【作者】 石市委；

【导师】 孙兆奇；

【作者基本信息】 安徽大学 ， 物理电子学， 2014， 博士

【摘要】 氧化锌(ZnO)具有优异的光电性能,在紫外蓝光光电子器件、透明电子器件、自旋电子器件和压电及热电传感器等领域有着重要的研究价值,目前已成为学术界研究的一个焦点。虽然对氧化锌的研究已经有了相当长的历史,但ZnO材料的一些光学电学性能及其调控机理并未完全清楚,这些问题包括p型ZnO问题、ZnO的施主受主缺陷的辨认问题、ZnO在可见光区的发光中心问题及ZnO分级结构的可控制备问题等等。寻找这些问题的答案对于增强、扩展ZnO材料在器件上的应用以及器件功能的实用化来说至关重要。鉴于此,本论文主要在以下几个方面做了一些工作：(一)采用磁控溅射法制备了Mo掺杂的氧化锌(MZO)薄膜,研究了不同的掺杂量对ZnO薄膜的微结构、电学、光学及发光性能的影响,研究了退火对薄膜导电性能、发光性能的影响。结果表明,MZO薄膜为多晶颗粒膜,掺钼影响薄膜的表面粗糙度；退火后薄膜的多晶颗粒尺寸变大数倍。MZO’薄膜均为六方纤锌矿结构,且沿c轴择优生长。MZO薄膜的平均晶粒尺寸及薄膜内的应力均呈现随Mo掺杂量的增大而先增大后减小的趋势,MZO：2%薄膜具有最大的平均晶粒尺寸和内应力。退火可以使MZO薄膜的晶粒尺寸明显增大,同时使薄膜中的应力释放。XPS结果显示Mo在ZnO薄膜中呈+6价,显示Mo6+原子在溅射过程中其自身的化合态保持不变。MZO：2%薄膜的Zn2p3/2结合能峰中出现位于1022.0eV的子峰(对应于Zni),说明适量Mo掺杂可以促进Zni原子的生成。Mo掺杂对薄膜的光学透过率和光学带隙影响不大。MZO薄膜的电阻率随Mo掺杂量的增大呈先减小后增大的趋势,说明适量Mo掺杂可以降低MZO薄膜的电阻率。这应该归因于少量的钼掺杂刺激了Zni缺陷或Zni-X复合缺陷的生成,使薄膜中的Zni缺陷浓度增大,从而使载流子浓度增大。退火导致薄膜的电阻率急剧增大。这应该是由于薄膜中Zni缺陷浓度的降低和薄膜表面的氧吸附这两方面的原因导致的。未退火的MZO薄膜的光致发光谱中存在一个极弱的位于380nm处的ZnO本征发光峰和一个稍强的蓝光发光峰。退火使薄膜的光致发光强度快速增强,这应该是由于退火导致薄膜晶粒尺寸增大所导致的。退火还导致位于380和412nm位置处的发光峰逐渐被增强的位于400nm处的发光峰所掩盖,在525nm位置处也逐渐出现另一个新生成的绿光发光峰。在800℃下退火1小时后,MZO薄膜光致发光谱的发光峰位置基本一致,但MZO薄膜的发光强度几乎是未掺杂ZnO薄膜的发光强度的近10倍,说明在退火过程中MZO薄膜更容易生成发光缺陷(Vzn和Ozn缺陷)。(二)采用水热法分别制备了掺铝、掺镧和掺钇的ZnO纳米结构薄膜,并研究了每种样品的微结构、光学特性及低温发光特性。结果表明,掺铝氧化锌(AZO)纳米结构薄膜由六方纤锌矿结构的ZnO纳米锥构成,掺铝对薄膜的表面形貌和光学透过率没有明显影响。薄膜的光致发光谱存在两个比较宽的发光峰,P1峰和P2峰。随着掺杂量的增大,P1峰的绝对光强度及其对P2峰的相对光强度都迅速增大,并在掺杂浓度达到10%时达到最大值。在10-297K温度下的低温光致发光谱显示,P1峰受温度变化产生的改变不明显,但P2峰的发光强度随温度的升高呈现快速的淬灭。这种温度淬灭应该是由于当温度升高时,发光中心的晶格弛豫增强,无辐射跃迁几率增大,从而使发光效率降低所导致的。对于掺镧氧化锌(LZO)纳米结构薄膜,随着镧掺杂量的增大,ZnO纳米锥的平均直径和薄膜的(002)衍射峰的强度均增大。在紫光到绿光范围内,LZO薄膜的透过率比AZO薄膜的明显低很多。LZO薄膜在室温下紫外发光很弱,而在500-800nm内的可见光发光很强。随着镧掺杂量的增大,可见光区发光峰的强度也在逐渐增大,当掺杂浓度达到8%时,样品发光峰的强度是未掺杂ZnO薄膜的2.5倍左右。紫外发光峰强度随着掺杂量的增大没有明显变化。LZO薄膜的可见光区发光也呈现与AZO薄膜类似的温度淬灭现象,同时其紫外发光峰的峰位在升温过程中有红移现象,这种峰位的移动应该是由于温度升高时晶格常数增大所导致的。掺钇氧化锌(YZO)薄膜的微结构及光学透过率对不同钇掺杂量的变化情况与LZO薄膜的类似。室温下YZO薄膜在500-800nm范围内有较强的光致发光,但钇掺杂对发光谱的强度和峰位无明显影响,这一特点与AZO、YZO薄膜均不同。(三)采用化学浴沉积法在ZnO薄膜表面沉积了不同尺寸和密度的CdS量子点,研究了CdS-ZnO纳米异质结构薄膜的微结构、光学、光催化特性,具体结果如下。在ZnO表面,CdS量子点的尺寸和密度随着化学浴沉积次数的增大而越来越大；沉积4次得到的CdS-ZnO-4Ts样品表面的CdS量子点粒径均匀,分布较密。CdS量子点修饰导致薄膜吸收系数增大很多。CdS量子点修饰对ZnO发光的影响不明显。CdS-ZnO-4Ts薄膜在120分钟内对甲基橙溶液的降解率可达到96%,而纯的ZnO薄膜在120分钟的时间内只降解了35%的甲基橙,说明CdS量子点修饰可以明显增强ZnO薄膜的光催化效果。(四)采用电沉积法和阳极氧化法制备了ZnO纳米结构,具体结果如下。采用电沉积法制备的ZnO纳米结构呈现对电解液较为敏感的变化,当溶剂中的乙醇和水的比例为1：3时,为简单纳米片结构；当此比例为1：1时,制备出由纳米片一级一级生长所构成的“米”字形纳米分级结构；当此比例为3：1时,分级结构呈类似“雪花状”结构。电解液中所含乙醇比例越大,所得样品光致发光谱中红光区域的强度越小,蓝光区域的强度越大。采用阳极氧化法制备的ZnO多孔膜的表面形貌呈现随氧化电压的增大而改变的规律。当氧化电压为20V时,可制备出一种类似四方形管的突起状结构,这种结构的成因尚在进一步研究中。更多还原

【Abstract】 Owing to its excellent opto-electronic properties, ZnO has some important applications in optoelectronic devices, transparent electronics, spintronic devices, piezo electric devices, thermoelectric sensor, etc. It has gradually become a study focus in Ⅱ-Ⅵ semiconductor. Although ZnO has been studied for a long time, some issues of its properties and the regulation of its microstructure and performance are not fully understood. These issues include the preparation of p-type ZnO semiconductor, the identification of the donor and accept defects for the instinctive defects of ZnO, the origins of the emissions in the visible region and the controllable synthesis of ZnO nano-hierarchical structure. The comprehension of these issues will enhance and extend the application of ZnO materials in functional devices and facilitate the practicality of the ZnO-based devices. For this reason, we give attention to ZnO and have carried out many researches about a few of the above issues. The research works and main conclusions are described as follows.