Optical semiconductor device and process of prodcuing same

An optical semiconductor device, comprising:

• a semiconductor substrate;
• a diffraction grating in the form of a periodic corrugation formed by processing a surface of the semiconductor substrate for selectively transmitting a light having a specific wavelength;
• and
• a guide layer, an active layer and a clad layer formed on the diffraction grating in that order,
• said diffraction grating having a corrugation height determined by the following steps (A) to (D);
• (A) preparing a plurality of reference samples having diffraction gratings with different corrugation heights, respectively, by (1) processing surfaces of a plurality of semiconductor wafers or a plurality of surface regions of a single semiconductor wafer;
• (2) forming on the diffraction gratings a guide layer, an active layer and a clad layer in that order;
• and (3) forming on the clad layer a double heterostructure composed of lower and upper layers, the upper layer having a bandgap greater than that of the active layer;
• (B) measuring the photoluminescence intensity of the lower layers of the double heterostructures of the reference samples;
• (C) determining two ranges of the corrugation height in which the photoluminescence intensity takes higher and lower levels of values, respectively, based on an interrelationship between the measured values of the photoluminescence intensity and the corresponding corrugation heights of the diffraction gratings;
• and
• (D) electing the corrugation height within the determined range in which the photoluminescence intensity takes the higher level of value.