Single spatial mode 2-2.2 μm diode lasers fabricated by selective wet etching

Diffraction limited λ = 22.2m ridge waveguide lasers with continuous wave output power near 100 mW at room temperature were fabricated with a two-step wet etching technique using the interface between the top cladding and waveguide core materials as an etch stopper. The devices did not suffer from lateral current spreading. The second optical mode was suppressed by the low lateral confinement. Experiments showed that reducing the ridge width below 6m did not affect the device efficiency or the output beam quality but led to an increase of the transparency current density. We speculate that this increase was associated with the mismatch between the wide modal size and the narrow current path in ridge lasers with suppressed lateral current spreading.