Radio Frequency Plasma-Enhanced Reactive Magnetron Sputtering Deposition of α-SiN x on Photonic Crystal─Laser Diodes for Facet Passivation

Amorphous silicon nitride (α-SiNx) films were coated on a photonic crystal-laser diode by the radio frequency magnetron sputtering method. Sputtering deposition conditions were changed to obtain α-SiNx films with different properties. The optical parameters and morphologies of the products were systemically characterized by spectroscopic ellipsometry fitting, energy-dispersive X-ray spectroscopy, atomic force microscopy, and performance of LDs coated with α-SiNx films were tested at 25 °C. Physical mechanisms of sputtering were explained in detail. α-SiNx with a band gap of 4.4 eV and a refractive index of 2.03 at 980 nm were grown. The extinction coefficient equal to 0 at 980 nm, and the surface morphology tended to be homogeneous and dense. The main influencing factors related to the catastrophic optical mirror damage (COMD) phenomenon were investigated. Then plasma pretreatment was implemented to eliminate defects and improve the cavity surface quality and further optimized by measuring the intensity of photoluminescence. Afterward, a rapid annealing method was also carried out to improve coating performance. Finally, α-SiNx acted as a passivation layer in the antireflection film coated on the LD facet, and the COMD threshold increased from 5 to 15.2 W, which led to a higher reliability than nonoptimized LDs and elimination of the COMD phenomenon.