EXAFS analysis of Er sites in Er-O and Er-F co-doped crystalline Si

We present extended X-ray absorption fine structure (EXAFS) and photoluminescence (PL) analyses of Er-O and Er-F co-doped Si. Samples were prepared by multiple implants at 77 K of Er and co-dopant (O or F) ions resulting in the formation of a congruent to 2 mu m thick amorphous layer uniformly doped with 1 x 10(19) Er/cm(3) and 3 x 10(19) O/cm(3), 1 x 10(20) O/cm(3) or 1 x 10(20) F/cm(3). EXAFS measurements show that the local environment of the Er sites in the amorphous layers consists of 6 Si first neighbors. After epitaxial regrowth at 620 degrees C for 3 h, Er is fully coordinated with 8 F ions in the Er-F samples, while Si and O ions are concomitantly present in the first shell of O co-doped samples. Post regrowth thermal treatments at 900 degrees C leave the coordination unchanged in the Er + F, while the Er + O (ratio 1: 10) doped samples present Er sites with a fully O coordinated shell with an average of 5 O atoms and 4 O atoms after 30 s and 12 h, respectively. We have also found that the fine structure and intensity of the high-resolution PL spectra are strongly dependent on the Er-impurity ratio and on thermal process parameters in the Er-O co-doped samples, while this is not observed for the F-doped samples. The most intense PL response at 15 K was obtained for the 1 : 3 E : O ratio, suggesting that an incomplete O shell around Er is particularly suitable for optical excitation,