Effect of the oxygen pressure on the photoluminescence properties of ZnO thin films by PLD

ZnO thin films on Si(111) substrate were deposited by laser ablation of Zn target in oxygen reactive atmosphere; Nd-YAG laser with wavelength of 1064 nm was used as laser source. The experiments were performed at laser energy density of 31 J/cm², substrate temperature of 400 °C and various oxygen pressures (5–65 Pa). X-ray diffraction was applied to characterize the structure of the deposited ZnO films and the optical properties of the ZnO thin films were characterized by photoluminescence with an Ar ion laser as a light source using an excitation wavelength of 325 nm. The influence of the oxygen pressure on the structural and optical properties of ZnO thin films was investigated. It was found that ZnO film with random growth grains can be obtained under the condition of oxygen pressure 5–65 Pa. It will be clearly shown that the grain size and the formation of intrinsic defects depend on the oxygen partial pressure and that high optical quality of the ZnO films is obtained under low oxygen pressure (5 Pa, 11 Pa) conditions.     

Influence of oxygen partial pressure on the structure and photoluminescence of direct current reactive magnetron sputtering ZnO thin films

The effects of oxygen partial pressure on the structure and photoluminescence (PL) of ZnO films were studied. The films were prepared by direct current (DC) reactive magnetron sputtering with various oxygen concentrations at room temperature. With increasing oxygen ratio, the structure of films changes from zinc and zinc oxide phases, single-phase ZnO, to the (002) orientation, and the mechanical stresses exhibit from tensile stress to compressive stress. Films deposited at higher oxygen pressure show weaker emission intensities, which may result from the decrease of the oxygen vacancies and zinc interstitials in the film. This indicates that the emission in ZnO film originates from the oxygen vacancy and zinc interstitial-related defects. From optical transmittance spectra of ZnO films, the plasma edge shifts towards the shorter wavelength with the improvement of film stoichiometry.     

微孔状ZnO薄膜的生长与光致发光性

使用Zn（CH3COO）2·2H2O和PVA水溶液混合的办法在Si衬底上生长了微孔结构的ZnO薄膜。样品的晶体结构、形貌及光致发光性使用XRD、SEM及PL谱进行表征。结果表明所制备的ZnO为六方纤锌矿型晶体结构，微孔的孔壁是由纳米颗粒聚集而成，颗粒尺寸大约为20nm,关于这种结构的形成，我们推测PVA在微孔结构的形成过程中起到了模板作用。     

Effects of annealing temperature on the structure and photoluminescence properties of ZnO films

Zinc oxide (ZnO) films with c-orientation were deposited on Si (1 1 1) substrates at room temperature (RT) by RF-magnetron sputtering. Violet (394 and 412 nm) and green (560 and 588 nm) photoluminescence (PL) were observed from the as-deposited and annealed samples. The PL intensity was increasing with increasing annealing temperature (T_a). The 412 nm violet peak shifted from 412 to 407 nm and the 394 nm violet peak shifted from 394 to 399 nm on increasing the temperature from 500 to 900 °C, whereas no shift in PL green peaks was observed over the whole range of temperature examined. The 412 nm violet luminescence is ascribed to radiative defects related to the interface traps existing at grain boundaries. With the increase of T_a, the stress in the films changed from compressive to tensile, which is believed to have resulted in the observed 412 nm violet emission peak shifts from 412-407 nm. The 394 nm violet luminescence observed is attributed to free excitonic emission, and the increase of the crystal size may result in the 394 nm violet emission peak shifts from 394 to 399 nm. The other two PL bands located at 560 and 588 nm are attributed to oxygen deficiency.     

Annealing effect on the microstructure and photoluminescence of ZnO thin films

Zinc oxide thin films have been obtained by pulsed laser ablation of a ZnO target in O₂ ambient at a pressure of 0.13 Pa using a pulsed Nd:YAG laser. ZnO thin films deposited on Si (1 1 1) substrates were treated at annealing temperatures from 400 °C up to 800 °C after deposition. The structural and optical properties of deposited thin films have been characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, photoluminescence spectra, resistivity and IR absorption spectra. The results show that the obtained thin films possess good single crystalline with hexagonal structure at annealing temperature 600 °C. Two emission peaks have been observed in photoluminescence spectra. As the post-annealing temperature increase, the UV emission peaks at 368 nm is improved and the intensity of blue emission at 462 nm decreases, which corresponds to the increasing of the optical quality of ZnO film and the decreasing of Zn interstitial defect, respectively. The best optical quality for ZnO thin films emerge at post-annealing temperature 600 °C in our experiment. The measurement of resistivity also proves the decrease of defects of ZnO films. The IR absorption spectra of sample show the typical Zn–O bond bending vibration absorption at wavenumber 418 cm⁻¹.     

