【作者】 王征；

【导师】 叶志镇； 何海平；

【作者基本信息】 浙江大学 ， 材料物理与化学， 2017， 博士

【摘要】 作为一种Ⅱ-Ⅵ族氧化物半导体材料,ZnO室温条件下禁带宽度3.37eV,激子束缚能为60meV,具有优异的发光性能,在LED和LD等光电器件领域具有极大的应用前景。二维的量子阱结构作为有源层,可实现对载流子的有效限制,是提高ZnO发光效率的关键。ZnO/ZnMgO量子阱中的发光行为,特别是激子复合行为及其对极性的依赖性等还有很多值得深入研究的地方。此外,随着以石墨烯为代表的新型二维材料的发现和相关新型光电器件的提出,制备自支撑的二维超薄ZnO材料,能使其具有独特的性质,并拓展其应用。本文主要研究二维ZnO材料,阐明二维结构中ZnO的激子复合机制,并探索新型二维ZnO材料,重点研究二维超薄ZnO和ZnO/ZnMgO量子阱的发光性能,主要包括以下内容:1.利用变温稳态和瞬态发光光谱详细研究了脉冲激光沉积法(PLD)生长的高质量Si基ZnO/Zn0.9Mg0.1O多量子阱中的激子复合行为。发现激子辐射复合寿命在19-300K范围内均随温度呈线性增加,证实其纯二维激子特征,表明直至室温,激子均被限制在量子阱内,没有热离化为三维激子。得到室温下的辐射复合速率0.87ns-1,高于现有文献报道值,表明量子阱的晶体质量很高,且具有本征的高效发光特性。另外,内建电场的存在导致了量子限域斯塔克效应(QCSE),使电子和空穴的波函数在空间上分离,导致PL发光峰的红移。2.系统研究了极性对分子束外延法(MBE)生长的ZnO/ZnMgO多量子阱激子复合特性的影响。发现极性和非极性量子阱中激子非辐射复合的主导过程有所不同,非极性量子阱中均由非辐射复合中心缺陷主导,而没有激子的去局域化和激子分解过程;非极性ZnO/ZnMgO多量子阱发光峰显著展宽且出现反常温度依赖特性,表明其中激子具有强局域化特性且局域态能级分布很宽;在高密度激发下,非极性量子阱的发光性质也有别于极性量子阱,其激子-激子散射发光出现阈值相对更低。3.利用水热法,分别以ZnS和ZnSe纳米片为中间产物,通过热氧化成功制备厚度约为2-5 nm,横向尺寸达到微米级的自支撑二维超薄ZnO。发现热氧化过程不仅可以得到ZnO,去除残留的有机物,且不破坏结构完整性。系统研究了水热生长温度、生长时间、热氧化温度等主要实验参数对二维超薄ZnO结构、形貌和发光性能的影响,并获得了最优参数。4.利用变温稳态和瞬态发光光谱研究了二维超薄ZnO的光生载流子复合特性,发现一些与ZnO体材料不同的新性质。发现低温下带边发光由自由激子的第一和第二声子伴线主导,其发光复合几率与激子动能的相关度特征参数显著低于体材料;深能级发光的辐射复合寿命具有零维特征,且陷阱态的存在使非辐射复合速率随温度的变化偏离常规理论预测;变温PL谱在160-250 K温度范围内出现负温度淬灭现象,光生载流子从陷阱态的去局域化导致室温内量子效率的提高,约为30%。5.初步探索了二维超薄ZnO作为紫外激发荧光粉的潜在应用。将发绿光的二维超薄ZnO样品与红光荧光粉和蓝光量子点混合,通过优化组分比例成功制备白光荧光粉,在390nm的紫外LED激发下获得较高质量的白光发光,CIE指数为(0.329,0.332)。更多还原

【Abstract】 As II-VI oxide semiconductor with bandgap of 3.3 7 eV and exciton binding energy of 60 meV at room temperature,ZnO has been considered as a promising material for potential application in optoelectronic devices due to its unique optical properties.As active layer,2D quantum wells structure can realize the effective control of carriers,which is the key to improve the luminescence efficiency of ZnO.There are numerous issues in the luminescence behavior of ZnO/ZnMgO quantum wells that worth further investigation,especially the behavior of exciton recombination and its dependence on the polarity.In addition,with the discovery of novel 2D materials like graphene and the invention of related novel optoelectronic devices,the fabrication of free-standing 2D ZnO will bring unique optoelectronic properties and extended applications to ZnO.In this thesis,we mainly focus on 2D ZnO materials,while illuminating recombination dynamics of excitons in 2D ZnO and exploring novel 2D ZnO materials.The details are as follows:1.The behavior of exciton recombination in Si-based ZnO/Zn0.9Mgi.0O multiple quantum wells grown by PLD was investigated detailly via temperature-dependence steady-state and time-resolved photoluminescence.There is a linear increase in the radiative decay time between 19 and 300 K,which is the characteristic feature for pure 2D excitons.The excitons are effectively confined in the quantum wells and do not thermalize to 3D excitons till room temperature.The radiative decay rate at 300 K is 0.87 ns-1,which is higher than those reported in the literatures,indicating the high quality and intrinsic high-efficiency luminescence characteristic of the quantum wells.In addition,the absence of internal electric field leading to QCSE,results in the spatially separated wavefunctions and increasing in PL lifetime.2.The influence of polarity on the exciton recombination in ZnO/ZnMgO multiple quantum wells grown by MBE has been investigated systematically.The dominant processes of non-radiative recombination of excitons in polar and non-polar quantum wells are different.For non-polar ZnO/ZnMgO quantum wells,the non-radiative recombination of excitons is dominated by non-radiative recombination centre defects,without delocalization and decomposition of exciton;the significant broadening and abnormal temperature-dependence characteristic indicate the strong localization of exciton while board distribution of localized states;under high excitation density,the luminescence property of non-polar ZnO/ZnMgO quantum wells is different from that of polar ZnO/ZnMgO quantum wells,while the P-band threshold of non-polar ZnO/ZnMgO quantum wells is lower than that of polar ZnO/ZnMgO quantum wells.3.Free-standing atomically thin ZnO layers were successfully synthesized via oxidizing hydrothermally grown ultrathin zinc chalcogenides layers.The lateral size of ZnO ultrathin layers is several micrometers,and the thickness is determined to be as thin as-2 nm.The thermal treatment process can help to remove the organic groups and to get atomically thin ZnO layers without damageing the structure integrity.The main experimental parameters including hydrothermal growth temperature,hydrothermal growth time and thermal treatment temperature have been investigated systematically to obtain the optimal parameters.4.The recombination behavior of photogenerated carriers in ZnO ultrathin layers was investigated via temperature-dependence steady-state and time-resolved photoluminescence.Some novel properties that different from that of ZnO bulk materials have been found.At low temperature,the LO-replicas of free exciton dominate the NBE emission,in which the dependence of the emission probability on the exciton kinetic energy is much smaller than that of bulk ZnO.The radiative recombination rate of deep-level luminescence has zero-dimensional feature.The negative thermal quenching behavior in the temperature range of 160-250 K indicates a detrapping/delocalization of photogenerated carriers,resulting in high internal quantum efficiency of-30%at room temperature.5.The potential application of ZnO ultrathin layers as UV-excited phosphor has been preminarily explored.By optimizing the composition proportion,the mixing of layered ZnO sample with red phosphor and blue quantum dot can form white emission phosphor.High quality white emission under 390 nm UV LED excitation has been obtained,with CIE coordinates of(0.329,0.332).更多还原