Highly reproducible and defect-free MOVPE overgrowth of InGaAsP-based DFB gratings

The paper reports on a study aiming to develop a highly reproducible process for the MOVPE overgrowth of first-order gratings made by reactive ion etching in InGaAsP. MOVPE parameters were elaborated, which guarantee both nearly perfect preservation of the gratings and an almost defect-free surface of the regrown InP layer. Whereas the former goal calls for a low growth temperature, the latter was found to be achievable only above a critical growth temperature depending on the growth rate adjusted. As a good compromise, a regrowth starting temperature of 550 degrees C and an extremely high V/III ratio in the initial stage of regrowth have been chosen. Furthermore, a well-adjusted concentration of AsH3 has been added during the heat-up cycle.