Buried-type semiconductor optical device

A buried semiconductor optical device comprising:

• a semiconductor substrate;
• a mesa-stripe portion including a multi-quantum well layer on the semiconductor substrate;
• a buried layer consisting of a first portion and a second portion,
• the first portion covering one side of the mesa-stripe portion,
• the second portion covering the other side of the mesa-stripe portion, and
• the first portion and the second portion covering a surface of the semiconductor substrate;
• and
• an electrode configured to cause an electric current to flow through the mesa-stripe portion,
• the buried layer comprising, from the surface of the semiconductor substrate, a first sublayer, a second sublayer, and a third sublayer,
• the first sublayer, and the third sublayer each consisting of semi-insulating InP,
• the first sublayer and the second sublayer forming a pair structure,
• the first sublayer being a bottom layer of the buried layer;
• the second sublayer being located above the multi-quantum well layer from the surface of the semiconductor substrate, and
• the second sublayer consisting of one or more layers selected from a group of InGaAs, InAlAs, InGaAlAs, InGaAsP, and InAlAsP.