Surface roughness-controlled foam-like GaN fabricated by the change H2O concentration in ionic liquid etchant solution via photoelectrochemical etching

The structure and morphology of foam-like GaN (F-GaN) was significant to the performances of nanodevices, especially optoelectronic devices. Here we present a reasonable way to regulate the surface roughness on F-GaN, by the change of H2O concentration in the etching system. Ionic liquid (ILs) 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([EMIM][OTF]) was used as the etchant for the photoelectrochemical etching (PECE) process. With the H2O concentration changed from 0 to 5 % in the etchant solution, the surface roughness of FGaN was reduced from 57.6 to 34.6 nm. In addition, to describe the role of H2O in the etching procedure, a physical impact etching mechanism was proposed. These results further promoted the potential value of F-GaN in the optical field.