Optical semiconductor device

An optical semiconductor device comprising:

• a stripe-form optical waveguide layer formed on a main surface of a semiconductor substrate and having a strained quantum well constituted by first semiconductor layers which each have a thickness of less than the de Broglie wavelength of electrons and which do not lattice-match with said substrate, and second semiconductor layers which each have a forbidden bandwidth larger than that of said first semiconductor layers and which are respectively disposed on both sides of a corresponding one of said first semiconductor layers;
• and
• a blocking layer formed of semiconductor having a forbidden bandwidth larger than that of said second semiconductor layer and formed at the sides of said optical waveguide layer;
• wherein the average lattice constant of a side region of said blocking layer which is adjacent to a non-parallel interface which lies between said blocking layer and said first and second semiconductor layers and which is not parallel to the main surface of said substrate has a value between the lattice constants of said substrate and said first semiconductor layer.

An optical semiconductor device comprising:

• a stripe-form optical waveguide layer formed on a main surface of a semiconductor substrate and having a strained quantum well constituted by first semiconductor layers which each have a thickness of less than the de Broglie wavelength of electrons and which do not lattice-match with said substrate, and second semiconductor layers which each have a forbidden bandwidth larger than that of said first semiconductor layers and which are respectively disposed on both sides of a corresponding one of said first semiconductor layers;
• and
• a blocking layer formed of semiconductor having a forbidden bandwidth larger than that of said second semiconductor layer and formed at the sides of said optical waveguide layer;
• wherein a composition changing region whose average lattice constant is changed continuously or stepwise between that of said optical waveguide layer and that of said blocking layer is formed in a boundary portion between said optical waveguide layer and said blocking layer.