808nm大功率激光二极管随机失效分析

Random Failure Analysis of the 808nm High Power Laser Diode

对10只808nm大功率激光二极管进行室温恒电流老化,4只器件出现随机失效。采用高倍显微镜、激光扫描共焦显微镜和扫描电子显微镜(SEM)等方法对失效器件的近场光斑、腔面形貌、p面形貌及谐振腔截面形貌等进行了观察分析。在失效样品的芯片腔面或内部发现了不同程度的晶体熔毁缺陷,并且发现激光二极管功率衰减幅度与熔毁缺陷的位置及严重程度有关,确认芯片有源区的晶体熔毁缺陷是导致808nm大功率激光二极管随机失效的主要模式。分析认为材料生长过程的晶体缺陷、芯片制作过程中引入的损伤粘污缺陷以及封装过程中引入的损伤缺陷可能是晶体熔毁缺陷产生的最初原因。某些缺陷在加电老化过程中不断生长变大,造成谐振腔内损耗增加,激光二极管输出功率降低;同时谐振腔内光损耗导致芯片局部温度升高,加速缺陷生长变大。这种反馈过程使缺陷生长加速,在相对较短的时间内形成大面积晶体熔毁,导致激光二极管灾变失效。提高大功率激光二极管可靠性的根本方法是降低芯片制造过程引入的缺陷,同时严格控制封装散热以及封装应力。

The 808 nm high power laser diodes were burned-in with a constant pumping current at room temperature, the random failure occurred for 4 out of 10 diodes during the process. The near field spot, cavity facet morphology, p-side morphology and cavity cross section morphology were detected and analyzed using the high power microscope, laser scanning confocal microscope and scanning electron microscope （SEM）. The different degree melt-down defects were found either on the facet or in the cavity, and it was found that the power attenuation amplitudes of the laser diodes were related to the position and degree of the meltdown defects, indicating the crystal meltdown defects in the active region of the chip to be the primary random failure mode of the 808 nm high power laser diodes. The analysis indicates that the crystal defects in the material growth process, damages and contaminations induced in the manufacturing process and damages induced in the packaging procedure are the origins of the meltdown defects for the crystal. Besides, some defects above grow large during the burned-in process, and cause the increase of the cavity loss and the decrease of the diode output power. Meanwhile the optical loss in the resonant cavity leads to the increment of the local region temperature of the chip and the enlargement of the defects, and the feedback process makes the defects grow large. The large area crystal meltdown occurring in a relative short period of time leads to the catastrophic failure of the laser diode. Reducing the defects introduced in the manufacturing process and strictly controlling the heat dissipation and stress of the packaging were considered as the basic methods to improve the reliability of the high power laser diodes.