Study on the Hall-effect and photoluminescence of N-doped p-type ZnO thin films

N-doped, p-type ZnO thin films have been grown by plasma-assisted metal-organic chemical vapor deposition method. The results under optimized growth conditions included a resistivity of 1.72 Ω cm, a Hall mobility of 1.59 cm²/V s, and a hole concentration of 2.29 × 10¹⁸ cm^− 3, and were consistently reproducible. A N-related free-to-neutral-acceptor emission and an associated phonon replica were evident in room temperature photoluminescence spectra, from which the N acceptor energy level in ZnO was estimated to be 180 meV above the valence band maximum.     

Dependence of ferromagnetic properties on growth oxygen partial pressure in boron-doped ZnO thin films

Boron-doped ZnO films were prepared by pulsed laser deposition technique. Magnetic, electrical, and optical properties of Zn_1?x B _x O films have been studied. It is found that the magnetic properties of the Zn_1?x B _x O films are sensitive to growth oxygen partial pressure. The films deposited under a high oxygen partial pressure of about 10?Pa appear to be ferromagnetic insulators at room temperature (RT). However, when the oxygen partial pressure decreases to 1.2?Pa, the films are non-ferromagnetic conductors at RT. Zn vacancies, which can be controlled by the oxygen partial pressure, are shown to be essential for realizing ferromagnetism (FM); on the other hand, the n-type nature of ZnO has no contribution to the FM observed in the B-doped ZnO films.     

Optical and photoluminescence studies of gold nanoparticles embedded ZnO thin films

Gold nanoparticles (AuNPs) embedded ZnO thin films were prepared by sandwiching a thin thermally evaporated Au film between two sputtered ZnO films. The films were characterized by high resolution transmission electron microscopy (HRTEM), glancing angle X-ray diffraction (GXRD), optical absorption and photoluminescence (PL) measurements. GXRD data exhibited peaks which were attributed to the reflections from various ZnO and Au planes. Size dependence of the plasmon absorption was studied by forming nanoparticles with various sizes. Optical absorption spectra showed strong absorption due to localized surface plasmons at about 608, 638 and 676 nm for films having average AuNPs sizes of 27, 40 and 67 nm respectively. AuNPs embedded ZnO film showed a strong reduction in the intensity of photoluminescence, which was prominent in the case of pure ZnO film. The rise in temperature at a single nanoparticle site was calculated to be 22 K for a particle size of 80 nm.     

Effects of laser irradiation on the structure and optical properties of ZnO thin films

The effects of laser irradiation on the surface microstructure and optical properties of ZnO films deposited on glass substrates were investigated experimentally and compared with those of thermal annealing. X-ray diffraction (XRD) and atomic force microscopy (AFM) measurements showed that the irradiation treatment with an Ar⁺ laser of 514 nm for 5 min improves the crystalline quality of ZnO thin films through increasing the grain size and enhancing the c-axis orientation, with the effects similar to those of the thermal annealing at 500 °C for 1 h. Laser irradiation was found to be more effective both for the relaxation of the residual compressive stress in the as-grown films and for the modification of the surface morphology. A significant increase in the UV absorption and a widening in the optical band-gap of the films were also observed after laser irradiation.     

Correlation between film quality and photoluminescence in sputtered ZnO thin films

A red photoluminescence (PL) is observed in as-deposited ZnO thin films which are prepared by a conventional sputtering method. The PL intensity strongly depends on sputtering deposition conditions. In as-deposited and annealed films, it is found that there exists a correlation between the red PL intensity and the film quality. The origin of the red PL is attributed to the native defect induced during the sputtering deposition process. It is shown that the red PL measurement is effective as an evaluation method of the film quality.     

