7 - Porous silicon and germanium thin layers with silver nanoparticles

Abstract

Recent experiments on fabrication of nanoporous Si and Ge layers with Ag nanoparticles by low-energy high-dose ion implantation are discussed. Ag+-ion implantation of c-Si and c-Ge single-crystals at low-energy (E=30keV) high-doses (D=1.25×1015–1.5×1017 ion/cm2) and current density (J=2–15μA/cm2) was carried out for this purpose. The changes of Si and Ge surface morphology after ion implantation were studied by scanning electron and atomic force microscopy. The near surface area of samples was also analyzed by diffraction of the backscattered electrons and energy-dispersive X-ray microanalysis. Amorphization of the near-surface layer was observed at the lowest implantation doses of c-Si. Ag nanoparticles were synthesized and uniformly distributed over the near Si surface when the threshold dose of 3.1×1015 ion/cm2 exceeded. At a dose of more than 1017 ion/cm2, the formation of a surface nanoporous silicon structure was detected. Ag nanoparticle size distribution function became bimodal and the largest particles were localized along Si-pore walls. In the case of Ge substrates, as a result of the implantation on the c-Ge surface, a porous amorphous PGe layer of a spongy structure was formed consisting of a network of intersecting Ge nanowires with an average diameter of ∼10–20nm. At the ends of the nanowires, the synthesis of Ag nanoparticles was observed. It was found that the formation of pores during Ag+-ion implantation was accompanied by efficient spattering of the Si and Ge surface. Thus, ion implantation is suggested to be used for the formation of nanoporous semiconductor thin layers for industries, which could be easily combined with the crystalline matrix for various applications.