Optical semiconductor device and method for producing same

1 . An optical semiconductor device comprising:

a first-conductivity-type semiconductor substrate having a projecting portion;

second-conductivity-type intermediate layers formed on both sides of the projecting portion above the semiconductor substrate;

a stripe-shaped mesa structure formed of a first-conductivity-type first cladding layer, an active layer, and a second-conductivity-type second cladding layer, which are laminated above a surface including a top of the projecting portion so as to be centered at the projecting portion;

buried layers formed on both sides of the mesa structure, to block current; and

a second-conductivity-type contact layer formed 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 greater than a width between ends of bottom portions of the mesa structure in the stripe width direction,

the mesa structure has, 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 of 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.

2 . The optical semiconductor device according to claim 1 , further comprising:

a surface protection film formed above the second-conductivity-type contact layer and having an opening;

a first electrode contacting with a surface of the second-conductivity-type contact layer via the opening of the surface protection film; and

a second electrode formed on a back surface side of the first-conductivity-type semiconductor substrate.

3 . The optical semiconductor device according to claim 1 , wherein

the first buried layer is formed of a side surface portion covering the side surface of the mesa structure, a slope portion covering the slope surface of the mesa structure, and a flat portion covering a surface of the intermediate layer.

4 . The optical semiconductor device according to claim 2 , wherein

a layer thickness of the flat portion in the first buried layer is not less than two times a layer thickness of the side surface portion.

5 . 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.

6 . The optical semiconductor device production method according to claim 5 , wherein

etching is performed so that a sectional shape along a stripe width direction of the projecting portion becomes a rectangular shape or a trapezoidal shape.