直流磁控溅射ZnO薄膜的结构和室温PL谱研究

ZnO是一种新型的宽带化合化半导体材料，对短波长的光电 子器件如UV探测器，LED和LD有着巨大的潜在应用。本实验研究采用直流反应磁控溅射法在硅衬底上沉积C轴择优取向的ZnO晶体薄膜，薄膜呈柱状结构，晶粒大小约为100nm，晶粒内为结晶性能完整的单晶，但晶粒在C轴方向存在较大的张应力。ZnO薄膜在He-Cd激光器激发下有较强的紫外荧光发射，应力引起ZnO禁带宽度向长波方向移动，提高衬底温度有利于降低应力和抑制深能级的绿光发射。     

透明导电薄膜ZnO∶Mn的低温制备及性能研究

利用直流磁控溅射法在室温玻璃衬底上制备出了可见光透过率高、电阻率低的掺锰氧化锌(ZnO∶Mn)透明导电薄膜。实验制备的ZnO∶Mn为六方纤锌矿结构的多晶薄膜,且具有垂直于衬底方向的c轴择优取向。实验结果表明,靶与衬底之间的距离对ZnO∶Mn薄膜的生长速率、残余应力及电学性能有很大影响,而对薄膜的晶粒尺寸和光学性能影响不大。考虑薄膜的电学、光学及力学性能,认为靶与衬底之间的最佳距离为7.0 cm。在此条件下制备的ZnO∶Mn薄膜的电阻率达到4.2×10-4Ω.cm,可见光透过率为86.6%,而残余应力仅为-0.025 GPa。     

透明导电薄膜ZnO:Mn的低温制备及性能研究

利用直流磁控溅射法在室温玻璃衬底上制备出了可见光透过率高、电阻率低的掺锰氧化锌(ZnO:Mn)透明导电薄膜.实验制备的ZnO:Mn为六方纤锌矿结构的多晶薄膜,且具有垂直于衬底方向的c轴择优取向.实验结果表明,靶与衬底之间的距离对ZnO:Mn薄膜的生长速率、残余应力及电学性能有很大影响,而对薄膜的晶粒尺寸和光学性能影响不大.考虑薄膜的电学、光学及力学性能,认为靶与衬底之间的最佳距离为7.0 cm.在此条件下制备的ZnO:Mn薄膜的电阻率达到4.2×10-4 Ω·cm,可见光透过率为86.6％,丽残余应力仅为-0.025 GPa.     

衬底温度对ZnO薄膜生长过程及微观结构的影响研究

以醋酸锌水溶液为前驱体,采用改进的超声喷雾热解法在Si(100)衬底上沉积ZnO薄膜,以X射线衍射(XRD)、扫描电镜(SEM)等手段分析所得ZnO薄膜的晶体结构和微观形貌,着重考察了衬底温度对ZnO薄膜生长过程及微观结构的影响.结果表明,在衬底温度为500℃下所得ZnO薄膜表面均匀光滑,属六方纤锌矿结构,且沿c轴择优生长,晶粒尺寸的为40～50nm;衬底温度对ZnO薄膜生长过程影响显著,随衬底温度的升高,薄膜生长速率存在一极限值,且ZnO薄膜的c轴取向趋势增强,晶粒尺寸得到细化.     

玻璃衬底和Si衬底制备的Zn0.96Nd0.04O薄膜的结构研究

通过射频磁控溅射技术在玻璃衬底和Si（111）村底上制备了Zn0.96Nd0.04O薄膜。XRD分析表明,Zn0.96Nd0.04O薄膜是具有C轴择优生长的纳米多晶薄膜,Nd以替位原子的形式存在于ZnO晶格,Nd掺杂没有改变ZnO晶格结构。从AFM图中看出,薄膜表面形貌较为粗糙,Si衬底薄膜的晶粒具有规律且晶粒尺寸大于玻璃衬底。     

脉冲激光沉积法室温下ZnO薄膜的制备与表征

在室温条件下,采用脉冲激光沉积技术在玻璃衬底上生长了ZnO薄膜.对薄膜的XRD分析表明,ZnO薄膜为六方纤锌矿结构并沿c轴取向生长,且(002)衍射峰的半高峰宽仅为0.24°.薄膜沿c轴方向受到一定的张应力为1.7×108 N/m2.原子力显微镜分析表明薄膜表面较为平整,平均粗糙度约为6.5 nm,晶粒尺寸约为50 nm.此外,透射光谱分析表明薄膜的禁带宽度为3.25 eV,与ZnO体材料的禁带宽度3.30 eV基本相同.     

