Sputtering and etching of GaN surfaces

Sputtering of the GaN(0001) surface by Ar⁺ and N₂⁺ ion beams is investigated using synchrotron-radiation photoemission spectroscopy. For Ar⁺ sputtering, the N atom is preferentially removed and a Ga-enriched GaN surface is produced. The excess Ga atoms on the Ar⁺-sputtered surface aggregate to form metallic Ga clusters at temperatures above 623 K. A better-ordered GaN(0001)-1 × 1 surface can be obtained by N₂⁺ sputtering, instead of Ar⁺ sputtering. In addition to acting as a sputtering particle, the N₂⁺ ion also serves as a reactant which compensates for the preferential loss of the N atom caused by physical ion bombardment. During chlorination of GaN, chlorine preferentially reacts with surface Ga atoms to form Ga chlorides. Although Ga monochloride (GaCl) is the major product formed on the N₂⁺-sputtered surface, however, volatile chlorides (GaCl₂ and GaCl₃) are mainly produced on the Ar⁺-sputtered surface. The formation of volatile products on the Ar⁺-sputtered GaN surface may result in higher etching rates and lower etching temperatures for ionassisted chemical etching.