Fabrication of Bragg Gratings Using Interferometric Lithography
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A setup has been designed and realized for the fabrication of Bragg Gratings in edge emitting semiconductor laser. In this setup a HeCd laser, at 325nm, is used in a Lloyd's mirror configuration, to interferometrically expose a sinusoidal grating on photoresist. The dilution of photo-resistant (PR) material allows for a spincoat thickness of 50nm which is needed to minimize standing waves in the photo-resist that lead to a nonuniform exposure. Variations of exposure time show the progression of photo-resist gratings. Etching recipes using both dry and wet etching techniques were successfully used to transfer the grating pattern into semiconductor material. Bragg Gratings with period of 250nm in InP and InGaAs have been characterized with an Atomic Force Microscope to have a grating height of over 100nm.