Method of manufacturing laser diode

A method of manufacturing a laser diode comprising the steps of:

• growing an active layer, a first InP layer, and a diffraction grating layer in that order on a semiconductor substrate having a first region and a second region;
• forming an alignment mark having a recess by etching the diffraction grating layer and the first InP layer in the first region of the semiconductor substrate;
• forming a first etching mask having a pattern for forming a diffraction grating, the first etching mask covering the alignment mark;
• forming a diffraction grating in the diffraction grating layer using the first etching mask;
• forming a modified layer containing InAsP, after removing the first etching mask, on an inner wall surface of the recess of the alignment mark by supplying a first source gas containing As and a second source gas containing P;
• growing a second InP layer, after forming the modified layer, on the diffraction grating layer and on the alignment mark;
• forming a second etching mask on the second InP layer, the second etching mask having an opening located in the region where the alignment mark is formed;
• selectively etching the second InP layer embedded in the recess of the alignment mark through the second etching mask by using the modified layer serving as an etching stopper;
• and
• forming a waveguide structure in a predetermined region of the diffraction grating using the alignment mark.