Structural and magnetic properties of epitaxially grown Ge1-xFex thin films:: Fe concentration dependence

Ge1-xFex films (x=2.0%-24.0%) grown by low-temperature molecular beam epitaxy were shown to have a diamond-type crystal structure without any other crystallographic phase of precipitates, although they contain slightly nonuniform Fe distribution and tiny stacking fault defects. The lattice constant decreases linearly with increasing the Fe content x from 0% to 13.0%, and is saturated for x > 13.0%. The Curie temperature (T-C) increases in proportion to x (<= 13.0%) and is saturated for x > 13.0%. The maximum T-C value was similar to 170 K at x > 13.0%. The structural and magnetic properties indicate that Ge1-xFex is an "intrinsic" ferromagnetic semiconductor. (c) 2007 American Institute of Physics.