不同衬底上ZnO薄膜的射频磁控溅射制备及结构

利用射频磁控溅射镀膜的方法,在c面蓝宝石、石英玻璃和载破片衬底上成功制备了ZnO薄膜。用x射线衍射和扫描电子显微镜进行了结构分析并观察了样品的表面形貌。结果表明：制备的ZnO薄膜具有良好的C轴择优取向结晶度,并在石英玻璃和载玻片衬底上的ZnO薄膜表面发现了[101]取向的“米粒状”晶粒。     

衬底温度对PLD方法生长的ZnO薄膜结构和发光特性的影响

在不同的衬底温度下, 通过脉冲激光淀积的方法在Si衬底上生长出c轴高度取向的ZnO薄膜. ZnO薄膜的结构和表面形貌通过X射线衍射和原子力显微镜表征. 同时以He-Cd激光和同步辐射作为激发源来测试样品的发光特性. 实验结果表明, 在衬底温度为500℃时生长的ZnO薄膜具有非常好的晶体质量, 并且表现出很强的紫外发射. 在用同步辐射为激发源的低温(18K)光致发光谱中, 还观察到了一个位于430nm处的紫光发射, 我们认为这个紫光发射与存在于晶粒间界的界面势阱所引起的缺陷态有关, 这个势阱可能起源于Zn填隙(Zn _i)     

TiO_2过渡层对Si基ZnO薄膜光致发光特性的影响

采用直流反应溅射法在Si(100)衬底上制备了有TiO2过渡层的ZnO薄膜,并与直接在Si上生长的样品进行比较。通过X射线衍射技术和光致发光谱等分别对ZnO薄膜的结构和光学性质进行测量和分析。测量结果表明,引入过渡层后ZnO薄膜的平均晶粒尺寸变大,晶粒间界变少,结晶质量提高,薄膜内的应力得到一定程度的释放。此外,室温光致发光谱表明过渡层使ZnO薄膜的紫外发射明显增强,并研究和分析了其微观机理。     

衬底温度对PLD法制备ZnO薄膜结构及发光特性的影响

在60Pa的高氧压气氛中,用脉冲激光沉积法以Si(111)为衬底在不同温度下制备了ZnO薄膜.RHEED和XRD结果表明,所有样品都是c轴高度择优取向的多晶ZnO薄膜.随衬底温度的升高,ZnO薄膜(002)衍射峰的半高宽不断减小,从0.227～0.185°.对(002)衍射峰的2θ值分析表明,650℃下生长的ZnO薄膜几乎处于无应力的状态,而在较低或较高温度下生长的薄膜中都存在着一定程度的c轴压应力.室温PL谱测试说明在650℃生长的ZnO薄膜具有最强的紫外发射峰和最窄的UV峰半高宽(83meV).在700℃得到的样品PL谱中,检测到一个位于3.25eV处的低能发射峰.经分析,该峰可能是来自于施主-受主对(DAP)的跃迁.     

Low temperature annealing effects on the structure and optical properties of ZnO films grown by pulsed laser deposition