The effects of oxygen partial pressure on local structural properties for Ga-doped ZnO thin films

We report on Raman scattering studies of Ga-doped ZnO thin films that were grown by intentionally changing oxygen partial pressure in order to study the influences of oxygen partial pressure on local structural properties of this material. Raman spectra of ZnO:Ga (3 wt.% Ga-doped) films revealed vibrational modes at 575 and 630–660 cm^− 1 in addition to the host phonons of ZnO. These additional modes correspond to local vibrational modes associated with oxygen vacancy (V_O) and Ga impurity (Ga_Zn), respectively. With increasing oxygen partial pressure (oxygen flow rate up to ∼ 10 sccm), the 575-cm^− 1 mode decreases in its intensity, indicating the reduced V_O concentration. Further increasing oxygen partial pressure (> 10 sccm), we find a substantial disorder apparent in host ZnO phonons and some additional modes. These results suggest that the oxygen-rich condition may cause the formation of compensating-defects such as oxygen interstitials (O_i), Zn vacancy (V_Zn) and their complexes (Ga_Zn–O_i, Ga_Zn–V_Zn), strongly reducing carrier concentration in this system.     

Preparation of Li and Er codoped ZnO thin films and their photoluminescence

Li-Er codoped ZnO thin films have been prepared on Si(100) substrates by pulsed laser deposition (PLD). Both the as-grown and post-annealed films exhibit good crystalline quality with preferred c-axis orientation. After post-annealing at 850 °C, the photoluminescence (PL) related to intra-4f shell of Er³⁺ can be clearly observed. The Li-Er codoped ZnO film shows higher intensity of PL around 1.54 μm than the Er monodoped ZnO film. The behavior is attributed to the lowering of the symmetry of the crystal field around Er³⁺ ions by introducing Li⁺ into ZnO lattice, which is also confirmed by Raman scattering spectra.     

Enhanced photoluminescence from polycrystalline ZnO films resulting from oxygen processing

We report studies of photoluminescence from polycrystalline ZnO films deposited on sapphire as a function of the in situ oxygen pressure during growth and ex situ annealing. The ultraviolet photoluminescence was observed to increase by more than two orders of magnitude as a result of the annealing treatment. Enhanced cathodoluminescence was observed from the same films. The role of oxygen defects is discussed.     

磁控溅射制备ZnO:Eu薄膜发光性能研究

采用射频磁控溅射法在蓝宝石基片上制备ZnO:Eu薄膜,通过X射线衍射仪和荧光分光光度计等测试其晶体结构和发光特性,分析退火对薄膜晶体结构和发光特性的影响.结果表明,ZnO:Eu薄膜为C轴择优生长的多晶薄膜,实现ZnO基质中掺杂Eu3+;退火样品结晶质量较好,有助于ZnO:Eu薄膜中Eu3+的5D0-7F2的能级跃迁发光;高于ZnO带隙的高能激发(间接激发)和Eu3+的7F0-5L6和7F3-5D2能级间的低能共振激发(直接激发)都能观察到Eu3+的5D0-7F2能级跃迁的特征发光(618nm);间接激发时存在ZnO基质与Eu3之间发生能量传递.     

Effect of oxygen partial pressure on the structural and optical properties of sputter deposited ZnO nanocrystalline thin films

We report the influence of deposition parameters such as oxygen partial pressure and overall sputtering pressure on the structural and optical properties of the as-grown ZnO nanocrystalline thin films. The films were prepared by dc magnetron sputtering using Zn metal target under two different argon and oxygen ratios at various sputtering pressures. Microstructure of the films was investigated using X-ray diffraction and scanning electron microscopy. Optical properties of the films were examined using UV-Visible spectrophotometer. The results show that the films deposited at low oxygen partial pressure (10%) contain mixed phase (Zn and ZnO) and are randomly oriented while the films deposited at higher oxygen partial pressure (30%) are single phase (ZnO) and highly oriented along the c-axis. We found that the oxygen partial pressure and the sputtering pressure are complementary to each other. The optical band gap calculated from Tauc's relation and the particle size calculation were in agreement with each other.     

