Epitaxial growth and magnetic properties of a new group-Ⅳ ferromagnetic semiconductor: Ge_(1-x)Fe_x

摘要

Epitaxial growth and magnetic properties of group-Ⅳ ferromagnetic semiconductor Ge_(1-x)Fe_x thin films were investigated by employing in-situ reflection high-energy electron diffraction (RHEED), transmission electron microscopy (TEM), and magnetic circular dichroism (MCD). When Ge_(1-x)Fe_x films were grown at substrate temperatures (T_S) of 100-200℃, their RHEED pattern showed streaks with a 2x2 reconstruction pattern, indicating two-dimensional growth mode with atomically flat surface morphology. Single-phase crystallographic structure without Fe-Ge intermetallic compounds was observed in the films by TEM. MCD measurements revealed that s,p-d exchange interactions induced by the incorporation of Fe atoms that occupied the substitutional sites of the host Ge matrix cause single-phase ferromagnetic ordering in the Ge_(1-x)Fe_x films. Above T_S = 300℃, the growth mode was changed from two-dimensional growth mode to three-dimensional growth mode. It was found from MCD observations that when Ge_(1-x)Fe_x films are grown at T_S = 300-400℃, phase separation occurs and the films contain ferromagnetic precipitates. A ferromagnetic semiconductor phase was obtained for T_S ranging from 100℃ to 200℃, and higher Curie temperature was obtained for T_S = 200℃.