Effect of passivation layers on characteristics of AlGaInP ridge waveguide laser diodes

We investigate the effect of passivation structure on the optical mode distribution and characteristics of the edge emitting ridge waveguide AlGaInP-GaInP visible laser diodes (LDs). For conventional designs of single-layer Si₃N₄ or SiO₂ passivation, the variation of lateral near-field confinement and the horizontal far-field (FF) divergence can be determined via the modification of dielectric layer thickness. Thin passivation layer suffers from high absorption at the metal interface while thick passivation layer suffers from poor heat dissipation in the ridge waveguide and high scattering loss, resulting in high threshold. We propose a novel design of three-pair Al₂O₃/Ta₂O ₅ multilayer optical thin films as passivation on the ridge waveguide, which can improve the laser characteristics and the heat dissipation. The measured room-temperature threshold current (Ith) and characteristic temperature (T₀) are 44.5 mA and 104.2 K with a divergence angle of 16.4.