dissociation of the free exciton from the neutral donor bound exciton in the low temperature region and the dissociation of free electron and hole from the free exciton in the high temperature region.     

Synthesis and Optical Properties of ZnO Nanostructures

ZnO nanostructures with different morphologies were fabricated by changing the partial oxygen pressure. The structures, morphologies and optical properties of ZnO nanostructures were investigated by x-ray diffraction, field emission scanning electron microscopy and photoluminescence (PL) spectra at room temperature. All the samples show preferred orientation along the c-axis. The oxygen partial pressure and the annealing atmosphere have important effect on the PL property of ZnO nanostructures. The high oxygen partial pressure during growth of samples and high-temperature annealing of the ZnO samples in oxygen can increase oxygen vacancies and can especially increase antisite oxygen (OZn) defects, which degraded the near band-edge emission. However, the annealing in 1-12 can significantly modify the NBE emission.     

Preparation of p-type ZnO:(Al, N) by a combination of sol--gel and ion-implantation techniques

We report the preparation of p-type ZnO thin films on (0001) sapphire substrates by a combination of sol--gel and ion-implantation techniques. The results of the Hall-effect measurements carried out at room temperature indicate that the N-implanted ZnO:Al films annealed at 600\du\ have converted to p-type conduction with a hole concentration of $1.6\times10¹⁸cm^-3, a hole mobility of 3.67cm²/V.s and a minimum resistivity of 4.80cm.\Omega$. Ion-beam induced damage recovery has been investigated by x-ray diffraction (XRD), photoluminescence (PL) and optical transmittance measurements. Results show that diffraction peaks and PL intensities are decreased by N ion implantation, but they nearly recover after annealing at 600\du. Our results demonstrate a promising approach to fabricate p-type ZnO at a low cost.     

退火温度对ZnO薄膜结构和发光特性的影响

采用反应射频磁控溅射法在 Si(100)基片上制备了高c轴择优取向的ZnO薄膜，研究了退火温度对ZnO薄膜的晶粒尺度、应力状态、成分和发光光谱的影响，探讨了ZnO薄膜的紫外发光光谱和可见发光光谱与薄膜的微观状态之间的关系.研究结果显示,在600—1000℃退火温度范围内，退火对薄膜的织构取向的影响较小，但薄膜的应力状态和成分有比较明显的变化.室温下光致发光光谱分析发现，薄膜的近紫外光谱特征与薄膜的晶粒尺度和缺陷状态之间存在着明显的对应关系；而近紫外光谱随退火温度升高所呈现的整体峰位红移是各激子峰相对比例变 关键词： ZnO薄膜 退火 光致发光 射频反应磁控溅射 可见光发射     

Ti离子注入和退火对ZnS薄膜结构和光学性质的影响

利用真空蒸发法在石英玻璃衬底上制备了ZnS薄膜,将能量80 keV,剂量1×10¹⁷ cm^-2的Ti离子注入到薄膜中,并将注入后的ZnS薄膜进行退火处理,退火温度500—700 ℃.利用X射线衍射（XRD）研究了薄膜结构的变化,利用光致发光（PL）和光吸收研究了薄膜光学性质的变化.XRD结果显示,衍射峰在500 ℃退火1 h后有一定程度的恢复;光吸收结果显示,离子注入后光吸收增强,随着退火温度的上升,光吸收逐渐降低,吸收边随着退火温度的提高发生蓝移;PL显示,薄 关键词： ZnS薄膜 离子注入 X射线衍射 光致发光     

Structural and optical properties of Au-implanted ZnO films

The structural and luminescence related optical behaviours of Au ion implanted ZnO films grown by magnetic sputtering and their post implantation annealing behaviours in the temperature range of 100-700 °C have been investigated. Optical absorption and transmittance spectra of the films indicate that band edge of Au-implanted ZnO has shifted to high energy range and optical band gap has increased, because the sharp difference of thermal expansion induces the lattice mismatch between ZnO and SiO₂. PL spectra reveal that UV and visible luminescence bands of ZnO films can be improved after thermal annealing due to recovery of defects and Au ions incorporation. Importantly, green luminescence band of 530 nm has been only observed in the Au-implanted and subsequently annealed ZnO films and it enhances with the increasing annealing temperature, which can be related to Au atoms or clusters in ZnO films. Furthermore, X-ray photoelectron spectroscopy measurements reveal that the Au⁰ is dominant state in Au implanted and annealed ZnO films. Possible mechanisms, such as optical transitions of Au atoms or clusters and deep level luminescence of ZnO, have been proposed for green emission.     