(1) The molybdenum doped ZnO (MZO) films were deposited by radio frequency magnetron sputtering. The MZO films are composed of polycrystalline grains with the wurtzite structure. Mo-doping influences the grain size and roughness of the MZO films, and leads to a compressive stress in the MZO films. The grain size increases several times greater after the annealing process. XPS reveals that there is only Mo6+no Mo5+or Mo4+, in the MZO films. This indicates that the valence of Mo6+is not easily changed during the sputtering process. Mo doping introduces two effects on Zn2p3/2XPS spectra. One is the decrease of the binding energy of Zn2p3/2electron, the other is the emergence of a smaller peak at1022.0eV (related to Zni)in Zn2p3/2XPS spectrum. This illustrates that Mo doping can promote the generation of the Zni defects. Mo doping has little effects on the transmittance and the optical bandgap of the MZO films. The resistance of the MZO films firstly increases then decreases with the increase of the Mo doping concentration. The resistivity of MZO films reaches the minimum when the Mo doping concentration is2wt.%. This means that doping suitable amount Mo atoms can reduce the resistance of the MZO films. It’s supposed that the proper Mo doping can stimulate the formation of the Zn; defects and prompt the conductivity of the MZO films. Annealing in air causes a significant increase in the resistivity of the MZO films, which can be attributed to the adsorption of oxygen atoms and the concentration change of the donor defects Zni and its complexes defects in the annealing process. There are one weak UV emission peak at380nm and one stronger blue emission peak in the photoluminescence (PL) spectra of the as-prepared MZO films. The PL spectral intensity of the annealed MZO films is much higher than that of the unannealed film. Such an enhancement should be induced by the increase of the grain size which affects the quantum efficiency of PL significantly. With the annealing temperature rising from600to800℃, the emission peaks located at380and412nm are covered by an emerging emission peak located at400rim, and a new emission peak located at525nm appeared. The spectral intensity of the annealed MZO films is about ten times higher than that of the annealed ZnO film, but the position of the emission peaks (at400and525nm) is almost the same. It’s supposed that in the annealing process Mo-doping benefits the forming of the Vzn and Ozn defects which are the origins of the emissions at400and525nm respectively.(Ⅱ) The Al doped, La doped and Y doped ZnO nanostructure films were prepared by the hydrothermal method. The Al doped ZnO (AZO) nanostructure films are constructed by the nanopyramids with the wurtzite structure. Al doping has. little effect on the surface morphology and the light transmittance of the AZO films. There are two broad emission peaks, a UV-violet emission peak (PI) and a green-red emission peak (P2), in the PL spectra of the AZO films. At room temperature, with the increase of the Al doping concentration, the intensity of the PI peak increased sharply and reached the maximum when the doping concentration is10%; the relative intensity among the components of the green-red