A comparative study of photoenhanced wet chemical etching and reactive ion etching of GaN epilayers grown on various substrates

We have explored wet and dry etching of GaN epilayers using photoenhanced wet etching and reactive ion etching. Samples investigated were commercially grown by hydride vapour phase epitaxy (HVPE) on SiC and sapphire substrates. Aqueous KOH was used for an electrolyte and UV illumination from a xenon lamp for photoenhanced wet etching. For reactive ion etching, we used a gas mixture of CCl₂F₂ and argon. Typical etch rates measured were 40 nm/min and 20 nm/min for wet and dry etching respectively. We found that post wet-etched surfaces were very rough compared with dry etched surfaces. Both techniques were found to reveal the defects in the epilayers and reactive ion etching revealed etch pits in the GaN/Al₂O₃ samples. Etch pit density was found to increase slightly as etch time progressed and after 30 minutes, the density was 1×10⁸ /cm². After 90 minutes etching, the substrate was revealed and no etch pits were observed