Fabrication of GaN-based Photonic Crystal Structures by Reactive Ion Etching 87 Fabrication of GaN-based Photonic Crystal Structures by Reactive Ion Etching

The fabrication of the 2D GaN-based photonic crystal structure at optical scales, a subμm scale in our case is very challenging. In our work, a double-etching method proved to be feasible to achieve the periodic GaN/air variation. The pattern was defined in a PMMA resist by electron-beam lithography and transferred to SiO2 by reactive ion etching (RIE) in a CF4 plasma and further into GaN by RIE in a chlorine plasma. An interesting phenomenon during RIE was observed: the etching rate at the barrier site is enhanced to about two times of that in the μm scale while the etching rate at the valley site stays the same. If the mask is exhausted during RIE, the etching depth increases before the mask disappearance and decreases after that with further etching. Thus the etching time is a critical parameter to obtain deep enough holes in GaN. Referring to the etching rates of Si3N4 and SiO2 in both kinds of plasma, it might be easier to achieve deep holes when Si3N4 substitutes SiO2.