基于隧穿结结构的GaN基极化反转黄、红光LED制备与关键科学问题研究

The high efficient GaN based yellow and red LEDs have important application values in the field of semiconductor lighting and display. At present, the highly efficient GaN yellow and red LEDs have the following main problems: 1) How to prepare the high quality InGaN quantum well with high In components. 2) How to increase recombination luminous efficiency of electrons and holes influenced by the strong polarization field in quantum well. This project proposes to develop the Ga polar surface polarization reversed GaN based yellow and red LEDs with tunneling junction, and the key scientific issues for this research was also investigated. For this device structure, the electronic injection InGaN layer can be grown on the quantum well at low temperature, avoiding of quantum well layer damage of the p-GaN high temperature growth process of conventional LED structure. The reversed polarization quantum well was used to improve the recombination efficiency of electrons and holes. At the same time, the n-InGaN current spreading layer can be introduced due to exist of tunneling junction to overcome poor current spreading problem of the p - GaN layer for this device structure. This project will focus on the realization of tunneling junction with high tunneling current density and low contact resistance, clarifying growth recombination mechanisms of high In composition InGaN quantum well. This project is to obtain GaN based yellow and red LED for more efficient semiconductor lighting, laying the theoretical and experimental basis of GaN based yellow and red laser, and the development of full spectrum solar cell.

高效GaN基黄、红光LED在半导体照明与显示等领域具有重要应用价值。目前，高效GaN基黄、红光LED还存在以下主要问题：1）高质量高In组份InGaN量子阱难以制备；2）高In组份量子阱内强极化场引起电子与空穴复合发光效率降低。本项目提出研制基于隧穿结结构的Ga极性面极化反转GaN基黄、红光LED并进行关键科学问题研究。该结构中InGaN电子注入层可低温生长于量子阱层之上，避免常规LED顶层p-GaN高温生长过程对量子阱层造成的损伤；利用量子阱内极性反转特性，提高量子阱内电子与空穴复合发光效率。由于隧穿结的存在，可以引入n-GaN电流扩展层，从而克服p-GaN层电流扩展差的问题。该项目重点在于特性良好的隧穿结，阐明高In组份InGaN量子阱的生长及复合发光机理。本项目将获得性能良好的GaN基黄、红光LED，为更高效半导体照明、GaN基黄、红光光激光器及全谱太阳能电池研究奠定理论与实验基础。

本项目执行期间主要工作有：基于高In组分InGaN薄膜表面形貌的演化规律，提出InGaN表面岛比例的自规则演化模型，阐明了高In组分InGaN的表面形貌演化机制。通过将InGaN插入层退火，有效降低GaN背景载流子浓度，获得方块电阻高达2.1×108 Ω/square非故意掺杂高阻GaN薄膜。建立了孔洞和In沉淀形成的物理模型，成功解释了InGaN/GaN双异质结的发光淬灭机制。建立了In沉淀的自成键模型，将In沉淀的本质归结于独立的In沉淀+孔洞的复合体，成功解释了常见的高In组分InGaN MQWs或InN薄膜中含有较多In沉淀且发光量子效率很低的原因。系统研究了生长温度和Mg流量对In辅助p-GaN晶体质量和电学性质的影响，制备出Ga极性pdown极化反转结构黄光LED，MQWs的室温PL峰FWHM较大说明高In组分的MQWs中In组分不均匀现象更加显著。制备的LED器件随着电压升高，EL峰的蓝移仅15 nm，证实极化反转结构确实能够克服MQWs内的极化电场引起的QCSE的负面作用，表明这种Ga极性p-down极化反转结构LED在发展长波长LED方面具备很大潜力。