Photochemical metallization for GaAs

Abstract

Metal-semiconductor junctions are important elements in semiconductor devices. An ohmic contact can be formed to provide better conductivity for the device. In order to improve traditional metal screen printing, which is fast and low cost but has a high resistance, a new metallization process is being developed. In this project, we performed an experiment on photochemical metal etching for selective area liftoff. Photochemical etching is a process using light and a chemical solution to create a pattern onto the substrate. A GaAs substrate coated with a thin layer of nickel is etched in an HCl solution under light illumination. We demonstrate that selective areas of a substrate can be metallized through this etching process if a mask such as a SiNx layer or ink from a permanent marker is used to selectively protect the metal. An alternate approach for metallization is to use light-induced electroplating. Light-induced electroplating is a method to deposit metal from a solution onto another substance in the presence of electrical current and light. A piece of GaAs with an aluminum rear contact and a nickel seed layer is placed in a gold plating bath connected to electrodes and under light illumination. In this thesis, we review methods from the literature for light-induced electroplating and suggest ideas for future experimental work in this area.