Laser/waveguide integration utilizing selective area MOMBE regrowth for photonic IC applications

The potential of metal organic MBE for selective deposition of InP/GaInAsP passive optical waveguide structures was studied for butt coupling with an active laser waveguide. By use of appropriate ex-situ and in-situ preparation procedures of the masked laser surfaces and high V/III ratios during regrowth virtually ideal butt-joints without any significant deterioration of the topography near the lateral interface and minimum lateral separation between the active and the passive waveguide were achieved. In addition, besides the absence of gas phase pre-reactions during MOMBE, careful ex-situ surface cleaning helped to reduce the growth temperature to as low as 485 degrees C without loss of selectivity. Such a low deposition temperature results in suppression of dopant movement during growth of semi-insulating Fe doped waveguides. SIMS measurements revealed laterally homogeneous incorporation behaviour of the Fe dopant in the waveguide layers without any accumulation at the lateral laser/waveguide interface as well as any detectable Fe indiffusion into the laser region. Device quality of the deposition process was evaluated from the characteristics of Fabry-Perot lasers comprising an active and a passive waveguide section. Only a small increase of the threshold current by some 30% for a 600 mu m long passive section as compared to a bare laser demonstrates the applicability of the fabricated butt-joint in photonic ICs. Butt coupling efficiencies of(62+or-12)% for 3 mu m wide structures have been determined from measuring the threshold current as function of the passive waveguide length.