Non-Equilibrium Segregation and Trapping Phenomena during Ion- Induced Crystallization of Amorphous Si.

The segregation and trapping of Au at the moving amorphous- crystal Si interface has been measured. Epitaxial crystallization was induced in the temperature range 250-420C using 2.5 MeV Ar ion irradiation. The interface motion and segregation profiles have been measured directly at intermediate stages during the regrowth using Rutherford backscattering. The Au segregation is analogous to behavior at liquid/solid interfaces. In contrast to the liquid/solid case, the interfacial segregation coefficient of 0.007 at 320C is independent of velocity between 0.6 and 6 angstrom/sec. This process results in the trapping of Au in crystalline Si at concentrations eight orders of magnitude in excess of equilibrium concentration. Similarities between this solid-phase regime and rapid solidification experiments are discussed.