钙钛矿半导体中的瞬态物理过程研究

发布时间：2018-01-10 16:48

本文关键词：钙钛矿半导体中的瞬态物理过程研究　出处：《南京大学》2016年博士论文　论文类型：学位论文

【摘要】：近年来,一类具有钙钛矿晶体结构的金属卤化物半导体材料横空出世,在光电转换器件方面取得了非同一般的表现,与器件进展相比,钙钛矿半导体材料的光电物理机制的认识还很不深入。在有限的研究报道中,学界发现钙钛矿半导体带间缺陷少,载流子扩散距离长,这些特点使得钙钛矿半导体的发光效率也很好,可能应用于发光二极管和激光器等方面。钙钛矿半导体使人们首次意识到,卤(Ⅶ)族化合物也可能存在极好的光电半导体材料,然而相比较Ⅳ族,Ⅲ-Ⅴ族,Ⅱ-Ⅵ族等半导体材料,它的电子,声子,自旋等基本物理性质研究极少。本论文面向钙钛矿半导体材料的光电器件应用,利用超快光谱学方法,探究不同的时间尺度的激子动力学、自旋动力学以及热动力学等物理过程,并得到如下一系列研究结果：1、利用钙钛矿半导体CsPbBr3量子点实现了低阈值稳定的双光子激发激光发射。我们z扫描实验发现CsPbBr3量子点具有高效的双光子吸收(吸收截面约为2.7×106GM),并利用超快瞬态吸收谱的研究方法探讨了双光子激发下CsPbBr3量子点中光生载流子的动力学,观察到光学增益建立过程,并明确指出多激子效应对光学增益产生的贡献；在低功率的双光子激发下,我们在CsPbBr3量子点薄膜中实现自发辐射放大,其净增益系数高达580cm-1；进一步,将双光子激发的光学增益耦合到回音壁模式微腔中,成功实现了双光子激发的CsPbBr3量子点激光器,激发阈值非常低(＜1 mJ/cm2),稳定性很高(107 shots).2、在低温强磁场条件下(0-10 T),我们研究了钙钛矿半导体材料的磁光效应。我们发现有机、无机杂化钙钛矿半导体CH3NH3PbI3薄膜中外磁场诱导的圆偏振发光现象,并将此现象归结为CH3NH3PbI3的激子中电子和空穴g因子相差较大(g因子的差值△g～0.38)；通过对比实验,发现CH3NH3PbI3薄膜中缺陷态对其带隙发光的磁致圆偏振影响很小；进一步实验发现,随着载流子浓度的逐渐升高,其磁致圆偏振度逐渐减小,时间分辨荧光光谱的也提示磁致圆偏振度随激子浓度动态演化,并提出激子的多体效应是诱发上述现象产生的原因。3、稳定性是钙钛矿半导体光电器件面临的最主要挑战,材料的散热被认为是稳定性差的主要原因之一,我们利用时域热反射谱的实验技术手段测量了致密MAPbI3薄膜的室温热导率约为11.2Wm-1k-1,该热导率可以与其他常用半导体光电材料可比拟。初步阐明了钙钛矿半导体MAPbI3本身的导热性能并不是导致器件散热差的主要原因。随后通过温度依赖的实验,得到了从低温4K到高温370K这个区间MAPbI3薄膜的热导率,并通过分析得到材料中的有机阳离子和其结构相变是引起热导率变化的重要原因；温度依赖的光致发光谱和拉曼光谱进一步阐明了MAPbI3的结构相变对其热导率产生的影响。
[Abstract]:In recent years, a kind of metal halide turned semiconductor material having a perovskite crystal structure was born, in the photoelectric converter has achieved extraordinary performance, compared with the progress in understanding the physical mechanism of optoelectronic devices, the perovskite semiconductor materials are not in-depth. In the limited research reports, researchers discovered that the perovskite semiconductor intersubband less defects, carrier diffusion distance is long, these features make the luminous efficiency of perovskite semiconductor is also very good, may be applied to the light emitting diode and laser etc.. To make people aware of perovskite semiconductor for the first time, (VII) halogen compounds may also have excellent optoelectronic semiconductor materials, however, compared to group IV, III-V. II-VI semiconductor material, its electron phonon, study on the basic physical properties of spin photodevice. Rarely used this paper oriented perovskite semiconductor materials, the use of Ultrafast spectroscopy method on different time scales of exciton dynamics, spin dynamics and thermodynamic processes, and obtain the following a series of research results: 1, the perovskite CsPbBr3 semiconductor quantum dots to achieve two-photon excitation stable low threshold laser. We found Z scanning experiments of CsPbBr3 quantum dots with efficient two-photon absorption (the absorption cross section is about 2.7 * 106GM), the research methods and the use of ultrafast transient absorption spectra of two photon excitation dynamics of photogenerated carriers of CsPbBr3 quantum dot, observed the establishment process of optical gain, and pointed out that the multi exciton effects on the optical gain with low power; in the two-photon excitation we realize, the amplified spontaneous emission in CsPbBr3 quantum dots in the films, the net gain coefficient is as high as 580cm-1; further, the optical gain of two photon excitation coupling To the whispering gallery microcavity, the successful implementation of the CsPbBr3 quantum dots excited by two-photon laser excitation threshold is very low (< 1 mJ/cm2), high stability (107 shots).2, at low temperature under a high magnetic field (0-10 T), we studied the magneto-optical effect of perovskite semiconductor materials. We found that organic inorganic hybrid perovskite CH3NH3PbI3 semiconductor thin film, magnetic field induced luminescence and circular polarization phenomenon, and this phenomenon is attributed to the electron and hole CH3NH3PbI3 exciton g factor in large difference (difference delta g factor G ~ 0.38); through the comparative experiment, found that the defects of CH3NH3PbI3 films on the band gap luminescence effect of magnetic circular polarization very small; further experiments showed that when increasing the carrier concentration, the magnetic circular polarization decreases, time-resolved fluorescence spectra also indicate that with the dynamic evolution of the exciton magnetic circular polarization, and The many body effect is the.3 cause of exciton induced by the above phenomenon, the stability is the main challenge of perovskite semiconductor optoelectronic devices, material cooling is considered to be one of the main reasons of poor stability, we use the time-domain heat reflection spectra of the experimental techniques of dense MAPbI3 film measuring thermal conductivity at room temperature is about 11.2Wm-1k-1. The thermal conductivity can be used with other semiconductor optoelectronic materials can be compared. Preliminary clarify the thermal conductivity of semiconductor MAPbI3 perovskite itself is not the main cause of poor heat dissipation. The device followed by a temperature dependent experiment, thermal conductivity from low temperature to high temperature 4K 370K MAPbI3 this interval rate of the film is obtained, and through the analysis of organic cationic materials and the structural transition is an important cause of thermal conductivity change; temperature dependent photoluminescence spectra and Raman spectroscopy to further clarify The effect of the structural phase transition of MAPbI3 on its thermal conductivity is investigated.

【学位授予单位】：南京大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O471

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