emission peak also changed with the increase of the Al doping concentration. The temperature dependent PL spectra show that the P2peak quenched when the temperature rose from10to297K, but the PI peak almost doesn’t change with the increase of sample temperature. It’s supposed that the fluorescence quenching of the green-red emission peak is attributed to the increased probability of the nonradiative exciton recombination caused by the multiphonon emission. The La doped ZnO (LZO) films have the similar microstructure with the AZO films. The diameter of the LZO nanopyramids and the intensity of the (002) XRD diffraction peak of the LZO films increase with the increase of the La doping concentration. The transmittance of the LZO films is much smaller than that of the AZO films. At room temperature the UV emission of the LZO films is very weak, but the emissions in the range of500-800nm is very strong. With the increase of La doping concentration, the intensity of the emissions in the visible region increases and reaches the maximum when La doping concentration is8%. Doping has little effect on the UV emissions. When the sample temperature rising from10to294K, the emissions in the visible region quench quickly, and the UV emission peak appears red shift which should be attributed to the increase of the lattice constant. The Y doped ZnO (YZO) films have similar properties in microstructure and light transmittance. At room temperature the YZO films have strong emissions in the visible region, but Y doping has little effect on the PL spectral intensity and the emissions’peak position. This is different with that of the AZO or LZO films.(Ⅲ) The CdS quantum dots (CdS QDs) were deposited on the surface of the ZnO nanostructure films by chemical bath deposition. The size and the density increase with the increase of the deposition cycles. After four deposition cycles (this sample was marked as CdS-ZnO-4Ts), the CdS QDs have uniform size and large density. The CdS QDs lead to an increase of the absorption coefficient of the ZnO films, but have little effect on the PL spectra of the ZnO films. The sample CdS-ZnO-4Ts has a good photocatalytic performance, its degradation rate of methyl orange solution during120minutes reaches96%, while that of the pure ZnO films is just35%. This suggests that the surface modification of ZnO films by CdS QDs is benefit for its photocatalytic performance.(IV) The ZnO nanostructure films were synthesized by electro-deposition and anodic oxidation. In the electro-deposition process, the volume ratio of alcohol to deionized water in the electrolyte is an important factor in the growth process of ZnO nanostructure. The different ZnO nanostructures, that is, ZnO nanosheets,"*"-like ZnO nanostructures, snowflakes-like ZnO hierarchical structure were synthesized while the ratio is1:3,1:1and3:1, respectively. The higher the ratio is, the more complicated the nanostructures are. The PL spectra of these samples show that when the ratio become higher, the emission in red light region become weaker and the emission in blue light region become stronger. The porous ZnO films were prepared by anodic oxidation. Its surface morphology has certain relation with the anodizing voltage. When the anodizing voltage is20V, the nano-square-tubes were achieved. Its growth mechanism will be studied further.更多还原