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.     

Effects of sapphire substrates surface treatment on the ZnO thin films grown by magnetron sputtering

The surface treatment effects of sapphire substrate on the ZnO thin films grown by magnetron sputtering were studied. The sapphire substrates properties have been investigated by means of atomic force microscopy (AFM) and X-ray diffraction rocking curves (XRCs). The results show that sapphire substrate surfaces have the best quality by CMP with subsequent chemical etching. The surface treatment effects of sapphire substrate on the ZnO thin films were examined by X-ray diffraction (XRD) and photoluminescence (PL) measurements. Results show that the intensity of (0 0 2) diffraction peak of ZnO thin films on sapphire substrates treated by CMP with subsequent chemical etching was strongest, FWHM of (0 0 2) diffraction peak is the narrowest and the intensity of UV peak of PL spectrum is strongest, indicating surface treatment on sapphire substrate preparation may improve ZnO thin films crystal quality and photoluminescent property.     

退火对ZnO薄膜光学特性的影响

用射频磁控溅射法在蓝宝石衬底上制备出ZnO薄膜,通过X射线衍射(XRD)、扫描电镜(SEM)和光致发光(PL)谱等研究了退火温度对ZnO薄膜结构和光学性质的影响。测量结果显示,所制备的ZnO薄膜为六角纤锌矿结构,具有沿c轴的择优取向;随着退火温度的升高,(002)XRD峰强度和平均晶粒尺寸增大,(002)XRD峰半高宽(FWHM)减小,光致发光紫外峰强度增强。结果证明,用射频磁控溅射法通过适当控制退火温度可得到高质量ZnO薄膜。     

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.     

Au层退火温度对ZnO/Au/ZnO多层膜的结构、光学及电学性质的影响

采用金属有机化学气相沉积(MOCVD)技术在蓝宝石衬底上制备出晶体质量较好的透明导电的ZnO/Au/ZnO(ZAZ)多层膜,其中,Au夹层是通过射频磁控溅射的方法获得。通过对Au夹层进行不同温度的退火处理,研究了Au层退火温度对ZAZ多层膜的结构特性、电学性能和光学特性的影响。利用原子力显微镜(AFM)、扫描电子显微镜(SEM)、X射线衍射(XRD)仪、霍尔效应测试和透射谱分析等测试手段对ZAZ多层膜的性质进行了分析。测试结果表明,在200 ℃下对Au夹层进行快速退火处理,多层膜的结构、电学和光学性质达到最优,表面等离子体效应也更明显。其中,XRD(002)衍射峰的半高宽为0.14°,电阻率为2.7×10^-3 Ω·cm,载流子浓度为1.07×10²⁰ cm^-3,可见光区平均透过率为75.3%。     

Effect of ZnO sacrificial layer thickness on the structure and optical properties of GaN nanoparticles prepared by RF magnetron sputtering

GaN nanoparticles were prepared on sapphire (0001) substrates with ZnO sacrificial layers by self assembly of Ga₂O₃ films in their reaction with NH₃. ZnO sacrificial layers with different thicknesses and Ga₂O₃ films were deposited on sapphire substrates in turn by a radio frequency (RF) magnetron sputtering system. Nitridation of the Ga₂O₃ films was then carried out in a quartz tube furnace. The effect of ZnO sacrificial layer thickness on the structure and optical properties of nanoparticles prepared by RF magnetron sputtering were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and photoluminescence (PL). GaN nanoparticles with ZnO sacrificial layers of different thicknesses possess hexagonal wurtzite crystal structure and have a preferred orientation with c axis perpendicular to the sapphire substrates. XRD, SEM, and AFM results reveal that the better-crystallinity, uniform, and well-dispersed GaN nanoparticles (～30 nm) without agglomeration were obtained with a ZnO sacrificial layer 300-nm thick. The PL result reveals that the optical properties of the GaN nanoparticles are improved with a ZnO sacrificial layer 300-nm thick. Therefore, we suggest that a ZnO sacrificial layer 300-nm thick is the most suitable condition for obtaining better-quality GaN nanoparticles with good luminescence performance. Moreover, the mechanism of the formation of GaN nanoparticles with ZnO sacrificial layers is also discussed.     

蓝宝石基片的处理方法对ZnO薄膜生长行为的影响

采用反应射频磁控溅射方法,在经过不同方法处理的蓝宝石基片上,在同一条件下沉积了ZnO薄膜.利用原子力显微镜、X射线衍射、反射式高能电子衍射等分析技术,对基片和薄膜的结构、表面形貌进行了系统表征.研究结果显示,不同退火条件下的蓝宝石基片表面结构之间没有本质的差异,均为α-Al₂O₃ (001)晶面,但基片表面形貌的变化较大.在不同方法处理的蓝宝石基片上生长的ZnO薄膜均具有高c轴取向的织构特征,但薄膜的表面形貌差异较大.基片经真空退火处 关键词： ZnO薄膜 反应磁控溅射 基片处理 形貌分析     

