Electrochemical etching of $p$–$n$-GaN/AlGaN photoelectrodes

Specific features of etching of GaN/AlGaN $p$–$n$ structures in a KOH-based electrolyte have been studied. It was found that the corrosion process first passes across $p$ layers through vertical channels associated with threading structural defects. Then, the corrosion process occurs in the lateral direction along $n$ layers of the structure, with local hollows and voids thereby formed. The lateral etching is due to the presence of positive piezoelectric charges at boundaries of $n$-AlGaN and $n$-GaN layers and positively charged ionized donors in the space-charge region of the $p$–$n$ junction.