Proton-implantation-induced optical phenomena in SiO₂:GeO₂ glasses: Formation of photosensitive defects and nanometer sized Ge crystals

Ion implantation of 1.5 MeV protons to 1GeO₂-9SiO₂ glasses induces interesting phenomena. For a fluence 1 × 10¹⁷ cm^-2, oxygen-deficient type point defects associated with Ge ions were primarily formed, and for fluences > 5 × 10¹⁷ cm^-2 the formation of Ge fine crystalline particles was observed. Nanometer-sized crystalline Ge colloid particles were formed by implantation of protons at 1.5 MeV without post-thermal annealing. The depth of colloid formation layers from the implanted surface agreed with the peak region of electronic energy deposition. No formation of Ge colloids and the Ge related oxygen point defects were noted for implantation of 1.5 MeV He⁺ to a fluence of 1 × 10¹⁸ cm^-2. A tentative mechanism for the Ge nanocrystal formation is proposed.