Thermal-assisted contactless photoelectrochemical etching for GaN

Advanced contactless photoelectrochemical etching for GaN was conducted under the condition that the sulfate radicals (SO4-) as the oxidizing agent were mainly produced from the S2O82- ions by heat. The generation rate of SO4- was determined from the titration curve of the pH in the mixed solutions between KOH (aq.) and K2S2O8 (aq.); it clearly increased with an increase in the S2O82- ion concentration. The highest etching rate of >25 nm min(-1) was obtained in the "alkali-free" electrolyte of 0.25 mol dm(-3) (NH4)(2)S2O8 (aq.) at 80 degrees C, which was approximately 10 times higher than that reported by previous studies.