Ion implantation and cluster formation in silica

Cathodoluminescence (CL), scanning transmission electron microscopy (STEM), and energy dispersive X-ray analysis (EDX) have been used to investigate Si and Ge cluster formation in amorphous silicon dioxide layers and their respective luminescence behavior. Commonly, CL emission spectra of pure SiO2 are identified with particular defect centers within the atomic network of silica including the non-bridging oxygen-hole center (NBOHC) associated with the red luminescence (R) at 650 nm (1.9 eV) and the oxygen deficient centers (ODC) with the blue (13) (460 nm; 2.7 eV) and ultraviolet UV (295 nm; 4.2 eV) bands. In Ge+ ion implanted SiO2 an additional violet (V) Ge related emission band is identified at (410 nm; 3.1 eV). A post-implantation thermal annealing at temperatures T-a = 700-1100 degrees C in dry nitrogen leads up to 900 degrees C to a huge increase of the violet luminescence, followed by a decrease towards 1100 degrees C. The strong increase of the violet luminescence is associated with formation of low-dimension Ge aggregates like dimers, trimers and higher formations; the following decay of luminescence is due to further growing to Ge nanoclusters. (C) 2008 Elsevier Ltd. All rights reserved.