InGaN基蓝绿光LED外延材料与器件的研究

A large lattice mismatch and thermal expansion coefficient mismatch exsit between GaN and the substrate in blue and green LEDs using InGaN/GaN quantum wells as active regions. This challenge leads to the presence of the larger LED piezoelectric polarization fields and a large number of defects and dislocations, limiting the luminous efficiency. This project suggests replacing GaN with InGaN as nucleation layer and unintentionally doped layer in GaN-based blue and green LED structure to reduce the piezoelectric polarization field and the dislocation density in these two and subsequent layers, and thus improve the luminous efficiency. Furthermore, we propose to use InxGa1-xN/InyGa1-yN multiple quantum well (MQW) as active region of blue and green LED structure. This project combines means of SEM, XRD, TEM, EL, PL, Hall measurement to study : 1) the mechanism of dislocation generation and development in InGaN nucleation layer and unintentionally doped InGaN layer; 2 ) the mechanism of growth and doping of n-InGaN and p-InGaN layer, and growth condition of n-InGaN and p-InGaN layer with high quality and high conductivity ; 3) design and growth of InxGa1-xN/InyGa1-yN layer as the active region of the blue and green LED; 4) The effect of In-component and micro structure on luminous efficiency and efficiency droop of droop of blue/green LED with acitve region of InxGa1-xN/InyGa1-yN MQW. This program will help to understand basic process and luminous of the blue/green LED structures in which GaN layers in traditional blue/green LED structures are replaced with InGaN, as well it will provide experimental and theorical data for the study of light efficiency enhancement of blue/green LEDs.

蓝、绿光LED有源区的InGaN/GaN量子阱中，GaN与衬底间存在着较大的晶格失配及热失配，阻碍了蓝、绿光LED发光效率提高。本项目以减小有源区中的压电极化场和位错密度从而提高发光效率为目标，提出用InGaN代替目前GaN基LED结构中普遍使用的GaN形核层和非故意掺杂层，并生长以InxGa1-xN/InyGa1-yN量子阱充当有源区的蓝、绿光LED结构，研究：1）InGaN形核层和非故意掺杂InGaN层的位错生成、发展机制；2）高晶体质量和高电导率的n-InGaN和p-InGaN层的生长和掺杂机理；3）以InxGa1-xN/InyGa1-yN为有源区的蓝、绿光LED的设计、生长；4）InxGa1-xN/InyGa1-yN为有源区蓝、绿光LED的发光性质和效率骤降效应与其In组分、微结构的关系。本项目有助于理解以InGaN代替蓝、绿光LED中GaN层后LED的生长过程和发光机制。

本项目以减小蓝、绿光LED有源区中的压电极化场和位错密度从而提高器件发光效率为目标，从材料生长与表征、器件结构生长与光电性能测试、器件性能理论计算三方面展开研究。利用金属有机化学气相沉积方法生长了不同In组分的InxGa1-xN外延薄膜、多量子阱结构和LED器件，揭示了III族氮化物外延薄膜生长过程中位错生成、发展过程；研究了形核层、生长温度、前驱体比例等参数对外延薄膜生长质量（表面形貌、位错密度等）和光学性质的影响规律，发展了降低位错密度的薄膜生长技术；研究了硅、镁掺杂对n型和p型半导体功能层薄膜光学、电学性质的影响规律，并阐明了相关规律的产生机制，确定了最佳掺杂比例；发现了在高In组分绿光多量子阱结构生长过程中生长模式的转变以及量子点的产生，通过调控低维量子结构使发光内量子效率提高了4倍以上；研究了插入层、量子阱厚度等参数对蓝光LED多量子阱质量和器件性能的影响规律，通过改变插入层厚度实现了对V形坑尺寸的调控，并改善了载流子注入效率，进而提高了LED的发光效率；理论研究了穿透位错密度和界面结构（极化场强度）对LED器件光电特性的影响规律，并阐明了影响机制。本项目的研究成果加深了对III族氮化物薄膜生长规律和LED器件发光机制的理解，丰富了晶体生长理论，所发展的外延生长技术为生长满足高性能LED器件乃至激光器件使用要求的高质量III族氮化物薄膜材料奠定了基础。