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

•We develop AlGaInP–GaInP MQWs ridge-waveguide LDs with DBR passivation.•The LDs obtain stable lateral mode profiles and better electrical characteristics.•The DBR passivation avoids the metal absorption and improves the scattering loss.•The LDs coated with Al2O3/Ta2O5 DBR have better temperature characteristics.

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/Ta2O5 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°.