【作者】 王兆阳；

【导师】 胡礼中；

【作者基本信息】 大连理工大学 ， 光学工程， 2006， 博士

【摘要】 氧化锌（ZnO）是一种直接带隙宽禁带（3.37eV）Ⅱ-Ⅵ族化合物半导体材料,具有较大的激子束缚能（60 meV）,理论上可以在室温下实现紫外光的受激发射。同时,ZnO还是优质的压电、气敏及光电材料。ZnO薄膜的制作方法很多,传统方法有:磁控溅射（magnetron sputtering）、化学气相沉积（CVD）、溶胶凝胶法（sol-gel）、喷雾热解法（spay pyrolysis）、热氧化法（thermal oxidation）、分子束外延（MBE）等,新的生长技术如脉冲激光沉积（PLD）、金属有机物化学气相沉积（MOCVD）、原子层外延生长法（ALE）、激光分子束外延（L-MBE）等也开始广泛应用。由于ZnO在结构、能带、电学和光学方面的诸多优点,加上ZnO薄膜的制作方法很多,可以适应不同的应用需求,ZnO在器件应用方面具有广阔的应用范围,潜力很大,前景极好。它可以被用来制作透明电极、压敏电阻、太阳能电池窗口、表面声波器件、气体传感器、发光二极管等。在短波区域,ZnO可用于制造紫外发光器件和紫外激光器,对于提高光记录密度及光信息的存取速度起着非常重要的作用。 脉冲激光沉积是近年来发展起来的先进的薄膜生长技术,能够制备出高质量的薄膜。它的工作原理是在高真空背景下用高能激光烧蚀ZnO靶材生成蒸发物淀积在加热衬底上生长晶体薄膜。有多种衬底可以生长ZnO薄膜,目前使用最多的是Al₂O₃衬底,已经以Al₂O₃为衬底制备出高质量的ZnO薄膜。而Si是最重要和使用最广泛的半导体材料,它的优点是价格便宜,已经拥有成熟的加工工艺。本论文中用脉冲激光沉积方法在Si（111）衬底上按照衬底温度、脉冲激光重复频率、环境氧压等不同条件生长了ZnO薄膜,并用X射线衍射（XRD）、荧光光谱（PL）、扫描电子显微镜（SEM）、原子力显微镜（AFM）以及台阶仪和电子探针等测试手段进行了表征。根据对ZnO薄膜的结构和发光特性的研究,找到了生长薄膜的优化条件,得到了高度c-轴（002）取向的结晶质量较高的ZnO薄膜。发现在温度为650℃左右、氧压50Pa左右、频率5Hz左右的范围内能生长出结晶质量较好的薄膜,并能得到半高宽较窄,强度较大的紫外发光峰。 同时研究了ZnO薄膜的发光机理,认为薄膜紫外峰源自自由激子复合发光,绿光峰的发光机制与锌位氧O_zn关系密切,氧空位是蓝光发射的重要原因。 PLD方法的一个优点是可以对生长的薄膜进行原位监测,反射式高能电子衍射仪（RHEED）是本试验中用来对ZnO薄膜生长进行原位监测的重要仪器。通过观察研究了ZnO薄膜的生长方式,对观测到的Si（111）衬底和Al₂O₃衬底的RHEED图像进行了结构分析,发现了ZnO薄膜的两种RHEED电子衍射点阵并对它们进行了标定。更多还原

【Abstract】 ZnO is a compound semiconductor with wide direct band gap of 3.37eV and a large exciton binding energy of 60meV at room temperature. Theoretically, it can realize stimulated ultraviolet （UV） emission at room temperature. ZnO is also an ascendant piezoelectric, gas sensitive and optoelectronic material. There are many growth methods for ZnO films such as magnetron sputtering, chemical vapor deposition, sol-gel, spay pyrolysis, thermal oxidation and molecular beam epitaxy （MBE）. Recently, some new growth methods such as pulsed laser deposition （PLD）, metal organic chemical vapor deposition （MOCVD）, atomic layer epitaxy and laser molecular beam epitaxy have been widely used. Because ZnO thin film has so many advantages in structural and electrical properties and can be grown through many methods, it can suit many different applied demands. ZnO thin films can be used to fabricate transparency electrode, piezoresistor, cell battery window, surface acoustic wave device, gas sensor and light-emitting diode etc.. In short wave region, ZnO can be used to fabricate UV light emitting and UV laser devices, which is very important for improvement of memory density and optical information access speed.PLD is a newly developed film growth technique which can fabricate high-quality films. In this technique, high density laser ablates the target and produces ZnO plume depositing on heated substrate in high vacuum background. Many kinds of substrates can be used to grow ZnO thin films. At present, the most abroad used substrate is Al₂O₃ and high-quality ZnO films have been obtained on it. Si is the most important and abroad used semiconductor material. It is cheap in price and has mature processing technique. In this paper, ZnO films were prepared on Si （111） substrates at various substrate temperatures, pulsed laser repetition frequencies and oxygen pressures. The films were examined by X-ray diffraction （XRD）, photoluminescence spectra （PL）, scan electron microscopy （SEM）, atomic force microscopy （AFM）, surface profiler and electronic probe. Through the research of the structural and optical properties of ZnO films, optimized conditions for growing ZnO films were obtained. The results suggested that high quality ZnO films with highly c-axis oriented can be prepared by PLD. The narrower and stronger UV peak of ZnO films with excellent crystallinity can be found from the samples grown at about 650°C, 50Pa and 5Hz.Light emission mechanics of ZnO films were also studied. It is found that the UV emission is origin from free exciton recombination radiation. The green peak is closely relatedwith oxygen atom at the zinc position in the crystal lattice, OZn and blue peak is from oxygen vacancy, Vo.One of the merits of PLD technique is that the growth of films can be monitored in situ. In our experiments, we observed the growth of ZnO thin films maily using reflection high-ernergy electron diffraction instrument. The growth procedure of ZnO thin films was examined by RHEED and the growth mode of ZnO films was analysed. The RHEED images of Si （111） and A12O3 substrates were analysed in structure. Two kinds of RHEED electron diffraction dot matrixes of ZnO films were found and indexed.MgO has a band gap of about 6.7eV and different optical index of refraction with ZnO. For the purpose of modulating the ernergy band gap structure and light emission properties of ZnO and making Bragg reflector to improve the UV emission of ZnO films using their different optical index of refraction, ZnO/MgO multilayer films with different growth periods were fabricated using ZnO and MgO targets. The structure and the PL properties of ZnO/MgO multilayer films were explored. Compared with highly c-axis orientation ZnO films, in the multilayer films the position of （002） peak of ZnO have a excursion toward larger diffraction angle and UV peak of ZnO have a blue shift because of the doping of Mg. These made the energy band gap of ZnO in multilayer films increas about 0.05 eV than that of ZnO films. From TEM images, the film is found to be polycrystal grains and have more crystal direction than ZnO films. In TEM images, the crystal characters and area distribution of the multilayer films were obtained. The TEM images suggest that the doping of Mg atoms into ZnO lattice resuted in that distorted lattice in the （001） plane and the increase of lattice constant a and the decrease of lattice constant c of hexangular ZnO. The other area formed MgO and ZnxMgi.xO polycrystal grains determined by the different diffusion extent. All these work made a primary foundation for later research.更多还原