基于宽禁带半导体量子点的高效蓝紫光发光二极管的研制和性能研究

The semiconductor quantum dot-based light-emitting diodes (LEDs) have now become the focus of intensive research. These LEDs possess the merits of high stability, high exernal quantum efficiency, pure light color, tunable emission wavelength, long lifetime, energy-saving, and small volume. Hence they have attracted great interest from both the scientific and the industrial communities. The LEDs based on the group II-VI semiconductor quantum dots are the most highly investigated currently; however, the cytotoxicity of the heavy metal ions contained in them greatly hampers their wide applications. In comparison, the group IV semiconductor quantum dots are much more biocompatible and abundant in the earth. Therefore, in this proposed project, we plan to study the LEDs majorly based on the SiC quantum dots. SiC is a wide bandgap semiconductor possessing a variety of excellent properties such as high thermal and chemical stabilities and radiation-resistance. Moreover, blue-violet emissions can readily be implemented by using the SiC quantum dots due to their wide bandgap according to quantum confinement effect. Hence the SiC quantum dots are perfect candidates of basic componnets for blue-violet emitting LEDs. We shall fabricate the SiC quantum dots by using the electrochemical method and then link them with surface organic molecules. Then by combining usage of electron and hole transporting layers of conducting polymers, the mutilayer LED structures with blue-violet light emission can be fabricated. Furthermore, the quasi-white light emitting LEDs can be constructed by concurrently using the blue-emitting SiC quantum dots and the red-yellow-emitting Si quantum dots. We shall intensively study the fruitful phenomena of energy transfer, carrier conduction, and electroluminescence mechanism in the multilayered structures of the fabricated LEDs. We shall study and exploit the methods of optimizing the performance of the LEDs.

半导体量子点发光二极管是当前国际上的研究热点。基于量子点的发光二极管稳定、高效、单色性好、颜色可调、寿命长、节能、体积小，已引起全球科研人员和工业界的高度关注。目前研究较多的是II-VI族化合物半导体量子点发光二极管，但重金属离子的毒性限制了其应用前景。相比之下，IV族半导体量子点生物相容性好且元素储量大。本申请中我们拟研究基于IV族宽禁带半导体碳化硅量子点的发光二极管。碳化硅具有热稳定性和化学稳定性好、抗辐射等许多优点，并且由于量子限制效应很容易实现蓝紫光发射，因而是极具潜力的蓝紫光发光二极管材料。我们利用电化学方法制备碳化硅量子点，并对其进行表面处理，结合能传导载流子的导电聚合物实现多层结构的具有蓝紫光发射的发光二极管，同时结合具有红黄光发射的硅量子点可实现混合量子点准白光发光二极管。重点研究各结构中的能量转移机制、载流子传导机制以及电致发光机制等，探索优化量子点发光二极管性能的方法。

碳化硅等IV族量子点因具有优异的物理性能并且绿色环保，同时其发光波长可覆盖可见光和近紫外光区域，所以有望作为可见/近紫外和准白光光源而在固态光显示和照明领域发挥重要作用，已引起国内外很大研究兴趣。我们在碳化硅和C8等IV族量子点以及CuInS2、ZnO等其它纳米晶体的制备、发光机制以及电致发光等方面开展研究并取得一批具有重要科学意义和应用前景的成果。.制得基于宽禁带C8碳量子点的无机–有机电致发光器件。发现随偏压增加在量子点/有机物界面处的势垒降低导致载流子从量子遂穿变为直接注入，引起复合发光区域从有机物层转移到量子点层，从而导致电致发光波长可随偏压改变而在蓝光和红光之间切换。制备出基于碳化硅量子点的电致发光器件，无载流子传输层的器件表现出准白光发射，有载流子传输层的器件表现出蓝–绿色电致发光，对其载流子传输和电致发光机制进行了深入研究。这些电致发光器件的研究表明IV族量子点在固体发光领域具有良好应用前景。研究发现碳化硅纳米团簇具有5.1 eV间接带隙，表现出两种氧表面缺陷发光。发现碳化硅纳米颗粒的带隙值与直径的0.97次方成反比。发现与C=O相关的表面态是产生碳化硅量子点蓝光发射的根源。发现在常温常压和超声波作用下，碳化硅纳米晶体能发生从α到β相的转变。研究了碳化硅和氧化锌等量子点间的光再吸收，建立理论模型很好地解释了实验现象，发现利用金属表面等离激元聚光效应可消弱光再吸收。这些结果对基于量子点的固体发光器件的研制很有意义。发现氧化锌量子点中的绿光来源于导带到深能级缺陷跃迁。发现界面阳离子交换引起CuInS2/ZnS到CuxZn1−xInS2/ZnS:Cu量子点的结构转变，并且后者发光峰反常蓝移，研究表明其绿光和橙光发射分别起源于内核和壳层的缺陷。研究了一维氧化锌纳米晶体生长过程，发现在晶体生长过程中发生了轴向和测向oriented attachment (OA)，计算表明由自发极化力驱动的轴向OA主导了氧化锌纳米晶体的生长。这些结果提高了我们对于溶液中晶体生长机制的认识。