Bilayer-by-bilayer etching of 6H-GaN(0 0 0 1) with Cl

Etching of Ga-polar GaN(0 0 0 1) surface with Cl has been studied using scanning tunneling microscopy. Three different processes in the thermally activated Cl reaction, i.e., the removal of Ga-fluid, the formation of alternative zigzag and smooth steps, and the initiation of triangle pits on the terrace that take place at different temperatures, are identified. The atom removal is found to proceed via a bilayer-by-bilayer mode on the GaN surface, and the underlying mechanism is discussed in terms of the surface atomic structure.