The influence of capping layers on pore formation in Ge during ion implantation

Abstract

Ion induced porosity in Ge has been investigated with and without a cap layer for two ion species, Ge and Sn, with respect to ion fluence and temperature. Results without a cap are consistent with a previous work in terms of an observed ion fluence and temperature dependence of porosity, but with a clear ion species effect where heavier Sn ions induce porosity at lower temperature (and fluence) than Ge. The effect of a cap layer is to suppress porosity for both Sn and Ge at lower temperatures but in different temperatures and fluence regimes. At room temperature, a cap does not suppress porosity and results in a more organised pore structure under conditions where sputtering of the underlying Ge does not occur. Finally, we observed an interesting effect in which a barrier layer of aGe that is denuded of pores formed directly below the cap layer. The thickness of this layer ($ 8 nm) is largely independent of ion species, fluence, temperature, and cap material, and we suggest that this is due to viscous flow of aGe under ion irradiation and wetting of the cap layer to minimize the interfacial free energy. Published by AIP Publishing.

Unprecedented severe atomic redistribution in germanium induced by MeV self-irradiation

“…Noticeably, the Ge layer in this study does not develop into a porous structure as observed for an implant at this dose and ion energies of several hundred keV. We have mentioned that porosity in Ge consistently occurs for the implant dose > 2 − 3 • 10 15 cm −2 at room temperature for the medium energy regime [10,13,14] and for the high energy regime [18,19].…”

“…Therefore, the characteristics of the morphology are different at medium energies. Indeed, under ion irradiation at hundreds of keV, Ge shows different modifications from shallow pits [7] to sponge-like structures [8][9][10]. Using a 280 keV 209 Bi ion beam, Appleton et al were the first to report a porosity effect in Ge implanted at the dose of ~4 • 10 15 cm −2 at room temperature [8,11,12].…”

“…Evidently, low substrate temperatures [9,10] and capping layers [10,16] can reduce the surface diffusion and the nucleation of vacancies on the surface, hence effectively suppressing and delaying the porosity up to the implant dose of ~10 17 cm −2 for Ge implants [10] and ~3 • 10 16 cm −2 for Sn implants [16].…”

Suppression of ion-implantation induced porosity in germanium by a silicon dioxide capping layer

“…Above À50 C, the effectiveness of the cap completely diminishes, particularly for heavy implant species such as Sn or Sb. 23 Further investigation of the samples was conducted by using electron microscopy analysis (SEM and TEM) on selected samples of interest. In Fig.…”

“…However, it may be related to the confining effect of the cap in suppressing ion-induced vacancy migration and agglomeration at the surface. 23 Further studies would be needed to resolve this issue.…”