Method distributed feedback semiconductor laser for fabricating

A method for fabricating a distributed feedback semiconductor laser, comprising the steps of:

• forming a gain-coupled diffraction grating on a semiconductor substrate;
• and
• forming a semiconductor multi-layer structure including an active layer for generating laser light on the diffraction grating, wherein the step of forming the diffraction grating includes the steps of:
• forming a plurality of curved projections periodically arranged at a surface at a surface of the semiconductor substrate by lithography and etching;
• and
• covering the plurality of curved projections with a light absorption layer including a light absorption area having a first thickness at each border between two adjacent curved projections and a non-light absorption area having a second thickness which is smaller than the first thickness at a top of each of the curved surfaces, the light absorption area being formed to have a band gap which is narrower than a band gap of the active layer and the non-light absorption area being formed to have a band gap which is wider than the band gap of the active layer.

A method for fabricating a distributed feedback semiconductor laser, comprising the steps of:

• forming a gain-coupled diffraction grating on a semiconductor substrate;
• and
• forming a semiconductor multi-layer structure including an active layer for generating laser light on the diffraction grating, wherein the step of forming the diffraction grating includes the steps of:
• depositing a first semiconductor layer on the semiconductor substrate;
• forming a plurality of projections and grooves periodically arranged at a surface of the first semiconductor layer by lithography and etching;
• covering the plurality of projections and grooves with a light absorption layer including a light absorption area having a first thickness at each of the grooves between two adjacent projections and a non-light absorption area having a second thickness which is smaller than the first thickness at a peak of each of the projections, the light absorption area being formed to have a band gap which is narrower than a band gap of the active layer and the non-light absorption area being formed to have a band gap which is wider than the band gap of the active layer;
• and
• depositing a second semiconductor layer on the light absorption layer so as to have a band gap which is wider than a band gap of the first semiconductor layer.

A method for fabricating a distributed feedback semiconductor laser, comprising the steps of:

• forming a gain-coupled diffraction grating on a semiconductor substrate;
• and
• forming a semiconductor multi-layer structure including an active layer for generating laser light on the diffraction grating, wherein the step of forming the diffraction grating includes the steps of:
• forming a plurality of projections and grooves periodically arranged by lithography and etching on a surface of the semiconductor multilayer structure formed on a surface of the semiconductor substrate;
• and
• heating the projections and grooves with a gas phase atmosphere of a heat treatment apparatus, the gas atmosphere including AsH.sub.3 to form a light absorption layer of InAsP so that a plurality of parts of the light absorption layer are respectively located in the grooves.