Quantitative investigation of the O₂⁺‐induced topography of GaAs and other III–V semiconductors: An STM study of the ripple formation and suppression of the secondary ion yield change by sample rotation

Abstract

Roughening procedures including the early stage of the O,+-induced ripple formation of GaAs were studied quantitatively by scanning tunnelling microscopy (STM). Detailed examinations of the beginning of topography develop ment using fast Fourier transform of the STM images revealed that the ripple formation was not caused by any accidental defects, particles or original irregularity on the substrate, but solely by the conditions of the ion b e a m A systematic investigation of the rippled GaAs surface produced under various 0,' bombardment conditioas was conducted. The ripple wavelength and the transition depth were almost exactly proportional to E,.cos 0, where Ep and 8 are the energy of the ion beam and the incident angle, respectively. For GaAs, the secondary ion yield transition occurs when the slope of ripples facing the incident'0,' beam reaches a saturation angle of 20-30" from the macroscopic surface plane. Topography change on other 111-V semiconductors was also examined for comparison. There was no ripple generation observed for Gap; InP gave a ripple-like structure without secondary ion yield change. A relatively rough surface resulted on GaSb and InAs at a much shallower depth than for GaAs. Rippling and ion yield changes during depth profiling have been suppressed successfully by sample rotation even in a magnetic sector-based instrument.

Morphology of ion-sputtered surfaces

“…These results were corroborated by Karen et al [8][9][10], who investigated ripple formation on GaAs surfaces under bombardment with 10.5 keV O + 2 ions. They found that ripple formation takes place for angles of incidence between 30…”

“…[8][9][10]. The experiments indicate that the ripple wavelength is linear in the energy, following ℓ ∼ ǫ cos θ.…”

“…Furthermore, in Refs. [8][9][10] it was unambiguously shown that the process of ripple formation is not caused by defects or inherited irregularities on the surface, but is determined merely by the primary ion characteristics. These results indicate that ripple formation is independent of microscopic details and the surface chemistry.…”

Wavelength tunability of ion-bombardment-induced ripples on sapphire

“…The sapphire ripple wavelength increases with ion energy at low temperature, which is consistent with observations for ion eroded SiO 2 , GaAs and Si surfaces. 19,24,25 The data obtained from high/low flux ion sources overlap within experimental error at both 500 eV and 1000 eV, which indicates that the ripple wavelength is independent of incident ion flux at low temperature. A non-linear least squares fit gives a power law coefficient with p=0.71 for the dependence of the wavelength on ion energy (ℓ x ∼ ε p ).…”

Energy dependence of quantum dot formation by ion sputtering

“…Careful calculations of the energy distribution by molecular-dynamic simulations are necessary to clarify to what extent is underestimated by TRIM. For oblique incidence ion sputtering the energy dependence of the characteristic wavelength has been investigated by several groups. 6,27 Theoretically the characteristic wavelength is obtained from the more complicated anisotropic KS equation, which makes the results more sensitive to specific parameter differences than under isotropic sputtering conditions. e.g., Vajo et al investigated the energy dependence of the characteristic wavelength for Si ͑100͒ surfaces in the energy range of 1.5 to 7 keV.…”