Optical semiconductor device having ridge structure formed on active layer containing p-type region and its manufacture method

An optical semiconductor device comprising:

• a p-type cladding layer of p-type semiconductor formed over a substrate;
• an active layer including a p-type semiconductor region, not including an n-type semiconductor region and disposed over the p-type cladding layer;
• a buffer layer of non-doped semiconductor disposed on and being in contact with the active layer;
• a ridge-shaped n-type cladding layer of n-type semiconductor disposed on and being in contact with a partial surface of the buffer layer,
• wherein the buffer layer on both sides of the ridge-shaped n-type cladding layer is thinner than the buffer layer just under the ridge-shaped n-type cladding layer,
• wherein the buffer layer includes a region, a thickness of which decreases with increasing distance from the ridge-shaped n-type cladding layer, and
• wherein the active layer has a lamination structure having barrier layers each including a p-type semiconductor layer and quantum dot layers each including quantum dots distributing in-plane, the barrier layers and the quantum dot layers being alternately stacked.