The effects of As2 pressure on the InAs heteroepitaxial growth on a vicinal GaSb substrate by solid-source molecular beam epitaxy were investigated. Transition layers with small lattice constants compared with GaSb caused by As/Sb exchange were observed at various pressures. When the As2 pressure was high, misfit dislocations were observed at the interface transition layer. As the As2 pressure decreased, misfit dislocations disappeared with the reduction in transition layer thickness, whereas pits were formed. From the result of strain analysis, dislocations were found to accompany lattice relaxation, whereas pits were formed by excess As2 pressure. By further reducing the As2 pressure, a high-quality pseudomorphic InAs layer free from dislocations and pits was obtained.
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Diffraction limited λ = 2–2.2 µm 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 6 µm 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.
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