【作者】 张军；

【导师】 谢二庆；

【作者基本信息】 兰州大学 ， 凝聚态物理， 2007， 博士

【摘要】 氧化锌（ZnO）是一种新型宽禁带直接带隙Ⅱ-Ⅵ族半导体材料，室温下的禁带宽度为3.37 eV，激子束缚能高达60 meV，比同为宽禁带半导体的ZnSe（22meV），ZnS（40 meV）和GaN（25 meV）都高很多。这些特性使ZnO在室温下可以产生很强的光致激子紫外发射，有利于研制高效率发光二极管（LED）、紫外探测器、蓝紫光LED和LD等短波长光电器件。同时，ZnO的能带结构与TiO₂相似，在紫外光照射下，ZnO薄膜可以产生电子-空穴对，在薄膜表面形成强的氧化-还原体系，对空气或水溶液中的有机物源进行氧化降解。故ZnO可以作为一种很有前途的光催化材料。此外，在太阳能电池工艺中，ZnO薄膜也有很好的应用前景：在ZnO薄膜中进行Ⅲ族（Al、Ga、In）元素掺杂，可以使其在可见光区的光透过率增强（高达90％），且具有良好的导电性，这些优点使ZnO材料可作为太阳能电池窗口材料。针对ZnO薄膜材料在以上不同领域中的应用前景，本论文开展了相应的研究工作。利用氧化法制备纳米ZnO薄膜的光催化研究，溅射法制备Al掺杂的ZnO透明导电薄膜，原位热氧化氮化锌（Zn₃N₂）工艺制备p型ZnO薄膜，并研究了制备工艺、掺杂以及结构对其性能的影响。为了有效提高薄膜的孔隙率并增强其光催化性能，本论文利用两步氧化法制备了ZnO薄膜。即先在纯氧气氛中低于金属锌（Zn）熔点的温度下对制备的Zn膜进行初步氧化，然后再提高氧化温度进行二次氧化。通过降解苯酚实验分析表明，两步氧化法制备的样品的光催化性能优于一般氧化法得到的样品。本研究工作为性能良好且成本低廉的ZnO光催化剂的制备找到了一条很好的途径。对于ZnO基透明导电膜在太阳能电池中的应用，本工作以金属Zn和铝（Al）为靶材，采用射频（RF）反应共溅射技术在低温（200℃）玻璃衬底上沉积了铝掺杂氧化锌（ZnO：Al）薄膜。对制备样品的形貌结构、组成成分和光学电学特性进行了分析表征。结果表明，我们成功制备了定向（002）生长的六角纤锌矿结构的ZnO：Al薄膜，其可见光透过率达85％，电阻率在10^-1～10³Ω·cm之间。该薄膜的性能基本符合光电器件，特别是薄膜太阳电池窗口层的应用要求，并易于规模化工业生产。制备导电性良好的p型ZnO薄膜是发展ZnO基光电器件的重要因素。本论文采用射频磁控溅射法在不同衬底温度和不同气氛下制备了Zn₃N₂薄膜，然后在低压氧气氛下进行原位热氧化制备N掺杂的ZnO薄膜。利用各种表征方法分别对Zn₃N₂薄膜和ZnO薄膜进行了分析。结果表明，衬底温度为200℃时制备的Zn₃N₂薄膜，在500℃下氧化2小时可以得到电阻率为0.7Ω·cm，空穴浓度为10¹⁷cm^-3，空穴迁移率为0.9cm²／V·s的具有c轴择优取向的p型ZnO薄膜。获得的p型ZnO薄膜还具有良好的光学特性，紫外可见光范围内透过率为85％，处于紫外区域的激子复合产生的发光峰很强。以上可见，原位氧化工艺制备的p型ZnO薄膜质量较好，重复性好。通过进一步改进工艺，有望制备出性能稳定、载流子浓度高的低阻p型ZnO薄膜。考虑到新一代半导体材料与Si基半导体产业的兼容性，本工作还对优良的衬底材料碳化硅（SiC）进行了初步研究。利用射频磁控溅射法在石英衬底上制备了纳米SiC薄膜，薄膜表面由尺寸为50～90nm的SiC纳米颗粒组成。总之，本论文所涉及的研究工作极大地丰富了不同领域ZnO材料的制备途径，将为ZnO材料的产业化起到重要的推动作用。更多还原

