Formation of photoluminescence centers during annealing of SiO2 layers implanted with Ge ions

Photoluminescence (PL), Raman scattering, and the Rutherford backscattering of α-particles were used to study the formation of the centers of radiative-recombination emission in the visible region of the spectrum on annealing of the SiO₂ layers implanted with Ge ions. It was found that the Ge-containing centers were formed in the as-implanted layers, whereas the stages of increase and decrease in the intensities of PL bands were observed following an increase in the annealing temperature to 800°C. The diffusion-related redistribution of Ge atoms was observed only when the annealing temperatures were as high as 1000°C and was accompanied by formation of Ge nanocrystals. However, this did not give rise to intense PL as distinct from the case of Si-enriched SiO₂ layers subjected to the same treatment. It is assumed that, prior to the onset of Ge diffusion, the formation of PL centers occurs via completion of direct bonds between the neighboring excess atoms, which gives rise to the dominant violet PL band (similar to the PL of O vacancies in SiO₂) and a low-intensity long-wavelength emission from various Ge-containing complexes. The subsequent formation of centers of PL with λ_m～570 nm as a result of anneals at temperatures below 800°C is explained by agglomeration of bonded Ge atoms with formation of compact nanocrystalline precipitates. The absence of intense PL following the high-temperature anneals is believed to be caused by irregularities in the interfaces between the formed Ge nanoc-rystals and the SiO₂ matrix.