Cathodoluminescence of Ge⁺, Si⁺, and O⁺ implanted SiO₂ layers and the role of mobile oxygen in defect transformations

Thermally grown SiO₂ layers of thickness d = 500 nm have been implanted by Ge⁺, Si⁺, and O⁺ ions of energy 350, 150, and 100 keV, respectively, and a uniform implantation dose of D_i = 5 × 10¹⁶ ions/cm². Thus the implantation profiles are expected with a concentration maximum of nearly 4 at.% at the half-depth d_m ≅ 250 nm of the SiO₂ layers. After thermal annealing to 900 °C for 1 h in dry nitrogen or vacuum the typical violet luminescence band (λ = 400 nm) of the Ge⁺ implanted centers is increased more than 200-fold and the Ge luminescent center depth profile is shifted from about 250 to 170 nm towards the surface as determined by cathodoluminescence (CL) depth profiling. Implanting oxygen increases the red band (λ = 650 nm) but does not affect the blue band (λ = 460 nm). Silicon surplus increases the amplitude of the blue (B) luminescence, but reduces the amplitude of the red (R) one. Studying the irradiation dose dependence of these blue and red bands we have established defect kinetics in SiO₂ including six main defects and precursors, including the non-bridging oxygen hole center for the red luminescence, the twofold-coordinated silicon as the oxygen deficient center ODC(2) for the blue luminescence and the mobile oxygen as the main transmitter between precursors and the radiation induced defects. The kinetics are described by a set of eight differential equations which predict the dose dependence of the CL.