Yields and energy distributions of sputtered semiconductor clusters

Abstract

We have investigated the formation of clusters during sputtering of a germanium surface by 5-keV Ar + ions impinging under 45 ∘ with respect to the surface normal. Charged clusters were detected directly by time-of-flight mass spectrometry (TOF-MS), the corresponding neutral species were post-ionized prior to mass and energy analysis by means of single photon ionization from an intense VUV laser beam. It is shown that the photoionization process can be saturated without indication of significant photofragmentation of the clusters. The relative yields of sputtered Ge n clusters are found to obey a power law dependence on the cluster size n with an exponent around −6.5. The kinetic energy distributions exhibit a shift of the maximum towards lower energies with increasing cluster size, the asymptotic decay towards high energies is found to be virtually identical for all measured atoms and clusters. The experiments were repeated on two different single crystalline Ge surfaces (〈1 0 0〉 and〈1 1 1〉) which could be reproducibly amorphized by ion bombardment and re-annealed. As a result, it is found that the crystalline structure of the ion bombarded surface does not play a significant role in the formation of sputtered clusters.