Planar native-oxide AlxGa1−xAs-GaAs quantum well heterostructure ring laser diodes

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Abstract
Native‐oxide planar AlxGa1−xAs‐GaAs quantum well heterostructure ring laser diodes (25‐μm‐ wide annulus, 250‐μm inside diameter, 300‐μm outside diameter) are demonstrated. The curved cavities (full‐ring, half‐ring, and quarter‐ring) are defined by native oxidation (H2O vapor+N2 carrier gas, 450 °C) of the entire upper confining layer inside and outside of the annulus. The native oxide provides current confinement and a sufficiently large lateral index step, and thus photon confinement, to support laser oscillation along the ring. Half‐ring laser diodes fabricated in a self‐aligned geometry exhibit continuous wave (cw) 300‐K thresholds as low as ∼105 mA (∼500‐μm circular cavity length), high total external differential quantum efficiencies (∼49%), and cw output powers of ≳40 mW.