Effect of O : Er concentration ratio on the structural, electrical, and optical properties of Si : Er : O layers grown by molecular beam epitaxy

The structural, electrical, and optical properties of crystalline Si codoped with Er and O by molecular beam epitaxy (MBE) have been investigated in detail. Si:Er:O layers (similar to 250 nm thick) have been grown by MBE, realizing uniform dopant concentrations in the range 8 x 10(18)-1.5 x 10(20) cm(-3) for Er and up to 5 x 10(20) cm(-3) for O. The O:Er ratio was varied between 0 and similar to 20. Samples have been subsequently annealed at 900 degrees C for 1 h. We observed that clear constraints to the Er and O contents exist in order to incorporate them in a good quality single crystal. We also found that the O:Er ratio represents the main parameter in determining the properties of this system. For instance, Er is observed to behave as a donor in MBE grown samples and the donor concentration increases with the O:Er ratio until a saturation regime is achieved for a ratio higher than 6-8. All the samples emit light at 1.54 mu m and similar behavior is also found for the optical activation of the Er ions. The thermal process usually increases the number of light emitting Er ions which is also increased by increasing the O:Er ratio; however, for O:Er ratios higher than 6-8, no further activation is measured. In contrast, the most intense room temperature photoluminescence (PL) peak is obtained in samples having an O:Er ratio similar to 2, for which PL temperature quenching is strongly reduced. Indeed, the coupling of these observations with structural measurements allows us to clearly identify the best conditions for an MBE grown Si:Er:O sample. These phenomena are investigated in detail and discussed.