Optical semiconductor element, semiconductor laser, and method of manufacturing optical semiconductor element

A semiconductor laser comprising:

• an active layer disposed over a substrate;
• a grating base layer including a projection-recess structure disposed in the vicinity of the active layer;
• a grating cover layer disposed including a group III-V semiconductor having three or more elements;
• and
• a pair of electrodes for an injection of a current to the active layer,
• wherein the grating cover layer includes a first region which is disposed over recessed portions of the grating base layer and which includes a compositional ratio of a group III-V semiconductor having a first refractive index, and a second region which is disposed over projecting portions of the grating base layer and which includes a compositional ratio of a group III-V semiconductor having a second refractive index that is smaller than the first refractive index;
• and
• wherein the grating base layer includes a group III-V semiconductor having a refractive index that is smaller than the first refractive index.

A method of manufacturing an optical semiconductor element comprising:

• forming a grating base layer including a group III-V semiconductor over a substrate;
• forming a periodic projection-recess structure in the grating base layer;
• forming a group III-V semiconductor over recessed portions of the grating base layer, the group III-V semiconductor including three or more elements having a first compositional ratio and a first refractive index;
• and
• forming a group III-V semiconductor over projecting portions of the grating base layer, the group III-V semiconductor including three or more elements having a second compositional ratio and a second refractive index that is smaller than the first refractive index,
• wherein the grating base layer includes the group III-V semiconductor having a refractive index that is smaller than the first refractive index.