Optical properties of highly C-oriented Bi3TiNbO9 thin films grown on fused silica substrates by PLD

Highly aluminium-doped zinc oxide (ZnO) films have been grown on differently oriented sapphire substrates by magnetron sputtering from an oxidic target. Rocking curve measurements, Rutherford backscattering analysis and transmission electron microscopy show that the films exhibit a disturbed film growth. However, despite the large nominal lattice mismatch between ZnO and sapphire (-31%), the films grow epitaxially on every sapphire orientation, even at room temperature. This was proven by pole figure analysis. The reason that epitaxial growth can be observed is an incommensurate lattice fitting between ZnO and sapphire by a mutual rotational alignment of their lattices. Films of the best crystallographic quality have been grown on (110)-oriented sapphire, which is also reflected by the highest Hall mobility in these layers. PACS 68.55.ln; 73.50.Gr; 81.05.Dz; 81.15.Cd     

Epitaxial ZnO films grown on ZnO-buffered c-plane sapphire substrates by hydrothermal method

ZnO films are hydrothermally grown on ZnO-buffered c-plane sapphire substrates at a low temperature of 70 °C. A radio-frequency (RF) reactive magnetron sputtering has been used to grow the ZnO buffer layers. X-ray diffraction, scanning electron microscopy, and room temperature photoluminescence are carried out to characterize the structure, morphology and optical property of the films. It is found that the films are stress-free. The epitaxial relationship between the ZnO film and the c-plane sapphire substrate is found to be ZnO (0 0 0 1)||Al₂O₃ (0 0 0 1) in the surface normal and in plane. Sapphire treatment, as such acid etching, nitridation, and oxidation are found to influence the nucleation of the film growth, and the buffer layers determine the crystalline quality of the ZnO films. The maximum PL quantum efficiency of ZnO films grown with hydrothermal method is found to be about 80% of single-crystal ZnO.     

蓝宝石基片上制备大面积Tl2Ba2CaCu2O8超导薄膜

在2英寸双面蓝宝石基片上采用CeO₂作为缓冲层制备了高质量Tl₂Ba₂CaCu₂O₈(Tl-2212)超导薄膜.以金属铈作为溅射靶材,采用射频磁控反应溅射法生长了c轴织构的CeO₂缓冲薄膜,并研究了不同生长条件对于CeO₂缓冲层的晶体结构及表面形貌的影响.超导薄膜采用直流磁控溅射和后热处理的方法制备.扫描电子显微镜(SEM)图像显示,超     

Effects of crystalline quality on the ultraviolet emission and electrical properties of the ZnO films deposited by magnetron sputtering

The ZnO films were deposited on c-plane sapphire, Si (0 0 1) and MgAl₂O₄ (1 1 1) substrates in pure Ar ambient at different substrate temperatures ranging from 400 to 750 °C by radio frequency magnetron sputtering. X-ray diffraction, photoluminescence and Hall measurements were used to evaluate the growth temperature and the substrate effects on the properties of ZnO films. The results show that the crystalline quality of the ZnO films improves with increasing the temperature up to 600 °C, the crystallinity of the films is degraded as the growth temperature increasing further, and the ZnO film with the best crystalline quality is obtained on sapphire at 600 °C. The intensity of the photoluminescence and the electrical properties strongly depend on the crystalline quality of the ZnO films. The ZnO films with the better crystallinity have the stronger ultraviolet emission, the higher mobility and the lower residual carrier concentration. The effects of crystallinity on light emission and electrical properties, and the possible origin of the n-type conductivity of the undoped ZnO films are also discussed.     

Growth of epitaxial c ‐plane ZnO film on a ‐plane sapphire by radio frequency reactive magnetron sputtering

In this Letter, we report the successful growth of high quality c ‐plane oriented epitaxial ZnO films on a ‐plane sapphire substrates by using radio frequency reactive magnetron sputtering. The effect of substrate temperature on the structural and optical properties has been investigated. X‐ray diffraction (XRD) studies reveal that the ZnO film is grown epitaxially on a ‐plane sapphire substrate, and the film quality is improv‐ ed as the substrate temperature is increased. Photoluminescence (PL) results manifest that screw dislocations can exert great influence on the optical properties. It is found that the line width of the near‐band‐edge emission of PL decreases linearly with increase in screw density. In addition, a simple and effective method is proposed to assess the defect density in epitaxial ZnO films by performing PL measurement. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The microstructures and the electrical and optical properties of ZnO:N films prepared by thermal oxidation of Zn3N2 precursor

Samples of p-type ZnO:N films were prepared on glass substrates by thermal oxidation of Zn₃N₂ precursor, which was produced by reactive magnetron sputtering with a metallic zinc target in Ar/N₂ working gas. The microstructures and the electrical and optical properties of the samples were systematically investigated as a function of the annealing temperature. The results indicate that the annealing temperature has strong effects on the conductivity and photoluminescence (PL) properties of the obtained ZnO:N films. With an annealing temperature of 500 ^°C in oxygen flux, ZnO:N samples show the best p-type characteristics. The doping mechanism and the doping efficiency are briefly discussed based on the experimental results.     

