Optical semiconductor device and process for producing the same
A resist is coated on a substrate. The resist is exposed to a pattern of a plurality of diffraction gratings for setting pitches corresponding respectively to oscillation wavelengths for the plurality of semiconductor lasers and for setting heights of the diffraction gratings which provide an identical coupling coefficient independently of the oscillation wavelengths. The coating is etched in such a manner that the level of etching per unit time is identical. A stripe mask is patterned according to the arrangement of the diffraction gratings. A laser active layer is formed on each of the diffraction gratings by selective MOVPE growth. An electrode is formed on each of the laser active layer on its top surface and the backside of the substrate. By virtue of this constitution, an optical semiconductor device and a process for producing the same can be realized which, when a plurality of semiconductor lasers are simultaneously formed on a single semiconductor substrate, can prevent a variation in coupling coefficient.
1. A process for producing an optical semiconductor device comprising a plurality of a semiconductor lasers which oscillate longitudinal single mode laser beams with different wavelengths and have been simultaneously formed on a single substrate, said process comprising the steps of:
coating a resist on the substrate;
exposing the surface of the resist to form a pattern of a plurality of diffraction gratings, said pattern set to a predetermined shape for setting pitches corresponding respectively to oscillation wavelengths for the plurality of semiconductor lasers and for setting each diffraction grating heights to provide a substantially similar coupling coefficient for each laser independently of the oscillation wavelength of each laser;
etching the substrate in such a manner that the level of etching per unit time is identical;
patterning a mask to give a predetermined shape according to the arrangement of the diffraction gratings;
forming a laser active layer on each of the diffraction gratings using the mask having a predetermined shape by a selective MOVPE growth method (metal-organic vapor phase epitaxy); and
forming an electrode on each of the top surface of the laser active layer and the backside of the substrate.
2. The processing according to claim 1 , wherein the height of the diffraction grating is increased for a laser having a smaller coupling coefficient than a predetermined coupling coefficient when the diffraction grating is unchanged.
3. The process according to claim 1 , wherein the height of the diffraction grating is set by the opening width of the resist.
4. The process according to claim 1 , wherein an opening width of the resist is decreased for a laser having a smaller coupling coefficient than a predetermined coupling coefficient when the diffraction grating is unchanged.
5. The process according to claim 1 , wherein
the patterning to give a predetermined shape involves patterning of electro-absorption optical modulators coupled respective to the semiconductors lasers, and
the selective MOVPE growth involves selective MOVPE growth for the formation of an absorption layer in the electro-absorption optical modulator.
6. The process according to claim 1 , wherein the coupling coefficient of the diffraction grating is set by varying the opening width of the resist.