ZnO thin films were deposited on glass substrates at room temperature (RT) ∼500 °C by pulsed laser deposition (PLD) technique and then were annealed at 150-450 °C in air. The effects of annealing temperature on the microstructure and optical properties of the thin films deposited at each substrate temperature were investigated by XRD, SEM, transmittance spectra, and photoluminescence (PL). The results showed that the c-axis orientation of ZnO thin films was not destroyed by annealing treatments; the grain size increased and stress relaxed for the films deposited at 200-500 °C, and thin films densified for the films deposited at RT with increasing annealing temperature. The transmittance spectra indicated that E_g of thin films showed a decreased trend with annealing temperature. From the PL measurements, there was a general trend, that is UV emission enhanced with lower annealing temperature and disappeared at higher annealing temperature for the films deposited at 200-500 °C; no UV emission was observed for the films deposited at RT regardless of annealing treatment. Improvement of grain size and stoichiometric ratio with annealing temperature can be attributed to the enhancement of UV emission, but the adsorbed oxygen species on the surface and grain boundary of films are thought to contribute the annihilation of UV emission. It seems that annealing at lower temperature in air is an effective method to improve the UV emission for thin films deposited on glass substrate at substrate temperature above RT.     

Structural, Morphological and Optical Properties of ZnO Thin Films Grown on γ-LiAlO2 Substrate by Pulsed Laser Deposition

ZnO thin films were deposited on the substrates of (100) γ-LiAlO2 at 400, 550 and 700℃ using pulsed laser deposition (PLD) with the fixed oxygen pressure of 20 Pa, respectively. When the substrate temperature is 400℃, the grain size of the film is less than 1 μm observed by Leitz microscope and measured by X-ray diffraction (XRD). As the substrate temperature increases to 550℃, highly-preferred c-orientation and high-quality ZnO film can be attained.While the substrate temperature rises to 700℃, more defects appears on the surface of film and the ZnO films become polycrystalline again possibly because more Li of the substrate diffused into the ZnO film at high substrate temperature. The photoluminescence (PL) spectra of ZnO films at room temperature show the blue emission peaks centered at 430 nm. We suggest that the blue emission corresponds to the electron transition from the level of interstitial Zn to the valence band. Meanwhile, the films grown on γ-LiAlO2 (LAO) exhibit green emission centered at 540 nm, which seemed to be ascribed to excess zinc and/or oxygen vacancy in the ZnO films caused by diffusion of Li from the substrates into the films during the deposition.     

Epitaxial growth of ZnO films on (100) and (001) γ-LiAlO2 substrates by pulsed laser deposition

Structural and optical properties were investigated for ZnO films grown on (100) and (001) γ-LiAlO₂ (LAO) substrates by pulsed laser deposition method. According XRD results, it is intuitionistic that (100) LAO is suitable for fabricating high quality ZnO film, while (001) LAO is unsuitable. The FWHM of XRD, stress in film and FWHM of UV PL spectra for ZnO films on (100) LAO show a decreasing with increasing substrate temperature from 300 to 600 °C. ZnO film fabricated at 600 °C has the greatest grain size, the smallest stress (0.47 Gpa) and PL FWHM value (∼85 meV). This means that the substrate temperature of 600 °C is optimum for ZnO film deposited on (100) LAO. Moreover, it was found that the UV PL spectra intensity of ZnO film is not only related to the grain size and stoichiometric, but also depends on the stress in the film.     

The effects of substrate temperature on the structure and properties of ZnO films prepared by pulsed laser deposition

ZnO thin films were prepared by pulsed laser deposition (PLD) on glass substrates with growth temperature from room temperature (RT) to 500 °C. The effects of substrate temperature on the structural and optical properties of ZnO films have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission spectra, and RT photoluminescence (PL) measurements. The results showed that crystalline and (0 0 2)-oriented ZnO films were obtained at all substrate temperatures. As the substrate temperature increased from RT to 500 °C, the ratio of grain size in height direction to that in the lateral direction gradually decreased. The same grain size in two directions was obtained at 200 °C, and the size was smallest in all samples, which may result in maximum E_g and E₀ of the films. UV emission was observed only in the films grown at 200 °C, which is probably because the stoichiometry of ZnO films was improved at a suitable substrate temperature. It was suggested that the UV emission might be related to the stoichiometry in the ZnO film rather than the grain size of the thin film.     

