Segregation and trapping of erbium at a moving crystal-amorphous Si interface

Segregation and trapping of Er during solid-phase crystallization of amorphous Si on crystalline Si is studied in a concentration range of 10¹⁶-5×10²⁰ Er/cm³. Amorphous surface layers are prepared on Si(100) by 250 keV Er ion implantation, recrystallized at 600 °C, and then analyzed using high-resolution Rutherford backscattering spectrometry using 2 MeV He⁺ or 100 keV H⁺. The segregation coefficient k depends strongly on Er concentration. At Er interface areal densities below 6×10¹³ Er/cm² nearly full segregation to the surface is observed, with k=0.01. At higher Er densities, segregation and trapping in the crystal are observed, with k=0.20. The results are consistent with a model in which it is assumed that defects in the a-Si near the interface act as traps for the Er.