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 post-annealing conditions on properties of ZnO:Ag films

Silver-doped ZnO films were grown on glass substrates by RF reactive magnetron sputtering. The as-grown ZnO:Ag film is insulating but behaves as p-type conduction with a resistivity of 152 Ω cm, a carrier concentration of 2.24×10¹⁶ cm^?3 and a Hall mobility of 1.83 cm²/V s after annealing in O₂ atmosphere at 600 ^°C for 1 h. The influence of post-annealing temperature and ambience on the electrical, structural and optical properties of the films was investigated.     

Microstructure and optical properties of ZnO/porous silicon nanocomposite films

In this study, porous silicon (PS) templates were formed by electrochemical anodization on p-type (100) silicon wafer and ZnO films were deposited on PS substrates using radio frequency (RF) reactive magnetron sputtering technique. The effects of oxygen partial pressures of growth ZnO films and annealing ambience on the microstructure and photoluminescence (PL) of the ZnO/PS nanocomposite films were systematically investigated by X-ray diffraction and fluorescence spectrophotometry. The results indicated that all ZnO/PS nanocomposite films were polycrystalline in nature with a hexagonal wurtzite structure and the (002) oriented ZnO films had the best crystal quality under O₂:Ar ratio of 10:10 sccm and annealing in vacuum. PL measurements at room temperature revealed that ZnO/PS nanocomposite systems formed a broad PL band including the blue and green emissions from ZnO and red-orange emission from the PS. The mechanism and interpretation of broadband PL of the nanocomposites were discussed in detail using an oxygen-bonding model in PS and a native defects model in ZnO.     

Photoluminescence of ZnO films prepared by r.f. sputtering on different substrates

Polycrystalline ZnO films with good orientation were deposited on sapphire, quartz, Si and 7059 glass substrates by r.f. magnetron sputtering. A strong UV photoluminescence (PL) peak (located at 356 nm) and a weak blue emission peak (located at 446 nm) were observed at room temperature (RT) for the films deposited on sapphire, quartz and Si substrates when excited with 270 nm light. For the films prepared on Corning 7059 glass, only a strong 446 nm blue emission peak was found, and the PL intensity decreased with increasing oxygen pressure during films deposition. The intensity of the UV emission increased 7 and 14 times, respectively, for the films on sapphire and quartz substrates after high temperature annealing in vacuum. The UV emission originates from the inter-band transition of electrons and the blue emission is due to transition of electrons from the shallow donor level of the oxygen vacancies to the valence band.     

不同衬底上的ZnO薄膜紫外光致发光

用射频磁控溅射法在蓝宝石、硅和石英衬底上沉积出具有好的择优取向的多晶ZnO薄膜. 在270 nm波长的光激发下室温下可观察到显著的紫外光发射（波长为356 nm）和较弱的蓝光发射（波长为446 nm）. 经高温退火后薄膜的结晶质量显著提高, 在蓝宝石、石英衬底上沉积的薄膜，其积分发光强度分别增加了7倍和14倍.而硅衬底上的膜发光强度增强不太显著.紫外光发射源于电子的带间跃迁，而蓝光发射是由电子从氧空位浅施主能级到价带顶的跃迁引起的. 关键词： ZnO薄膜 射频磁控溅射 紫外发光 退火     

Characteristics of ZnO epilayer on the post-annealed buffer layer on GaN/sapphire substrate by pulsed laser deposition

We employed epi-GaN substrates for ZnO film growth, and studied the deposition and post-annealing effects. ZnO films were grown by pulsed laser deposition (PLD) method. The as-grown films were annealed for one hour under atmospheric pressure air. ZnO morphologies after annealing were investigated and the post-annealed ZnO films grown at T _g =700^oC have very smooth surfaces and the rms with roughness is about 0.5 nm. Finally, ZnO post-annealed buffer layer was inserted between ZnO epilayer and GaN/sapphire substrates. It is confirmed by AFM that growth temperature of 700^oC helps the films grow in step-flow growth mode. It is observed by cathode luminescence spectrum that the ZnO film grown at 700^oC has very low visible luminescence, indicating the decrease of the deep level defects. It is also revealed by Hall measurements that carrier concentration is decreased by increasing the growth temperatures. It is suggested that low temperature buffer layer growth and post-annealing technique can be used to fabricate ZnO hetero-epitaxy.     

Effect of substrate annealing on the quality of pulsed laser deposited Zn1−xMgxO thin films

The annealing effects of sapphire substrate before deposition on the quality of epitaxial Zn_1−xMg_xO thin films grown by pulsed laser deposition are reported. Our Experimental results indicate that the surface quality of Zn_1−xMg_xO thin films and hexagonal columnar growth is improved on the annealed sapphire substrate at high temperatures due to formation of atomic terraces on the substrate surface. The photoluminescence signals also increases with the increasing annealing temperature of the substrate.