Patent ID: 8232125

Claim:
A method for manufacturing an optical semiconductor device comprising steps of: (a) forming an active layer having a p-type quantum dot structure over a lower cladding layer made of semiconductor material of a first conductivity type; (b) forming an upper cladding layer made of semiconductor material of a second conductivity type opposite to the first conductivity type over the active layer; (c) covering an upper surface of the upper cladding layer in an area extending in one direction, with a mask pattern; (d) by using the mask pattern as an etching mask, etching the upper cladding layer partway in a thickness direction thereof; (e) by using the mask pattern as a mask, implanting or diffusing impurities into the upper cladding layer to make the upper cladding layer have the first conductivity type or high resistance to form a capacitance reducing region; and (f) removing the mask pattern, wherein the capacitance reducing region formed in the step (e) reaches at least an upper surface of the active layer if the lower cladding layer is a p-type, and reaches at least an upper surface of the lower cladding layer if the lower cladding layer is an n-type.