Growth over grating in 1.5 μm DFB lasers

Growth over grating is an important process step in determining the performance of DFB lasers. While destructive methods such as SEM can be used to assess the regrowth step and preservation of the grating, nondestructive means are desirable for process monitoring. In this work, we demonstrate how the grating overgrowth quality can be evaluated by measuring the photoluminescence efficiency (PLE) of the MQW active stack grown on top of these layers. In addition, the use of the peak photoluminescence (PL) intensity of the InGaAs layers can be used to determine the degree of grating preservation. The combination of these two measurements provides a non-destructive means to assess the overall quality of the regrowth, and has been used to determine the optimal growth conditions to maximize both MQW PL efficiency and grating preservation