P-MBE方法在硅衬底上制备的氧化锌薄膜及纳米管的结构和光学性质的研究

【作者】 颜建锋；

【导师】 刘益春； 吕有明；

【作者基本信息】 东北师范大学 ， 理论物理， 2004， 硕士

【摘要】 氧化锌作为一种重要的具有六方结构的 II-IV 族宽带隙(3.3eV)半导体材料，由于具有较高的激子束缚能高(60meV)，在室温下容易获得强的激子发射，被认为是制作紫外半导体激光器的合适材料。因此，对氧化锌材料的研究已成为继 GaN 之后，宽带隙半导体材料在光电子领域中又一个研究的热点。 人们已采用分子束外延技术获得了高质量的氧化锌薄膜材料，但其衬底材料一般选择为 Al2O3，而对在 Si 衬底上的 ZnO 薄膜材料的生长和特性研究的较少。本文主要利用等离子体辅助分子束外延的方法在 Si 衬底上生长 ZnO 以及对其结构和光学性质进行研究。具体内容包括三个方面：1. 研究了衬底温度对氧化锌薄膜质量的影响。在 350℃-700℃温度范 围内生长了一系列 ZnO 薄膜。结果表明在较低的温度下，被吸附 到衬底上的原子由于迁移能力较低不易占据到正常的格位上，导致 晶体的结晶性下降；而在较高温度下(>650℃)，吸附系数较低的氧 原子容易从衬底表面脱附，而在薄膜中形成大量的氧空位。在我们 的实验条件下，X 射线衍射和光致发光结果表明最佳的生长温度为 550℃。通过变温光谱把室温下紫外发光的起因归结为自由激子发 射。2. 研究了低温缓冲层对 ZnO 薄膜结构和光学性质的影响。在 300℃温 度下生长了一层 ZnO 薄膜，由于生长温度较低 Zn、O 原子容易被 吸附到衬底的表面导致非定形的 ZnO 的生长，有效减缓了衬底与 ZnO 之间的晶格失配带来的影响，降低了失配位错和缺陷的产生。 X 射线衍射、原子力显微镜、RHEED 和光致发光的结果表明，在 低温缓冲层上选择最佳温度(550℃)生长 ZnO，无论是样品的表面形 貌，结构还是样品的光学性质都得到了明显的改善。由此，我们得 出结论，低温缓冲层的引入很好的提高了 ZnO 薄膜的质量。3. 研究了低维 ZnO 薄膜结构的制备及其性质。通过氧等离子体处理 衬底上生长的 ZnO 薄层得到环状的“模板”结构，在 Si 衬底上得到 i<WP=4>了 ZnO 纳米管，在这里氧等离子处理最为关键。ZnO 纳米管的场发射阈值电场为 2.5V/μm。当电场是 7V/μm 时，发射电流密度可以达到 1mA/cm2。样品表现出了高的电流密度和低的发射阈值电场，这也为 ZnO 在平板显示和场发射方面应用提供了可能。更多还原

【Abstract】 As an important II-VI compound semiconductor of wurtzite crystalstructure with the wide band-gap of 3.3eV and large exciton bindingenergy of 60meV, which ensures the high efficient excitonic emission atroom temperature, Zinc oxide (ZnO) is regarded as one of the mostpromising materials for fabricating efficient ultraviolet (UV) and blue lightemitting devices. Like GaN compound of wide band gap, the researchabout ZnO has burned white hot in the field of opto-electronics. High quality ZnO thin films have been grown on Al2O3 substrate byMBE. But few studies have been focused on the growth andcharacterization of ZnO grown on Si substrate which will be done in thisdissertation, because Silicon (Si) as another promising substrate is not onlyof interest for the integration of optoelectronic devices but also cheaperand easier to cleave in comparison to sapphire. The major results are givenas following:1. Dependence of ZnO thin films on the substrate temperature has been studied. A series of ZnO thin films are grown on Si substrate with increasing substrate temperature for temperature ranging from 350°C to 700. The results indicate that the qualities of the ZnO thin films grown at low substrate temperatures decrease, because the transfer rate of atoms absorbed on the substrates is too low to transfer to the normal state of the ZnO crystal lattice at the low growth temperature; and the qualities of the ZnO thin films grown at high (>650°C) substrate temperatures is also poor, because the atoms absorbed on the substrate is easy to escape from the substrate. The results of XRD and PL spectra at our experiments indicate that 550 is the optimal deposition temperature for growth of ZnO thin films on Si(111) substrates by P-MBE. And the origin of the ultraviolet luminescence is ascribed to the emission of the free exciton. iii<WP=6>2. Effect of ZnO buffer layer grown at a low-temperature on the quality of ZnO thin films has also been studied. The low temperature buffer layer was epitaxied on the Si substrate at the temperature of 300°C. Non-finite ZnO was grown on the substrate due to the low temperature at which the Zn and O atoms is easy to be absorbed on the substrata, which could relaxed effectively the effects of the lattice mismatch between the substrate and ZnO thin films on the quality of the ZnO films and could reduce the formation of distortion and defects. The results of XRD, AFM, RHEED and PL spectra tell us that the morphology, structure and optical qualities of the ZnO thin film grown on the low-temperature buffer layer at the optimal substrate temperature of 550°C have been improved greatly, which indicates us that high-quality ZnO thin films can be obtained on Si substrate by growing on top of a low-temperature grown ZnO buffer layer.3. Growth and characterization of ZnO nanotube on Si substrate has been studied. The ZnO nanotubes on Si substrate have been obtained via treatments of the initial thin film ZnO layer by -plasma which provides a template to grow ZnO nanotubes. Here O2 -plasma treatment is the + crux to grow ZnO nanotubes on Si substrate. These ZnO nanotubes show excellent field emission properties with turn-on voltage of 2.5 V/μm. The emission current density of ZnO nanotubes is 1mA/cm2 at a bias field of 7V/μm.The ZnO nanotubes grown on Si substrate with high current emission and low turn-on voltage makes the use of ZnO on display and field emission possible.更多还原