Fabrication of air bridges on (100) β-Ga2O3 using crystallographic HCl gas etching

β-Ga2O3 air bridges on (100) substrates were fabricated through a self-aligning process that used conventional anisotropic BCl3/Ar-plasma etching and crystallographic plasma-free HCl gas etching. The former etching can be done as vertical etching to expose the etched sidewalls, whereas the latter etching enables horizontal etching that is aligned with the (100) plane owing to the high etch resistance due to the lowest surface energy density of the (100) plane. By combining the two orthogonal etching techniques with other standard device fabrication processes, we were able to create air bridges. We believe that the undercut etching method demonstrated herein will facilitate the fabrication of micro-electromechanical systems.