Patent ID: 7038233

Claim:
A semiconductor optical device, comprising: an InP substrate; an active region formed above the InP substrate, said active region being comprised of a quantum well structure; optical guiding layers each formed on and under said active region; and clad layers; wherein on sides in the direction crossing the light-emitting direction, the sides of the active region are buried with semiconductor layers having band gap energy greater than that of a quantum well layer; and wherein a composition of Al of the quantum well layer is in the group consisting of InGaAlAs compound semiconductor layers, a composition ratio of the Al being in the range of 0 to 0.13, both inclusive, wherein the InGaAlAs is in the group consisting of compositions A (In: 0.87, Ga: 0, Al: 0.13), B (In: 1.0, Ga: 0, Al: 0), C (In: 0, Ga: 1.0, Al: 0), and D (In: 0, Ga: 0.87, Al: 0.13) in the composition diagram of the four-element based compound semiconductor materials (In 1−x−y Ga x Al y As).