退火温度对ZnO:Al透明导电薄膜结构和性能的影响

采用溶胶-凝胶法(sol-gel)在普通载玻片上制备了ZnO∶Al薄膜,在200～600℃下退火.利用XRD、紫外-可见光-近红外分光光度计和电阻测试仪等分析方法研究了不同退火温度对薄膜结构和光电性能的影响.结果表明,退火温度在300℃以上,薄膜开始结晶,400℃以上,薄膜出现明显结晶,且沿(002)方向择优取向,随着退火温度升高,(002)峰的强度逐渐增强,晶粒尺寸逐渐增加;薄膜在可见光范围内的透过率均＞85%以上,退火温度高的薄膜在可见光范围内的透过率明显提高,光学带隙在3.32～3.54eV,且随着温度的升高而降低;薄膜的电阻率随退火温度的增高而有所降低,但是仍较高,在103俜cm量级.     

Pulsed laser deposition and photoluminescence measurements of ZnO thin films on flexible polyimide substrates

In order to assess the potential of zinc oxide (ZnO) in flexible electronics applications, we created continuous ZnO films on polymeric substrates for evaluation of structural and optical properties. Specifically, we have used pulsed laser deposition to deposit ZnO films with thickness of several microns on flexible free-standing polyimide substrates. A KrF excimer laser (248 nm) operated at fluences of 3.0-6.2 J/cm² was used. ZnO films were deposited at temperatures between room temperature and 300 °C under O₂ atmosphere at a pressure of 50 Pa. Good flexibility characterizes the obtained layers and X-ray diffraction measurements show that films present all reflections of hexagonal ZnO. We discuss luminescence measurements on the films in relation to the complex interface phenomena expected in our samples.     

衬底温度对N-Al共掺杂ZnO薄膜形貌及光致发光性能的影响

采用超声喷雾热解法在不同衬底温度条件下沉积了N-Al共掺杂ZnO薄膜,衬底为普通硅酸盐玻璃。利用X射线衍射仪、原子力显微镜和荧光光谱仪表征了样品的晶体结构、形貌及室温光致发光性能。结果表明,ZnO颗粒尺寸随着衬底温度的升高而逐渐增大;低温下沉积的样品发光光谱中缺陷发射光占主导,随着衬底温度的升高这些缺陷发射光强度逐渐减弱,当温度升高到450℃时只有紫外发射光。缺陷发射光强度的减弱意味着薄膜缺陷浓度减小、晶体趋于完整,同时反映出施主型缺陷浓度随衬底温度的升高而逐渐减小,这对减弱ZnO薄膜p型掺杂时Vo或Zni等施主缺陷的自补偿效应很有意义。     

Effects of thermal annealing in oxygen plasma for buffer layers on properties of ZnO thin films

ZnO thin films with ZnO buffer layers were grown by plasma-assisted molecular beam epitaxy (PA-MBE) on p-type Si(100) substrates. Before the growth of the ZnO thin films, the ZnO buffer layers were deposited on the Si substrates for 20 minutes and then annealed at the different substrate temperature ranging from 600 to 800 degrees C in oxygen plasma. The structural and optical properties of the ZnO thin films have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and room-temperature (RT) photoluminescence (PL). A narrower full width at half maximum (FWHM) of the XRD spectra for ZnO(002) and a larger grain are observed in the samples with the thermal annealed buffer layers in oxygen plasma, compared to those of the as-grown sample. The surface morphology of the samples is changed from rugged to flat surface. In the PL spectra, near-band edge emission (NBEE) at 3.2 eV (380 nm) and deep-level emission (DLE) around 1.77 to 2.75 eV (700 to 450 nm) are observed. By increasing the annealing temperatures up to 800 degrees C, the PL intensity of the NBEE peak is higher than that of the as-grown sample. These results imply that the structural and optical properties of ZnO thin films are improved by the annealing process.     

Effect of oxygen pressure on the structural and optical properties of ZnO thin films on Si (111) by PLD

ZnO thin films were grown on Si (111) substrates by pulsed laser deposition (PLD) at various oxygen pressures in order to investigate the structural and optical properties of the films. The optical properties of the films were studied by photoluminescence spectra using a 325 nm He-Cd laser. The structural and morphological properties of the films were investigated by XRD and AFM measurements, respectively. The results suggest that films grown at 20 Pa and 50 Pa have excellent UV emission and high-quality crystallinity. The research of PL spectra indicates that UV emission is due to excitonic combination, the green band is due to the replacing of Zn in the crystal lattice for O and the blue band is due to the O vacancies.