Pre-irradiation memory effect on the photoluminescence intensity of Ge-implanted SiO_2 layers

摘要

180 nm thick SiO_2 layers thermally grown on crystalline Si were irradiated with He~+, Si~+, Kr~(++) and Au~+ ions transferring different amounts of electronic (S_c) and nuclear (S_n) energy to the film. After the irradiation, the SiO_2 layers were implanted with 120 keV Ge~+ ions at a fluence of 1.2 x 10~(16) cm~(-2). Thermal annealings in the 400-800℃ temperature range were performed to allow the formation of Ge-nanoclusters, characterized by transmission electron microscopy. The photoluminescence (PL) properties of the pre-irradiated Ge-implanted layers were investigated and compared with those from non-pre-irradiated samples. The results showed that, in both situations, PL emissions are observed in the blue-violet and ultra-violet spectral regions. At 800℃ the blue-violet PL intensity of the Ge-implanted layer pre-irradiated with Si~+ ions is about 65% higher than in the non-pre-irradiated Ge-implanted layer while for the Au-irradiated layer a decrease by a factor of ≈6 was observed. Furthermore, we also observe that the mean cluster sizes are affected by the pre-irradiation. These data indicate a pre-irradiation memory effect on the PL intensity and on the cluster growth. The results are discussed in terms of a new model correlating the formation of PL luminescence centers with the cluster coarsening behavior.