High optical quality ZnO films grown on graphite substrate for transferable optoelectronics devices by ultrasonic spray pyrolysis

ZnO thin films were deposited on graphite substrates by ultrasonic spray pyrolysis method. The effects of substrate temperature and film thickness on the crystalline structure, morphology, and optical properties of the as-grown ZnO films were investigated systemically. Results illustrated that dense ZnO films with hexagonal wurtzite structure were uniformly distributed on the substrate. Strong near-band edge ultraviolet (UV) emission peaks were observed in room temperature photoluminescence (PL) spectra for the samples prepared under optimized parameters, yet the usually observed defect related deep level emissions were nearly undetectable, indicating high optical quality ZnO films could be achieved via this easy process under optimal conditions. The successful growth of polycrystalline ZnO films on graphite offers the significant opportunity to be readily transferred onto any rigid or flexible foreign substrates, since the graphite substrates consist of weakly bonded layer structure.     

Temperature dependence of ZnO thin films grown on Si substrate

The structural and optical properties of ZnO thin films grown on Si substrates were investigated for different growth temperatures in the range of 520–720 °C. X-ray diffraction investigations revealed the preferred c-axis oriented growth of ZnO thin films, which was further confirmed by the presence of ZnO (0002) diffraction spots with arc shape. The increase in growth temperature transformed surface morphology from pyramidal with columnar grains to relatively flat surface with increased grain size. In addition, the increased growth temperature caused redshift and intensity enhancement of band-edge emission of the ZnO, which were related to the increase in tensile strain and the grain size, respectively.     

Effects of buffer layer thickness on properties of ZnO thin films grown on porous silicon by plasma-assisted molecular beam epitaxy

ZnO thin films with different buffer layer thicknesses were grown on Si and porous silicon (PS) by plasma-assisted molecular beam epitaxy (PA-MBE). The effects of PS and buffer layer thickness on the structural and optical properties of ZnO thin films were investigated by atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and photoluminescence (PL). The ZnO buffer layers, the intensity of the (002) diffraction peak for the ZnO thin films and its full width at half maximum (FWHM) decreased with an increase in the thickness of the ZnO buffer layers, indicating an improvement in the crystal quality of the films. On introducing PS as a substrate, the grain sizes of the ZnO thin films became larger and their residual stress could be relaxed compared with the ZnO thin films grown on Si. The intensity ratio of the ultraviolet (UV) to visible emission peak in the PL spectra of the ZnO thin films increased with an increase in buffer layer thickness. Stronger and narrower UV emission peaks were observed for ZnO thin films grown on PS. Their structural and optical properties were enhanced by increasing the buffer layer thickness. In addition, introduction of PS as a substrate enhanced the structural and optical properties of the ZnO thin films and also suppressed Fabry-Perot interference.     

Properties of ZnO:Al films deposited on polycarbonate substrate

Transparent conducting aluminum-doped zinc oxide (ZnO:Al) films have been prepared on polycarbonate (PC) substrates by pulsed laser deposition technique at low substrate temperature (room-100 °C); Nd-YAG laser with wavelength of 1064 nm was used as laser source. The experiments were performed at various oxygen pressures (3 pa, 5 pa, and 7 Pa). In order to study the influence of the process parameters on the deposited (ZnO:Al) films, X-ray diffraction and atomic force microscopy were applied to characterize the structure and surface morphology of the deposited (ZnO:Al) films. Polycrystalline ZnO:Al films having a preferred orientation with the c-axis perpendicular to the substrate were deposited with a strong single violet emission centering about 377–379 nm without any accompanying deep level emission. The average transmittances exceed 85% in the visible spectrum for 300 nm thick films deposited on polycarbonate.     

Influence of substrate temperature on ultraviolet emission of ZnO films prepared by ultrasonic spray pyrolysis

ZnO films were deposited on MgO substrates (ZnO/MgO) by ultrasonic spray pyrolysis. Substrate temperature varied from 200 to 350°C. The crystallographic properties and surface morphologies of the ZnO/MgO films were studied by X-ray diffraction and scanning electron microscopy. The properties of photoluminescence (PL) for the films were investigated by dependence of PL spectra on the substrate temperature and the ambient temperature. Ultraviolet (UV) emission peak (3.37 eV) was dominantly detected at 18 K, which sustained at 300 K with a reduced value of the peak energy. The ZnO/MgO films prepared at 350°C showed the strongest UV emission peak at 18 and 300 K among the films in this study.