High-performance planar native-oxide buried-mesa index-guided AlGaAs-GaAs quantum well heterostructure lasers

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Abstract
High-performance planar ‘‘buried-mesa’’ index-guided AlGaAs-GaAs quantum well heterostructure (QWH) lasers have been fabricated by oxidation (H2O vapor+N2 carrier gas, 425–525 °C) of a significant thickness of the high composition AlxGa1−xAs upper confining layer (outside the active stripe). The oxide provides excellent current confinement for low-threshold laser operation and a low refractive index (n∼1.6) for transverse optical confinement and index guiding. Laser diodes with ∼4 μm-wide active regions exhibit 300 K continuous (cw) laser thresholds of 8 mA, with single longitudinal mode operation to 23 mW/facet, and maximum output powers of 45 mW/facet (uncoated). Devices fabricated on a lower confinement AlxGa1−xAs-GaAs QWH crystal (x≲0.6 instead of x≳0.8) with ∼4 μm-wide active stripes exhibit 300 K cw thresholds of 9 mA and total external differential quantum efficiencies of 66%. Peak output powers ≳80 mW/facet (uncoated) with linear L-I characteristics over the entire operating range are observed. In limited ‘‘lifetest’’ these laser diodes have been operated ≳500 h without significant degradation.