Deep-Etched Native-Oxide-Confined High-Index-Contrast AlGaAs Heterostructure Lasers With 1.3 $\mu$m Dilute-Nitride Quantum Wells

Using a modified, O$_{2}$-enhanced nonselective wet thermal oxidation process, deep-etched ridge waveguides in AlGaAs heterostructures containing $\lambda = 808$ nm InAlGaAs single quantum well or aluminum-free $\lambda = 1.3$ $\mu$ m GaAsP/InGaAsN dilute nitride multi-quantum-well active regions have been directly oxidized to effectively provide simultaneous electrical isolation, interface state passivation, and sidewall roughness reduction. The resulting high-index-contrast (HIC) ridge waveguide (RWG) diode lasers show improved performance relative to conventional shallow-etched devices owing to both strong optical confinement and the complete elimination of current spreading, with 5 $\mu$m stripe width dilute-nitride devices showing up to a 2.3 times threshold reduction and strong index guiding for kink-free operation. Oxidation of an AlGaAs graded-index separate confinement heterostructure is studied for varying O$_{2}$ concentrations, and the interface passivation effectiveness of the native oxide is studied through comparison with deposited SiO$_{2}$ and via a study of the stripe-width dependence of internal quantum efficiency and modal loss. The HIC RWG structure is shown to enable the operation of half-racetrack-ring-resonator lasers with a bend radius as small as $r = 6$ $\mu$m.