脉冲激光沉积制备ZnO基量子阱及其光学性质研究
发布时间：2018-10-19 10:54
【摘要】：作为一种宽带隙Ⅱ-Ⅵ族氧化物半导体,ZnO被认为是光电子产业的一种有希望的候选材料,在蓝光/紫外(UV)波段有着广阔的应用前景。因为激子结合能高达60 meV,ZnO的吸引力主要表现在激子室温稳定性方面,这对于半导体器件,如发光二极管(LEDs)、二极管激光器、紫外探测器等的应用均具有十分重要的意义。例如,人们预测ZnO中激子复合产生的激射甚至可以出现在室温以上。在设计和制作光电子器件的进程中,需要制备高质量的ZnO基异质结和量子阱结构,因为量子限域效应可以有效提高器件的发光效率。本博士论文以ZnO基多量子阱(MQWs)为中心,主要探讨了ZnO基MQWs的制备、结构和光学性质,涉及光致荧光(PL)、量子限域效应以及热稳定性。主要研究成果总结如下：(1)通过优化ZnO和ZnMgO单层膜在c轴蓝宝石基片上的生长条件,利用脉冲激光沉积(PLD)方法成功地制备出了具有明确多层结构的10个周期的ZnO/ZnMgO多量子阱。量子阱的阱层厚度在1.4到3.0 nm之间变化。在325 nm的He-Cd激光激发下,所有的量子阱样品在室温下均发射出强的紫外荧光。量子限域效应导致荧光光子的能量在3.38到3.52 eV之间变化。此外,在ZnO/ZnMgO量子阱的PL光谱中,首次观察到极度增强的多声子Raman散射(RRS)现象。光谱分析表明,增强的RRS可以归因于激发光和发射光与量子阱中ZnMgO垒层之间的能量共振,即入射共振和出射共振引起的多声子Raman散射的增强。另一方面,量子阱和ZnMgO单层膜中多声子Raman散射高度吻合,表明量子阱垒层与相同条件下生长的ZnMgO单层膜具有相同的成分,这可以看作是ZnO/ZnMgO量子阱具有明确多层结构的有力证据。利用ZnMgO单层膜的PL光谱及通过多声子RRS确定的纵光学声子的能量,估算出ZnMgO垒层中MgO的含量约为15%,进而计算出ZnO和ZnMgO之间导带和价带的偏移量分别为338和38 meV。在此基础上,根据Kronig-Penney模型计算的ZnO/ZnMgO量子阱中的PL位移随阱层厚度的变化与～12K下的实验光谱结果一致。此外,实验结果表明,ZnO/ZnMgO量子阱在退火温度低于600°C时是稳定的；当退火温度提升至700℃以上时,量子阱中ZnO/ZnMgO多层结构将被破坏。(2)作为荧光杀手,Co2+离子掺杂到ZnO中将导致激子复合荧光的淬灭,但荧光淬灭的物理机制是一个悬而未决的问题。在本工作中,首次利用ZnCoO/ZnMgO多量子阱样品系统研究了Co2+离子掺杂引起的荧光淬灭现象。ZnCoO/ZnMgO多量子阱利用脉冲激光沉积方法生长在带有～20 nm ZnO过渡层的c面蓝宝石基片上,并表现出与ZnO/ZnMgO多量子阱样品相似的多声子RRS增强现象,证明ZnCoO/ZnMgO多量子阱中多层膜结构足够好,以保证周期性量子阱的形成。与相同条件下生长的ZnCoO单层膜相比,量子限域效应导致ZnCoO/ZnMgO量子阱样品中位于～1.80 eV的Co2+离子荧光增强,即量子限域效应增强了高度局域化的Co2+3d电子能级的荧光发射。但是,激子复合的荧光淬灭现象在ZnCoO/ZnMgO量子阱样品中仍然存在。因此,Co2+离子掺杂引起的激子荧光淬灭可以确认为ZnO激子和局域化的Co2+3d电子态之间的能量转移,进而提出了荧光共振能量转移(FRET)是导致激子荧光淬灭和位于～1.80 eV的Co2+离子荧光增强的物理机制。(3)在PLD方法制备的具有高外延度的ZnO薄膜中,发现了一个异常的具有宽谱特征的光致荧光峰,位于近带边(NBE)区域,PL峰值在～3.0 eV附近。利用变温PL光谱、PL激发谱和时间分辨PL光谱,通过与退火样品和ZnO单晶样品的比较研究,这种异常的具有宽谱特征的NBE荧光发射不能简单地归因于某种特定的缺陷。为此,我们提出了一个带尾荧光模型。我们认为,ZnO薄膜中各种缺陷、化学无序和晶格应变可能会形成局域化的电子态,位于ZnO导带以下,形成能带带尾。这种异常的NBE荧光发射正是源于激子在能带带尾热弛豫过程中的辐射复合。这一物理机制被时间分辨光谱和变温光谱的定量拟合结果所证实。此外,发展了一种管式放电等离子体束流辅助的PLD装置,用于制备N掺杂ZnO薄膜,并研究了ZnO薄膜的电输运性质和光致荧光光谱随沉积过程中0分压的变化。
[Abstract]:As a wide band gap II-VI oxide semiconductor, ZnO is regarded as a promising candidate material for the optoelectronic industry, and has a wide application prospect in the blue/ ultraviolet (UV) wave band. Because the exciton binding energy is up to 60 meV, the attraction of ZnO is mainly manifested in the stability of exciton room temperature, which is very important for semiconductor devices such as light emitting diode (LED), diode laser, ultraviolet detector and so on. For example, it is predicted that the triplet state of exciton recombination in ZnO may even occur at room temperature or more. In the process of designing and fabricating optoelectronic devices, high quality ZnO-based heterojunction and quantum well structures need to be prepared because the quantum confinement effect can effectively improve the light-emitting efficiency of the device. The preparation, structure and optical properties of ZnO-based MQWs, including light-induced fluorescence (PL), quantum confinement field effect and thermal stability, are discussed. The main results are summarized as follows: (1) By optimizing the growth conditions of ZnO and ZnMgO single-layer films on c-axis sapphire substrate, a 10-cycle ZnO/ ZnMgO multi-quantum well with definite multi-layer structure was successfully fabricated by pulsed laser deposition (PLD) method. the well layer thickness of the quantum well varies between 1. 4 and 3. 0nm. All quantum well samples emit strong ultraviolet fluorescence at room temperature under the excitation of He-Cd laser at 325 nm. The quantum confinement effect causes the energy of the fluorescent photons to vary from 3.38 to 3.52 eV. In addition, in PL spectra of ZnO/ ZnMgO quantum wells, extremely enhanced multi-phonon Raman scattering (RRS) phenomenon was observed for the first time. The spectral analysis shows that the enhanced RRS can be attributed to the enhancement of the energy resonance between the excitation light and the emission light and the ZnMgO barrier layer in the quantum well, that is, the enhancement of the multi-phonon Raman scattering caused by incident resonance and emission resonance. On the other hand, the multi-phonon Raman scattering height in the quantum well and the ZnMgO single-layer film is consistent, which indicates that the quantum well barrier