The Catastrophic Optical Damage Monitoring And Failure Mechanism Study Of High Power GaAs-based Semiconductor Laser Diodes

High power semiconductor laser diodes have many advantages such as high optical output power,wide wavelength range,simple power supply mode,high power conversion efficiency,small chip size and high stability,which make it widely used in laser printing,medical correction,laser ranging and other fields,and this requires higher device performance and reliability.In this paper,the 808-nm high-power GaAs-based semiconductor laser diodes are the study object.The transient COD processes of their output facets are monitored in real-time mode by the optical fiber measurement system we design and set up,and we use a variety of failure analysis techniques to investigate the failure mechanisms of the transient failure and long-term-aging failure laser diode samples.This paper has done the following parts of studies in experiment and theory.1.This paper proposes a convenient,optical-fiber-measurement-based failure monitoring technique of output facet COD,which realizes the real-time monitoring and recording of the transient COD process of 3.5-W 808-nm GaAs-based laser diodes.This technical method uses an optical system based on the 1550-nm fiber coupled laser diode illuminant and photodiode detection to measure the facet reflectivity of the tested device in real-time mode.Its temporal resolution of 2 ns is able to monitor the COD process,which happens within tens of nanoseconds,in a transient,real-time mode.The experiment results show that under the pulsed driving current,the facet reflectivity of the 808-nm tested device towards the 1550-nm test laser dropped rapidly from 28%to2%within 20³0 ns,and the reflectivity decline rate is about 1.4%/ns.This process accurately characterises the outburst of the transient COD of output facet,and the COD seeds formed within 20³0 ns,which is 10 ns shorter than that of the 980-nm devices.2.The transient-COD-experienced device and an undamaged device are studied by FIB,HRTEM and EDS.At first,the HRTEM samples of the tested devices are prepared by FIB.Then,the morphology and microstructure of samples are observed by HRTEM,and the element composition and content of samples are analyzed by EDS.By comparing the experiment results of two samples,the transient failure mechanism are summed up:Under high-amplitude driving currents,the Si coating film at output facet of the tested device was burnt out and volatilized,so it loses its protective effect for the Al₂O₃ output facet.This results in the facet being burnt out by the accumulated heat and its turning into an uneven surface within tens of nanoseconds.In addition,the AlGaInAs quantum well is also burnt out during COD process,and its lattice structure is badly damaged.The Si coating film outside the active region become diffused and oxidized,resulting in the degradation of its performance.3.The failure mechanism of the long-term-aging-COD-experienced device are studied by infrared thermal camera,emission microscope,FIB,HRTEM and EDS technology.By analyzing the experiment results comprehensively,the following long-term-aging failure mechanism are summed up:During the constant temperature and constant current aging process,the Si coating film at output facet of the tested device become diffused and oxidized gradually,leading to the changes of its thickness and refractive index,and this results in the fluctuation of its reflectivity and the degradation of its protective performance.Finally,the output facet is burnt out by the accumulated heat,and COD seeds appear on facet.By now,the device is failed.In addition,COD seeds have higher facet temperature,and there are reverse light leak within them.Unlike the transient failure,the long-term-aging failure of laser diodes is a slow process.Under normal operating condition,the gradual degradation of device finally leads to the catastrophic optical damage of the output facet and the device failure.