Self-aligned metal-contact and passivation technique for submicron ridge waveguide laser fabrication

One challenge in fabricating submicron ridge waveguide photonic devices is the formation of metal contacts and passivation. In this article, the authors report a self-aligned metal-contact and passivation technique suitable for submicron to nanoscale ridge waveguide device fabrication. The technique uses two different dielectric materials, e.g., SiO2 and Si3N4, with a different wet-etching selectivity. The first dielectric material (SiO2) acts as the etching mask and the second dielectric material (Si3N4) with a much lower etching rate acts as the passivation film. An undercut is formed in the semiconductor below the SiO2 mask by a wet-etching process. The semiconductor surface on top of the ridge waveguide will be fully exposed to metal contact by the lift-off process. A 0.7-mu m-wide InGaAsP/InP ridge waveguide laser was fabricated using the technique proposed. Mode simulation showed that the 0.7-mu m-wide and 1.2-mu m-deep ridge waveguide in the InGaAsP/InP laser structure has good optical field confinement. Lasing is obtained on the 0.7-mu m-wide ridge waveguide laser under current injection. An similar to 240 nm ridge waveguide is also demonstrated as an example of the technology for deep-submicron waveguide structure fabrication. The whole process is completely compatible with the existing compound semiconductor process and can be extended to fabricating other submicron to nanoscale devices. (C) 2008 American Vacuum Society.