Research On Cavity Facet Passivation And Device Characteristics Of High Power Semiconductor Laser Diodes

With a continuous development of technology,the material,post-process and packaging for high power semiconductor lasers has reached up to a high level,which make that those laser devices are gradually applied in laser pumping,material processing,medical treatment,and national defense field etc.With the continuous application development,especially on high power fiber pumping,laser cutting,3D shaping application,study has also been focused on the technology of high power,high brightness laser devices.For high power output of a laser device,the stability of cavity facet has become a key technology.While a laser device operation at high level currents,the internal temperature rise caused by non-irradiation recombination and cavity optical absorption especially,will deteriorate the device output properties.When the temperature rises high enough,the catastrophic optical damage?COD?phenomenon on cavity facets will occur,and the device finally get in failure in an irreversible process.Therefore,special measures are used to improve the stability of the laser devices.Researchers have found that COD was caused mostly by the surface states on cavity facets,and surface passivation could improve the stability of the facet by effectively reducing the surface states concentration.Experiments on facet treatments were carried out based on analysis on the occurring mechanism of COD.These experiments included wet sulfuration,wet nitridition,sulfur-plasma passivation,nitrogen-plasma passivation,sulfur-nitrogen-plasma passivation,etc.Some of these passivation processes were used in the process of 980 nm InGaAs strained QW semiconductor lasers,an obvious passivation effect have been obtained.Main contents for the research are as the following:1.First,quantum well semiconductor laser output characteristics has been introduced,then the mechanism of COD generation has been analyzed,which would seriously affect the output characteristics of a laser device.The surface state on cavity facets is believed to be the main cause of COD.A detailed introduction to the application of plasma technology,and the application of plasma technology in the surface passivation of semiconductor lasers were given in this paper.The theory about the design and optimization of the cavity facet coating is also provided to achieve a high output power and high stability operation for semiconductor lasers.2.Research on wet sulfur passivation and wet nitrogen passivation was carried out separately.Wet sulfur passivation experiments showed that the wet sulfur passivation effect was not stable,and a poor surface morphology with serious etching and pollution is also the major disadvantage.Hydrazine was used as wet nitrogen passivation solution for obtaining a stability passivation on GaAs.With optimization of the process,a good stability passivation effect by wet hydrazine solution has been achieved,and the processed GaAs sample shows a smoother and clean surface,compared with wet sulfur passivation.3.The GaAs passivation by plasma was studied.Three group of GaAs samples weretreated separately by N plasma,S-Ar plasma and S-N plasma,and different passivation effects were achieved.The mechanism of PL deterioration has been analyzed.With process optimization and post-treatment by RTP annealing,the damaged GaAs surface by high-energy ion has restored,and the Ga As surface with stable performance and excellent PL properties was obtained.We compared the plasma treated samples with the wet passivation samples,and the results showed that the plasma treated samples were cleaner and more smooth,which would be more suitable for the cavity facet treatment on laser chip process.4.Research on the chip process and cavity facet treatment of 980 nm InGaAs strain QW semiconductor lasers has been done,RF sputtered AlN was used for AR coating and 3 pairs of RF sputtered Si/SiO₂ is used for HR coating.The refractive index of sputtered AlN film is about 2.1,which mean that a single AlN film will satisfy the requirement for AR coating of GaAs-based high power laser devices,the reflectivity achieved by 3 pairs of RF sputtered Si/SiO₂ is 96.7%.With facet passivation by the methods above,the COD level has an obvious increase,the best result has been achieved by S-N plasma treatment with about 100%increase on COD level.