Optical semiconductor device and method for producing same

An optical semiconductor device production method comprising the steps of:

• forming a projecting portion on a first-conductivity-type semiconductor substrate through etching;
• epitaxially growing intermediate layers on both sides of the projecting portion;
• sequentially epitaxially growing a first-conductivity-type first cladding layer, an active layer, and a second-conductivity-type second cladding layer at surfaces of the projecting portion and the intermediate layers;
• forming, through etching, a stripe-shaped mesa structure whose center coincides with a center of the projecting portion and which is formed of the first cladding layer, the active layer, and the second cladding layer;
• epitaxially growing buried layers for blocking current, on both sides of the mesa structure;
• and
• epitaxially growing a second-conductivity-type contact layer at surfaces of the mesa structure and the buried layers, wherein
• a width between ends of the intermediate layers that contact with the projecting portion in a stripe width direction is formed to be greater than a width between ends of bottom portions of the mesa structure in the stripe width direction,
• the mesa structure is formed to have, on each of both sides thereof, a side surface along a direction perpendicular to a surface of the semiconductor substrate, a bottom portion on the intermediate layer side, and a slope surface connecting the side surface and the bottom portion,
• the buried layers are each formed by three layers that are a second-conductivity-type or high-resistance first buried layer, a first-conductivity-type second buried layer, and a second-conductivity-type third buried layer, which are sequentially laminated on both sides of the mesa structure, and
• a distance from a part at which a plane along the side surface of the mesa structure and a plane where the intermediate layer contacts with the first buried layer cross each other, to an end on a side where the intermediate layer contacts with the first buried layer, is not less than a distance obtained by multiplying a distance from the plane where the intermediate layer contacts with the first buried layer to an upper end of the active layer by 0.708.