【作者】 杨丹；

【导师】 王登魁；

【作者基本信息】 长春理工大学 ， 电子科学与技术， 2023， 硕士

【摘要】 铅基硫族化合物量子点是直接带隙半导体材料,具有高荧光量子产率、大激子波尔半径,宽波长调谐范围以及高效的单光子多激子效应等特点而被广泛研究。然而将铅基硫族化合物量子点从湿化学合成扩展至高性能光电子器件应用仍然存在较大困难,这是因为铅基硫族化合量子点表面原子活性较高,易被氧化掺杂,造成量子点光电特性发生不可控的变化。另一方面,铅基硫族化合物量子点表面的悬挂键以及长链配体导致载流子传输困难,使制备的光电子器件性能不佳。因此,本文采用湿化学方法合成PbS、PbSe量子点,并通过核壳结构与TBAI配体改善量子点的发光稳定性差与载流子传输问题,具体研究内容包括以下两个部分:(1)通过控制量子点的生长时间,合成了发光峰为1330 nm、1420 nm以及1500 nm的PbS量子点,通过透射电子显微镜(TEM)、X射线衍射(XRD)、红外吸收(Abs)和光致发光光谱(PL)测试,表明合成的量子点质量较好。对三种量子点进行变温变功率光谱测试,发现发光峰在1330 nm和1420 nm的量子点存在载流子的热激活过程。为了提升PbS量子点的稳定性,通过阳离子交换法合成了不同壳层厚度的PbS/CdS量子点,极大的改善了PbS量子点的发光稳定性,但引入的壳层结构又使量子点的发光强度降低,这是由于壳层结构引入了新的缺陷态。最后研究了TBAI配体对量子点光电特性的影响,使用PbS-TBAI量子点制备的光电探测器的响应速度相比没有配体交换的量子点提高了81%,达到了1.45 s。(2)合成了一系列不同发光波段的PbSe量子点,并对发光波段为1767 nm、1975 nm和2004 nm的量子点进行变温变功率光谱测试,发光峰为1767 nm的量子点暴露在空气中氧化一段时间后,发光强度随温度升高而降低。未经氧化的1975 nm与2004 nm量子点发光强度随温度升高而增加。生长PbSe/CdSe结构用来改善PbSe核层的发光稳定性,CdSe壳层的引入钝化了量子点表面原有的缺陷,使其PL光谱由在高能端存在较长带尾的形状变为对称的高斯波形,但CdSe的包覆造成了发光强度降低。将PbSe、PbSe/CdSe量子点应用于光电探测器中,使用TBAI配体减小量子点间距,PbSe/CdSe-TBAI量子点光电探测器响应速度最快,这是因为CdSe可能改善了量子点因氧化产生的陷阱态。本文实现了从铅基硫族化合物量子点制备到光电子器件的应用,通过温度功率相关的PL光谱研究了载流子的动力学过程,采用阳离子交换合成核壳结构极大的改善了量子点的发光稳定性,并利用TBAI配体交换减小了量子点间距,提升载流子传输特性,为实现高性能的红外光电子器件奠定基础。更多还原

【Abstract】 Lead chalcogenide quantum dots are direct bandgap semiconductor materials and they have been extensively investigated due to excellent properties of high fluorescence quantum yields,large exciton Bohr radius,wide wavelength tuning range and efficient multi-exciton emission.However,it is still difficult to extend the lead chalcogenide quantum dots from wet chemical synthesis to the application of high-performance optoelectronic devices.This is because the surface atomic activity of the lead chalcogenide quantum dots is high,which is easy to be oxidized and doped,resulting in uncontrollable changes in the photoelectric properties of quantum dots.On the other hand,the dangling bond defects and long chain ligands on the surface of lead chalcogenide quantum dots lead to the difficulty of carrier transport,which will prompt the poor performance of optoelectronic devices.Therefore,PbS and PbSe quantum dots are synthesized in this paper.The problems of poor luminescent stability and carrier transport are improved through core-shell structure and TBAI ligand.The specific contents and related results are as follows:(1)By adjusting the growth time of quantum dots,PbS quantum dots with peaks located at 1330 nm,1420 nm and 1500 nm were synthesized.The results of transmission electron microscopy(TEM),X-ray diffraction(XRD),infrared absorption(Abs),and photoluminescence spectroscopy(PL)showed that the quality of the synthesized quantum dots was good.The thermal activation process of carriers in PbS quantum dots with emission peaks located at 1330 nm and 1420 nm was observed through the temperature-and power-dependent PL spectra.In order to improve the stability of PbS quantum dots,PbS/CdS quantum dots with different shell thicknesses were synthesized by cation exchange,which greatly improved the luminescent stability of PbS quantum dots.But the CdS shell structure also reduced the luminescent intensity of quantum dots,which is due to the introduction of new defect states in PbS quantum dot.Finally,the influence of TBAI ligand on the photoelectric properties of quantum dots is studied.The photodetector fabricated with PbS-TBAI quantum dots has the fastest response speed,reaching 1.45 seconds,which is 81 % higher than that of quantum dots without ligand exchange.(2)A series of PbSe quantum dots with different PL peaks position were synthesized.And the peaks for PbSe quantum dots located at 1767 nm,1975 nm and2004 nm were measured by temperature-and power-dependent PL spectra.The results showed that quantum dots with peaks located at 1767 nm were exposed to air for a period of time,and the luminescent intensity decreased with the increase of temperature.The intensity of the PL for unoxidized quantum dots of peaks located at1975 nm and 2004 nm increased with the increase of temperature.PbSe/CdSe quantum dots structure was used to improve the luminescent stability of the PbSe core quantum dots.The CdSe shell passivated the original defects on the surface of PbSe quantum dots,making its PL spectrum change from a shape with a long tail at the high energy end to a symmetric Gaussian waveform,but the new defects caused the decrease of the luminescent intensity.PbSe,PbSe/CdSe quantum dots were applied to fabricated photodetectors,and TBAI ligand was used to reduce the spacing of quantum dots.PbSe/CdSe-TBAI quantum dot photodetectors have the fastest response speed,this is because CdSe may improve the trap-state of quantum dots due to oxidation.In this paper,the synthesis of lead chalcogenide quantum dots and the fabrication of optoelectronic devices have been realized.The dynamics of carriers have been studied by temperature-and power-dependent PL spectra.The core-shell structures synthesized by cation exchange have greatly improved the luminescent stability of quantum dots.TBAI ligand has reduced the spacing of quantum dots and improved the transmission of carriers.This paper laid the foundation for the realization of high-performance infrared optoelectronic devices.更多还原