Effect of annealing temperature and annealing atmosphere on the structure and optical properties of ZnO thin films on sapphire (0 0 0 1) substrates by magnetron sputtering

ZnO thin films were epitaxially grown on sapphire (0 0 0 1) substrates by radio frequency magnetron sputtering. ZnO thin films were then annealed at different temperatures in air and in various atmospheres at 800 °C, respectively. The effect of the annealing temperature and annealing atmosphere on the structure and optical properties of ZnO thin films are investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), photoluminescence (PL). A strong (0 0 2) diffraction peak of all ZnO thin films shows a polycrystalline hexagonal wurtzite structure and high preferential c-axis orientation. XRD and AFM results reveal that the better structural quality, relatively smaller tensile stress, smooth, uniform of ZnO thin films were obtained when annealed at 800 °C in N₂. Room temperature PL spectrum can be divided into the UV emission and the Visible broad band emission. The UV emission can be attributed to the near band edge emission (NBE) and the Visible broad band emission can be ascribed to the deep level emissions (DLE). By analyzing our experimental results, we recommend that the deep-level emission correspond to oxygen vacancy (V_O) and interstitial oxygen (O_i). The biggest ratio of the PL intensity of UV emission to that of visible emission (I_NBE/I_DLE) is observed from ZnO thin films annealed at 800 °C in N₂. Therefore, we suggest that annealing temperature of 800 °C and annealing atmosphere of N₂ are the most suitable annealing conditions for obtaining high quality ZnO thin films with good luminescence performance.     

Luminescence mechanism of ZnO thin film investigated by XPS measurement

The effects of annealing environment on the luminescence characteristics of ZnO thin films that were deposited on SiO₂/Si substrates by reactive RF magnetron sputtering were investigated by X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL). An analysis of the O 1s peak of ZnO film revealed that the concentration of oxygen vacancies increased with the annealing temperature from 600 °C to 900 °C under an ambient atmosphere. The PL results demonstrated that the intensity of green light emission at 523 nm also increased with temperature. Under various annealing atmospheres, the analyses of PL indicated that only one emission peak (523 nm) was obtained, indicating that only one class of defect was responsible for the green luminescence. The green light emission was strongest and the concentration of oxygen vacancies was highest when the ZnO film was annealed in ambient atmosphere at 900 °C. The results in this investigation show that the luminescence mechanism of the emission of green light from a ZnO thin film is associated primarily with oxygen vacancies. PACS 81.15.Cd; 81.40.Ef; 78.55.-m; 78.55.Et     

氮气氛中高温退火对ZnO薄膜发光性质的影响

以二乙基锌和水汽分别作为锌源和氧源,用LP-MOCVD方法在p型Si(100)衬底上生长了单一取向的ZnO薄膜。对得到的样品在氮气气氛中进行高温热处理,退火温度分别为900,1000,1100℃。利用室温PL谱、XRD、AFM、XPS等方法对样品的性质进行了研究。研究表明:(1)随着退火温度的升高,样品的结晶性质也逐渐提高,从表面形貌观察到晶粒尺寸逐渐增大;(2)当退火温度从900℃升高至1000℃时,样品的光致发光谱中可见光波段的发光强度有所减弱,而紫外波段的发光强度明显增强;当退火温度升高至1100℃时,可见光波段的发光几乎完全被抑制,而紫外波段的发光强度急剧增强。分析认为,高温退火改善晶体结晶质量的同时调制了样品的Zn/O比,氮气气氛下的热处理使得样品内的氧原子逸出,来自受主缺陷OZn的可见发射随温度升高逐渐减弱,而当退火温度达到1000℃以上时样品成为富锌状态,此时与施主缺陷Zni有关的紫外发射急剧增强。     

高浓度Er/Yb共掺ZnO薄膜的结构及室温光致发光特性

采用射频磁控溅射方法制备了Er/Yb共掺ZnO薄膜,研究了退火处理对高浓度Er/Yb共掺ZnO薄膜的结构演化和光致发光(PL)特性的影响。X射线衍射分析结果表明:Er/Yb掺杂导致ZnO薄膜的晶粒细化及择优取向性消失,ZnO晶粒随退火温度的增加而逐渐长大。900℃退火时,出现Er3 、Yb3 偏析,退火温度高于1000℃时,薄膜与基体间发生了界面反应,1200℃时,ZnO完全转变为Zn2SiO4相。光致发光测量结果表明:高于900℃退火处理后,Er/Yb共掺ZnO薄膜在1540 nm附近具有明显的光致发光,发光强度在退火温度为1050℃时达到最大值;光致发光光谱呈现典型的晶体基质中Er3 离子发光光谱所具有的明锐多峰结构特征。此外,探讨了薄膜结构演化及其对光致发光光谱的影响。     

退火对ZnO:Al薄膜光致发光性能的影响

 采用溶胶-凝胶工艺在石英衬底上制备ZnO:Al（AZO）薄膜，通过不同温度的退火处理，研究了退火对AZO薄膜结构和光致发光特性的影响。XRD图谱表明：所制备的薄膜具有c轴高度择优取向，随着退火温度的升高，(002)峰的强度逐渐增强，同时(002)峰的半高宽逐渐减小,表明晶粒在不断增大。未退火样品的光致发光（PL）谱由361 nm附近的紫外带边发射峰和500 nm附近的深能级发射峰组成。样品经退火后，以500 nm为中心的绿带发射逐渐减弱，而带边发射强度有所增强,并且逐渐红移到366 nm附近，与吸收边移动的测试结果相吻合。对经过不同时间退火的样品分析表明，AZO薄膜的发光特性与退火时间也有很大关系，时间过短可见波段的发射较强，但时间过长会使晶粒发生团聚，导致紫外发射峰强度减弱。