We investigated the influence of growth pressure and V/III ratio on selectively grown InGaAs/InGaAsP MQW by using low-pressure metalorganic vapor phase epitaxy (MOVPE). Diffusion parameters were determined from curve fitting to experimental data by using the diffusion equation. The diffusion length decreased with the increase of growth pressure. The growth enhancement at the center of the mask opening increased and saturated over growth pressure of 100 mbar. The uniformity of PL intensity along the lateral direction was improved with the decrease of growth pressure and V/III ratio. We also realized a 1.55 mum SSC-LD with vertically tapered thickness waveguide. The device exhibited a far field angle of 6.9 degrees x 12.4 degrees and a slope efficiency as high as 0.31 W/A.