Fluence dependence of the surface roughness of InP after N2+ bombardment

InP(1 0 0) surfaces were sputtered under ultrahigh vacuum conditions by 5 keV N2+ ions at an angle of incidence of 41° to the sample normal. The fluence, ϕ, used in this study, varied from 1 × 1014 to 5 × 1018 N2+ cm−2. The surface topography was investigated using field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). At the lower fluences (ϕ ⩽ 5 × 1016 N2+ cm−2) only conelike features appeared, similar in shape as was found for noble gas ion bombardment of InP. At the higher fluences, ripples also appeared on the surface. The bombardment-induced topography was quantified using the rms roughness. This parameter showed a linear relationship with the logarithm of the fluence. A model is presented to explain this relationship. The ripple wavelength was also determined using a Fourier transform method. These measurements as a function of fluence do not agree with the predictions of the Bradley-Harper theory.