GaN基绿光激光器外延结构的应力弛豫机制及退化机制的研究

GaN-based green laser diodes have a wide range of potential applications in laser display, portable projector, medical equipment, deep-sea probing, underwater communication etc. Although green laser diodes have been commercialized, it is known very little of the failure and degradation mechanisms under cw operation. In particular, no evidence of the correlation between microstructure and reliability can be provided. In this research proposal the stress relaxation mechanism of green laser diode with varied cladding layer thickness will be studied first. By combining multi-analytical techniques, such as micro-photoluminescence, micro-cathodoluminescence, transmission electron microscopy, atom probe tomography, electron beam induced current etc., micro-optical properties and microstructure of green laser diodes based on InGaN material will be investigated. By comparing strain field of the active region, Mg dopant distribution and defect types of green laser diodes before and after life-tests, the root cause that affects green laser lifetime and power be discovered. This may help further improve the performance of green lasers and accelerate their applications more widely.

GaN基绿光半导体激光器在激光显示、移动投影、医学设备、深海探测和水下通信等领域有着广泛的应用前景。尽管目前绿光激光器已经商业化，但是对其在连续输出时的失效和退化机制却知之甚少，尤其是缺少显微结构对激光器的可靠性影响的直接证据。本项目将从研究不同外延结构的绿光激光器的应力弛豫机制着手，应用现代多维分析技术-微区光致发光、微区阴极射线发光、透射电镜、聚焦离子束电镜、三维原子探针、电子束激发电流等，对基于InGaN材料的绿光激光器的微区光学性质和显微结构及成分进行研究，通过对比绿光激光器老化前后的主要缺陷类型、应力分布、Mg掺杂物扩散情况、少子扩散距离等，来研究绿光激光器性能与缺陷的关系，与应力的关系，与p型掺杂的关系，揭示制约绿光激光器寿命和发光效率的根本物理原因，进一步提高激光器的性能。该项目的研究将对绿光激光器的大规模应用起到重要的推动作用。

GaN基绿光激光器在激光显示、移动投影、医学设备、深海探测和水下通信等领域有着非常广泛的应用。本项目研究了商业化绿光激光器在电流、温度和湿度等应力条件下的老化行为及退化机制。首先研究了绿光激光器快速退化机制，发现快速退化与激光器工艺相关的缺陷有关，缺陷可能会造成局部过热而使激光器快速退化。本项目还通过光学、电学、微区光致发光谱和阴极荧光谱、透射电镜等方法研究了缓慢老化绿光激光器的退化机制。研究发现，缓慢退化会产生阈值电流增加和斜率效率下降的双重效应，这与很多文献报道的蓝紫光激光器退化行为不同，CL发现了缓慢老化激光器的退化不仅仅发生在量子阱区域，还包含了量子阱周边区域，例如波导层。进一步，本项目还研究了湿度条件对绿光激光器退化机制的影响。通过不同湿度条件进行老化，推出了GaN激光器的湿度因子约为BRH1.1X10-4/%2, 低于InP基激光器，说明湿度对GaN激光器的影响小于对InP激光器的影响，但是在高湿度下，绿光激光器发生了快速退化，说明湿度对激光器老化起明显加速作用。湿度同时还使激光器的欧姆接触退化。另外，本项目还通过三维原子探针对不同老化程度的激光器的Mg掺杂及量子阱界面结构进行了研究，发现即使是在完全退化激光器中，Mg在量子阱的浓度仍低于三维原子探针的探测极限。老化后激光器的量子阱界面粗糙度增加可能是激光器老化的结果。本项目的实施对于进一步提高绿光激光器的可靠性有重要意义。