【Abstract】 Znic Oxide （ZnO） is a wide direct band-gap （3.37eV） II-VI semiconductor material with a large exciton binding energy of 60 meV at room temperature, which is much higher than most other semiconductors, such as ZnSe （22 meV）, ZnS （40 meV） or GaN （25 meV） . So ZnO is a proper ultraviolet material for short-wavelength photoelectrical device: high efficient light emitting diode （LED）, UV detector, and blue LED .etc. Meanwhile, similar with the titanium oxide （TiO₂）, after UV light irradiation the surface of ZnO films can produce the electron-hole pairs as reductant-oxidant, which can degrade the organic pollutants in environment. So ZnO film could be as a promising photocatalysis material. As for the solar cell application, ZnO has some advantages: doping with III elements（Al、Ga、In）, ZnO-based material could be used as window coats with high transmission ratio in visible light and low resistivity. In this paper, the ZnO films for functional perspective, were successfully prepared by two-step oxidization method, RF sputtering technique, oxidization of Zn₃N₂ films method and in situ oxidization of Zn₃N₂ films, and the different characters of films were investigated by many methods.The ZnO films prepared by two-step oxidization method is shown below: first, Zn films, which prepared by evaporation, were oxidated at oxygen atmosphere below the melt-pointing of metal Zn, and then, the films were continued oxidization at high temperature. The photoactive capability of ZnO films was investigated by degradation of phenol method. The analysis showed that the ZnO films prepared by two-step oxidation show higher photoactive characteristic than that prepared by direct oxidation method. This is ascribed that two-step oxidization method improves the interstitial rate of the films. Excellent adhesion as well as being recyclable and efficient in phenol degradation of ZnO films was found in our experiment, which is in favor of ZnO films used in photocatalysis field.By the co-sputtering method using the metal Zn and Al targets, the ZnO:Al films were deposited on glass substrates. The effects of oxidation temperature and time on structural, electronical and optical properties of the samples were investigated by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, Hall-effect measurements, UV-Vis transmittance spectra and photoluminescence（PL） spectra. The results indicated highly quality wurtzite ZnO:Al films with （002） orientation were successfully fabricated, which presented high transmittance rate （above 85%） and low resistivity (10^-1～10^-3Ω·cm). The properties of films could be satisfied with the photoelectrical coats in devices fields, especially in solar cells as window coats. Moreover, the films could be produced by this method, which also be extended to other fields.For development of ZnO-based opto-electrical devices, the fabrication of p-type ZnO is of important significance. Low resistance p-type ZnO thin films were prepared by in situ oxidation of Zn₃N₂ films which is deposited by reactive RF magnetron sputtering of zinc in Ar-N₂ mixture atmosphere. The effects of oxidation temperature and time on structural, electronic and optical properties of the samples were investigated by X-ray diffraction, scanning electron microscopy, Hall-effect measurements, UV-Vis transmittance spectra and PL spectra. It was found that the sample which oxidized at 450℃presented Zn₂N₃ structure except for ZnO; the sample at 500℃for 2 hours had better properties: low resistance （0.7Ω·cm）, high transmittance rate （above 85%）, predominant excitonic ultraviolet emission with narrow full width at half maximum and weak deep levels visible emission. The low resistance p-type ZnO films could be used as short wavelength devices in industrial fields.Except for the ZnO-based films in this paper, considering of the compatibility with Si-based technology, the SiC films, as excellent substrate materials, were also fabricated by RF sputtering and investigated by some measurements.These researches on ZnO materials are valuable for the fabrication of p-type ZnO films. By the amendment and improvement of in situ oxidization, the realization of ZnO-based opto-electrical devices could be developed in near future.更多还原