论文标题:纳米氧化锌薄膜的结构和光学特性研究
The Study on Structure and Optical Properties of Nanocrystalline ZnO Thin Films
论文作者 张喜田
论文导师 许武；刘益春,论文学位 博士,论文专业 凝聚态物理
论文单位 中国科学院研究生院（长春光学精密机械与物理研究所）,点击次数 1027,论文页数 97页File Size6179k
2002-04-01论文网 http://www.lw23.com/lunwen_100502/ 受激发射;光致发光; 纳米氧化锌薄膜; 激子;可见发光机制;热氧化
Stimulated Emission;Photoluminescence; Nanocrystalline ZnO Thin Films; Exciton; Visible Luminescence Mechanism; Thermal Oxidation
氧化锌是一种重要的宽禁带隙（3.3 eV）半导体材料，它的激子束缚能高达60 meV。因此，氧化锌材料在紫外光电器件方面有巨大的应用潜力。目前，有关氧化锌研究部分集中在氧化锌的紫外激光发射和可见发光机制方面。尽管研究小组提出了很多不同的可见发光机制，但尚没有统一的认识。当然,实现紫外激光发射是人们希望达到的目标。针对这两方面问题我们做了如下研究：利用低压金属有机化学气相沉积（LP-MOCVD） 工艺，首先在二氧化硅衬底上生长纳米ZnS薄膜，然后，在不同温度下进行热氧化处理。X射线衍射（XRD）和拉曼实验结果表明硫化锌（ZnS）薄膜在高于700 oC热氧化处理后，硫化锌（ZnS）全部转化为氧化锌（ZnO），且是六角纤锌矿的多晶薄膜。光致发光（PL）结果表明，样品在900 oC退火时紫外（380 nm）发光最强，可见发射最弱。我们详细地讨论了退火温度对紫外光发射的影响。提出紫外伴随低能带尾发光是由束缚激子发射与自由激子发射叠加的缘故。利用飞秒激光器作为光泵浦激发光源，研究了氧化锌薄膜的光泵浦受激发射，当条形光斑辐照薄膜样品时，将沿着光斑条由氧化锌纳米晶面自然地形成光学谐振腔，由于平面介质波导结构限制光散射，所以成功地观测到二氧化硅衬底上的纳米氧化锌（ZnO）薄膜的紫外受激发射。在可见发光机制探讨中，为了证明氧空位或缺陷是分布在纳米晶表面，我们提出氧化锌中掺杂锰（ZnO：Mn），研究了ZnO：Mn薄膜的光致发光（PL）。结合发光光谱、X射线光电子能谱（XPS）和电子顺磁共振（EPR）结果，提出了核-壳氧化锌（ZnO）结构。在本论文中提出可见发光中心是Vo**和[Vo*，electron]或[Vo**，two electrons]复合体。纳米氧化锌（ZnO）表面的钝化实际上是在氧化锌（ZnO）的核和表面之间形成了大的势垒阻止表面缺陷捕获光生电子或光生空穴形成发光中心Vo**和[Vo*，electron]或[Vo**，two electrons]复合体，同时，提出了一种新的可见发光机制，很好地解释了实验中观察到的现象。
Zinc oxide (ZnO) is an interesting wide band gap (3.3 eV) semiconductor material with a binding energy of 60 meV. It makes more attention to the ultraviolet (UV) optoelectronic devices. Up to now, the visible emission and ultraviolet lasing emission of ZnO have been the subject of much research. Although many groups put forward different mechanism of visible luminescence from ZnO, a suitable mechanism is very difficult to establish. Of course, to carry out ultraviolet lasing emission is what one expects to do. In order to study these two questions, high quality nanocrystalline ZnO thin films were prepared by thermal oxidation of ZnS thin films, which were deposited by using low pressure metalorganic chemical vapor deposition technique. The X-ray diffraction patterns and Raman spectra indicated that ZnS fully transformed into ZnO with a polycrystalline hexagonal wurtzite structure when ZnS thin films were oxidized at annealing temperature of above 700 oC in an oxygen ambient. The photoluminescence (PL) spectra of the ZnO thin films showed that the strongest ultraviolet photoluminescence (PL) at 380 nm was observed at annealing temperature of 900 oC, while the visible photoluminescence was barely observed. The effect of annealing temperature on its photoluminescence was discussed in detail in this thesis. The ultraviolet emission with a low energy tail resulted from the overlapping of free exciton emission and bound exciton emission. We use the laser output (320 nm, 200 fs) of Optical Parametric Amplifier (OPA) in an active passive mode-locked femtosecond Ti-Sapphire laser operating at a repetition rate of 1kHz as a exciting resource to develop optically pumped stimulated emission of ZnO thin films. When rectangular stripe laser irradiates thin films, optical resonant cavity is naturally formed between two nanocrystallites along with the rectangular laser stripe and planar weveguide confines the light scattering. We observed the ultraviolet stimulated emission of nanocrystalline ZnO thin films on SiO2 substrate. In the discussion of visible luminescence mechanism, in order to prove that the oxygen vacancies or defects distribute on the surface of nanocrystallites, we presented to prepare the ZnO thin films with doped Mn and studied the photoluminescence of ZnO:Mn. Together with luminescence spectra, X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonant (EPR), core-shell structure of nanocrystalline ZnO was put forward. In this thesis, we put forward that Vo** and [Vo*, electron] or [Vo**, two electrons] complex are luminescent centers of visible luninescnece. Passivation on the surface of nanocrystalline ZnO was responsible for an energy potential high enough to prevent surface states trapping the electrons or holes photogenerated, it should block the pathway to form the luminescence centers as the Vo** and [Vo*, electron] or [Vo**, two electrons] complex. A new visible luminescence mechanism was presented.
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