The design and the fabrication of monolithically integrated GaInAsP MQW laser with butt-coupled waveguide

We optimized the etching process for butt coupling to improve the reproducibility and the uniformity of the process for the integrated GaInAsP multiquantum-well laser with a butt-coupled waveguide. Three different ways of etching process were tested, which are reactive ion etching (RIE), RIE followed by a small amount (50 nm thick) of selective wet etching, and RIE followed by an adequate amount (125 nm thick) of selective wet etching. RIE followed by an adequate amount of selective wet etching showed the superior properties to the common expectation on RIE only, giving the measured coupling efficiency 96+-1.7% versus 34+8%. The high coupling efficiency and the very small variation across a quarter of a 2-in wafer demonstrate that RIE coupled with an adequate amount of selective wet etching can also replace the conventional process for butt coupling, RIE followed by HBr-based nonselective wet etching, to fabricate highquality integrated photonic devices.