A STUDY OF THE SECONDARY-ION YIELD CHANGE ON THE GAAS SURFACE CAUSED BY THE O2+ ION-BEAM-INDUCED RIPPLING

The oxygen ion-beam-induced ripples observed during depth profiling of the GaAs surface by secondary-ion mass spectrometry has been studied by scanning tunneling microscopy. Under the O2+ primary-ion bombardment with energy of 10.5 kV at an incident angle of 37-degrees, ripples of wavelength of 230 nm with the ridge lines perpendicular to the beam direction are formed, and they are grown to approximately 80 nm in amplitude on the sputtered surface. Secondary-ion intensity changes abruptly in accordance with the development of ripples when they reach an amplitude of 30-50 nm. The phenomenon occurs only when the primary beam direction is perpendicular to the ridge orientation. It suggests that the ion yield enhancement is effected by increase of local concentration of oxygen implanted onto the rippled surface. Dependence of the enhancement on sputtered elements also seems to agree with the proposed mechanism.