基于InGaN量子点的发光二极管载流子复合动力学研究

Investigation of Carrier Recombination Dynamics of Light-Emitting Diode Based on InGaN Quantum Dots

InGaN半导体材料具有带隙宽度通过改变In组分可调的特点,被广泛应用在新一代光电子器件中,但绿光LED依然存在"绿隙(green gap)"问题有待解决。本文深入研究载流子复合机制,为解决"绿隙"提供新思路。利用光致荧光光谱(PL)和时间分辨光谱(TRPL)研究了不同温度下对应不同光子能量的InGaN量子点(QDs)发光二极管器件的载流子复合动力学过程,得到了InGaN QDs的瞬态光致发光特性和辐射/非辐射复合的瞬态寿命。稳态光致发光谱在15~300 K的温度范围内,峰值出现先蓝移再红移(S-shaped)的偏移现象,发射峰值蓝移约4.2 meV,在60 K时达到最大值,随后发射峰红移,形成随温度呈S形的变化。这种变化说明QDs结构中载流子局域化行为,激子复合是InGaN量子点绿光发射的主要原因。通过拟合不同温度下的归一化PL积分强度,获得激活能Eact约为204.07 meV,激活能较高,证明了InGaN量子点具有较强的载流子限制作用,可以更好抑制载流子向非辐射复合中心迁移,内量子效率(internal quantum efficiency)为35.1%。InGaN QDs中自由载流子复合的平均复合寿命τrad=73.85ns。能量边界值Eme=2.34 eV远高于局域深度E0=62.55 meV,可见能级完全低于迁移率边缘,因此InGaN QDs寿命衰减归因于载流子局域态复合。通过使用改进的光谱数据分析手段对基于内嵌量子点新结构的荧光器件进行研究,得到了有意义的结论,为进一步了解InGaN量子点内部发光机理和研制新一代照明器件提供借鉴,说明引入InGaN量子点对光电器件的发展具有很好的推动作用。

InGaN semiconductor materials are widely used In a new generation of optoelectronic devices because of their adjustable bandgap width by changing In components. However,the green LED still has a "green gap" problem to be solved. In this paper, the carrier recombination mechanism is studied in depth to provide a new idea for solving a "green gap". The photoluminescence spectrum(PL) and time-resolved photoluminescence spectrum(TRPL) were used for investigating the carrier recombination processes of InGaN quantum dots(QDs) LED devices with different photon energies at temperatures. The transient photoluminescence properties of InGaN QDs and the transient life of radiative/nonradiative recombination were obtained. In the temperature range from 15 to 300 K, the peak value of the steady-state photoluminescence spectrum has its first blue shift and then red shift(s-shaped). The blue shift of the emission peak is about 4.2 meV, reaching its maximum value at 60 K, followed by the red shift of the emission peak, forming an s-shaped change with temperature. This change indicates that carrier localization behavior in QDs structure, and exciton recombination is the main reason for green light emission of InGaN QDs. By fitting the normalized PL integral intensity at different temperatures, the activation energy Eact was about 204.07 meV, with high activation energy, which proved that the InGaN QDs have strong carrier limiting effect and can better suppress the transitions to the nonradiative recombination centers. The internal quantum efficiency was estimated at 35.1%. Free carrier in the InGaN QDs composite average composite life τrad=73.85 ns. The energy boundary value Eme=2.34 eV is much higher than the local depth E0=62.55 meV, and it can be seen that the energy level is completely lower than the mobility edge, so the decay of InGaN QDs life is attributed to carrier local state recombination. In this study, the improved spectral data analysis method was used to study the fluorescence device based on the new structure of embedded QDs, and meaningful conclusions were obtained. It provides a reference for further understanding of the internal luminescence mechanism of InGaN quantum dots and the development of a new generation of lighting devices, indicating that the introduction of InGaN quantum dots plays a good role in promoting the development of photoelectric devices.