基于能带工程/应力调控的高效InGaN基红光LED的研究

High brightness InGaN-based blue LED has been widely used in optoelectronic devices, such as solid-state lighting and display. However, the fabrication of the high-efficiency InGaN-based red LED has been a problem that needs to be solved in this research field, due to the high volatility of In over InN and the poor miscibility between GaN and InN. The project will fabricate InGaN-based red LED by introducing InGaN/GaN quasi-superlattice underlying buffer layer as strain release layer, AlGaN interlayer with high aluminum content as strain High brightness InGaN-based blue LED has been widely used in optoelectronic devices, such as solid-state lighting and display. However, the fabrication of the high-efficiency InGaN-based red LED has been a problem that needs to be solved in this research field, due to the high volatility of In over InN and the poor miscibility between GaN and InN. The project will fabricate InGaN-based red LED on the base of conventional InGaN-based blue LED structure by using band engineering/strain control, that is, through introducing InGaN/GaN quasi-superlattice underlying buffer layer as strain release layer, AlGaN interlayer with high aluminum content as strain compensation layer and low temperature (LT) p-GaN buffer layer as hole injection layer (can also adjust band diagram) into the conventional InGaN-based blue LED structure to fabricate InGaN-based red LED. By a variety of spectra measurements (such as PL, EL, TRPL, etc.) and structure characterization (such as AFM、XRD、Raman、TEM, etc.), to investigate the effect of the structural parameters and growth process on the defect density, localization effect, quantum-confined Stark effect, radiation wavelength (In component incorporated rate) and PL efficiency. Based on the experimental results obtained in this project, we clarify the internal physical mechanisms of the carrier injection (production), transport and radiative recombination process, and eventually obtain the optimal structure parameters and growth process for fabricating high-efficiency InGaN-based red LED.

高亮度InGaN基蓝光LED已经被广泛地应用于照明和显示等领域。然而，由于In的易挥发性以及InN和GaN之间的低互溶度等原因，高效InGaN基红光LED的制备一直是该领域丞待解决的难题。本项目拟在传统InGaN基蓝光LED结构的基础上，通过能带工程/应力调控，即通过导入准超晶格InGaN/GaN下置层作为有源区应力释放层、AlGaN插入层作为阱/垒界面的应力补偿层、低温p-GaN缓冲层作为空穴注入层（兼具调整能带图形）来制备InGaN基红光LED。通过多种光谱测量（光致发光、电致发光、时间分辨等）和结构质量表征（AFM、XRD、Raman、TEM等），来调查结构参数和生长工艺对缺陷密度、应力、辐射波长（In并入率）和发光效率等的影响规律，从而阐明载流子的注入（产生）、传输、复合发光过程的内部物理机制，并最终探索出制备高效InGaN基红光LED的最佳结构参数和生长工艺。

作为三基色之一的红光InGaN基LED在照明、显示和探测等领域有着广阔的应用前景。长期以来，由于材料生长技术等难题一直没有克服、InGaN基红光LED难以实现，使得白光LED都是通过基于高亮InGaN基蓝光激发黄色荧光粉获得的，这使得在显色指数、能量转换效率和器件微型化（集成化）方面难以达到商品化要求。因此，研究探讨InGaN基红光LED的制备工艺，理解其内部载流子的产生、传输和复合发光的物理机制，对于该领域和相关领域的材料生长和器件开发都具有重要的理论价值和现实意义。为了解决InGaN生长过程中“低温下结晶质量差、高温下In容易挥发”等难题，本项目在制备InGaN/GaN多量子阱基红光LED过程中采取了许多新的措施，主要如下：组分渐变（主要采取了改变In源流速、衬底温度两种生长方式，以及单侧组分渐变和两侧对称组分渐变等方式）、生长暂停（采取了关停Ga源，同时关停In源和Ga源，改变关停时间，改变关停次数等多种方式）、阱层盖帽层（分别尝试采用了不同厚度的GaN和AlN作为盖帽层）等。通过不断探索，终于实现了具有较高效率的红光（辐射波长长达约660nm）InGaN/GaN多量子阱基LED。.通过对上述样品荧光光谱的温度依赖性、激发功率依赖性和激发波长依赖性测量，以及对该样品结构质量的AFM、XRD、SEM、TEM、I-V、Raman表征，我们详细研究分析了有源区内富In团簇（准量子点）、结构缺陷（非辐射中心）、极化电场、相分离、组分起伏等的形成机制和应对方法，并进一步优化生长工艺和结构参数，使得发光波长、发光效率逐渐达到了本项目所设定的目标。同时，对其光学特性和生长工艺之间的内在关联机制（物理机制）做了详细、科学合理的阐明。这些收获请详见“研究成果”部分。