Nonselective oxidation of GaAs-based III-V compound semiconductor heterostructures for in-plane semiconductor lasers

Abstract

A nonselective wet thermal oxidation technique for AlGaAs-containing heterostructures has been shown to enable the fabrication of a variety of novel high-efficiency, high-power GaAs-based in-plane laser devices. Applied in conjunction with a deep anisotropic dry etch, nonselective oxidation yields a simple, self-aligned high-index-contrast (HIC) ridge waveguide (RWG) structure. The native oxide grown directly on the waveguide ridge simultaneously provides excellent electrical insulation, passivation of the etch-exposed bipolar active region, and a low refractive index cladding, leading to numerous laser performance benefits. The resulting strong lateral optical confinement at the semiconductor/oxide interface (with refractive index contrast n~1.7) enables half-racetrack ring resonator lasers with a record small 6 µm bend radius. A nearly circularly-symmetric output beam is demonstrated on narrow w=1.4 µm aperture width straight stripe-geometry lasers with single spatial and longitudinal mode total power output of ~180 mW at 228 mA (9x threshold). With the complete structural elimination of lateral current spreading, the excellent overlap of the optical field with the gain region provides high slope efficiency performance (ranging from >1.0 W/A at w=1.4 m to 1.3 W/A for w=150 m broad area stripes) for 300 K cw operation of unbonded, p-side up 808 nm InAlGaAs graded-index separate confinement heterostructure (GRINSCH) active region lasers. Using the direct thermal oxidation of a dilute nitride GaAsP/InGaAsN MQW active region, 1.3 µm emission GaAs-based HIC RWG lasers exhibit a >2X threshold reduction and kink-free operation relative to conventional low-confinement devices. Other recent progress on the application of nonselective oxidation to GaAs-based semiconductor lasers will be reported.