This work investigates reactive ion beam etching processes of GaN in O-2/Ar plasmas and examines the electrical behavior of Schottky diodes fabricated on O-2/Ar plasmas reactive ion beam (RIB) etched samples. To explore the role that the oxygen plasma plays on the etched GaN, photoluminescence and depth-resolved cathodoluminescence are applied to elucidate the defect relative yellow luminescence. The observation of oxygen-content-dependent defects that are associated with the yellow band has important consequences for our understanding of defect-related luminescence in GaN.