Smooth and Vertical Sidewall Formation for AlGaN-Based Electronic and Optoelectronic Devices

We report a two-step etching process involving inductively coupled plasma (ICP) etching followed by wet chemical etching to achieve smooth and vertical sidewalls, being beneficial for AlGaN-based electronic and optoelectronic devices. The influence of ICP power on the roughness of etched sidewalls is investigated. It is observed that ICP etching alone does not produce smooth sidewalls, necessitating subsequent wet chemical etching using tetramethyl ammonium hydroxide (TMAH) to enhance sidewall smoothness and reduce tilt angle. The morphological evolution of the etched sidewalls with wet etch time for the device structures is also thoroughly investigated. Consistent etch results are achieved for Al x Ga 1-x N alloys with Al compositions up to 70%, indicating the effectiveness of our etching process.