layer has the same composition as the ZnMgO single-layer film grown under the same conditions, which can be seen as a strong evidence that the ZnO/ ZnMgO quantum well has a definite multi-layer structure. The content of MgO in ZnMgO barrier layer is estimated to be about 15% by using PL spectrum of ZnMgO single layer film and the energy of longitudinal optical phonon determined by multi-phonon RRS, and then the offset of conduction band and valence band between ZnO and ZnMgO is calculated as 338 and 38meV, respectively. On this basis, the PL displacement in the ZnO/ ZnMgO quantum well calculated from the Kronig-Penney model is consistent with the experimental spectral results under ~ 12K. Furthermore, the experimental results show that the ZnO/ ZnMgO quantum well is stable when the annealing temperature is lower than 600 掳 C, and when the annealing temperature is raised above 700 鈩，
本文编号：2280906
[Abstract]:As a wide band gap II-VI oxide semiconductor, ZnO is regarded as a promising candidate material for the optoelectronic industry, and has a wide application prospect in the blue/ ultraviolet (UV) wave band. Because the exciton binding energy is up to 60 meV, the attraction of ZnO is mainly manifested in the stability of exciton room temperature, which is very important for semiconductor devices such as light emitting diode (LED), diode laser, ultraviolet detector and so on. For example, it is predicted that the triplet state of exciton recombination in ZnO may even occur at room temperature or more. In the process of designing and fabricating optoelectronic devices, high quality ZnO-based heterojunction and quantum well structures need to be prepared because the quantum confinement effect can effectively improve the light-emitting efficiency of the device. The preparation, structure and optical properties of ZnO-based MQWs, including light-induced fluorescence (PL), quantum confinement field effect and thermal stability, are discussed. The main results are summarized as follows: (1) By optimizing the growth conditions of ZnO and ZnMgO single-layer films on c-axis sapphire substrate, a 10-cycle ZnO/ ZnMgO multi-quantum well with definite multi-layer structure was successfully fabricated by pulsed laser deposition (PLD) method. the well layer thickness of the quantum well varies between 1. 4 and 3. 0nm. All quantum well samples emit strong ultraviolet fluorescence at room temperature under the excitation of He-Cd laser at 325 nm. The quantum confinement effect causes the energy of the fluorescent photons to vary from 3.38 to 3.52 eV. In addition, in PL spectra of ZnO/ ZnMgO quantum wells, extremely enhanced multi-phonon Raman scattering (RRS) phenomenon was observed for the first time. The spectral analysis shows that the enhanced RRS can be attributed to the enhancement of the energy resonance between the excitation light and the emission light and the ZnMgO barrier layer in the quantum well, that is, the enhancement of the multi-phonon Raman scattering caused by incident resonance and emission resonance. On the other hand, the multi-phonon Raman scattering height in the quantum well and the ZnMgO single-layer film is consistent, which indicates that the quantum well barrier layer has the same composition as the ZnMgO single-layer film grown under the same conditions, which can be seen as a strong evidence that the ZnO/ ZnMgO quantum well has a definite multi-layer structure. The content of MgO in ZnMgO barrier layer is estimated to be about 15% by using PL spectrum of ZnMgO single layer film and the energy of longitudinal optical phonon determined by multi-phonon RRS, and then the offset of conduction band and valence band between ZnO and ZnMgO is calculated as 338 and 38meV, respectively. On this basis, the PL displacement in the ZnO/ ZnMgO quantum well calculated from the Kronig-Penney model is consistent with the experimental spectral results under ~ 12K. Furthermore, the experimental results show that the ZnO/ ZnMgO quantum well is stable when the annealing temperature is lower than 600 掳 C, and when the annealing temperature is raised above 700 鈩，
本文编号：2280906
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