Enhanced formation of Ge nanocrystals in Ge:SiO ₂ layers by swift heavy ions

In this paper we report the ability of swift heavy Xe ions with an energy of 480MeV and a fluence of 10 ¹²cm ² to enhance the formation of Ge nanocrystals within SiO ₂ layers with variable Ge contents. These Ge-SiO ₂ films were fabricated by the co-sputtering of Ge and quartz sources which followed various annealing procedures. In particular, we found that the irradiation of the Ge:SiO ₂ films with subsequent annealing at 500°C leads to the formation of a high concentration of nanocrystals (NCs) with a size of 2-5nm, whereas without irradiation only amorphous inclusions were observed. This effect, as evidenced by Raman spectra, is enhanced by pre-irradiation at 550°C and post-irradiation annealing at 600°C, which also leads to the observation of room temperature visible photoluminescence.