InGaN/GaN多量子阱中声子与激子耦合行为研究

InGaN/GaN multiple quantum wells, are the active region of high brightness blue and green light emitting diodes. Strain and localized states are featured by the multiple quantum wells and have decisive influence on the device performance. The strain of quantum wells under luminescence is difficult to be determined by current research. The phonon-exciton coupling contains information on the strain and exciton localization of the quantum wells under luminescence. This project intends to focus on the phonon replicas in the low-temperature electroluminescence spectra. Based on the longitudinal optical (LO) phonon frequency and the coupling strength derived from the phonon replicas, the strain of the quantum wells under luminescence and exciton localization are expected to be determined. The contents include: (1) research on the strain variation of the quantum wells with injection current and the corresponding mechanism; (2) research on the influence of growth method and structure of the multiple quantum wells on the exciton localization and the mechanism. Two achievements are expected from this project. The first is the development of the LO phonon frequency detection into a brand new method in characterizing the strain of quantum wells under luminescence; The second is the realization of a breakthrough in understanding the luminescence mechanism of InGaN quantum wells through systematic research on the influence factor of the exciton localization and its effect on the device performance. Based on these achievements, the optimization of the structure and growth parameters of the quantum wells could be realized.

InGaN/GaN多量子阱是高亮度蓝光和绿光LED的有源区，应变和局域态是量子阱的两大特性，对器件性能有决定性的影响。目前研究难以表征量子阱发光时的应变，声子与激子的耦合包含量子阱发光时应变与激子局域化信息。本项目拟着眼于量子阱低温电致发光谱的声子伴线，根据纵光学声子频率和耦合强度研究量子阱发光时的应变和局域态。内容包括：（1）不同电流密度下发光阱应变变化及机理；（2）量子阱生长方法和阱垒结构影响激子局域化程度和器件性能的机理。本项目有望：第一，将GaN基LED中声子与激子耦合频率的探测发展为对量子阱发光时应变进行表征的一种全新手段；第二，通过系统研究激子局域化影响因素以及对器件性能的影响机理，在InGaN量子阱发光机理的认识上实现新的突破，并在此基础上改进量子阱结构与优化生长条件，提升器件性能。

InGaN/GaN多量子阱结构广泛应用于蓝色和绿色发光器件中。InGaN量子阱的应变和材料的局域态，对器件性能具有重要影响。本项目研究用量子阱中声子与激子耦合行为，包括一级与零级声子峰的能量间隔(“能量间隔”)以及耦合强度（黄昆因子），研究了载流子在量子阱的局域态中的变化。.1.硅衬底蓝光LED的InGaN/GaN多量子阱中: 100-150 K，能量间隔随电流密度的增加呈先升后降再升的水平“S”型变化。200-300 K，能量间隔在低电流密度下无显著变化，大电流密度下，能量间隔随电流的增大而增大。.2.硅衬底绿光LED的InGaN/GaN多量子阱中。（1）100-150 K，能量间隔随电流密度的增大而先降后升；200-250 K，能量间隔随电流密度的增加呈先升后降再升的水平“S”型变化。（2）100-150 K，黄昆因子随电流密度的增大而先升后降。200-250 K，黄昆因子随电流增加而先降后升再降。.3.硅衬底黄光LED的InGaN/GaN多量子阱中。(1) 能量间隔随电流密度的增加而先降后升，在初始减少段，随着温度的上升，能量间隔随电流增加而降低的幅度逐渐增加，能量间隔由降变升的拐点所对应的电流密度逐渐增大。（2）黄昆因子与能量间隔呈反相变化。黄昆因子随电流密度的增加而先增后减，在初始增加段，增加的幅度随温度的升高而增加，且随温度的升高，黄昆因子随电流密度的增加由降转升的电流密度增大。.随着波长从蓝光到绿光再到黄光，In组分增加，能量间隔先增后减，黄昆因子则呈现单调增大的趋势。.能量间隔和黄昆因子的上述变化，本项目将其归结为不同温度和电流密度下，载流子在量子阱的局域态中的不同分布造成。