  We study the growth and properties of quaternary-alloy ferromagnetic
semiconductor (FMS) (In0.94-x,Gax,Fe0.06)Sb (x = 5% - 30%, Fe concentration is
fixed at 6%) grown by low temperature molecular beam epitaxy
(LT-MBE).Reflection high-energy electron diffraction (RHEED) patterns, scanning
transmission electron microscopy (STEM) lattice images, and X-ray diffraction
(XRD) spectra indicate that the (In0.94-x,Gax,Fe0.06)Sb layers have a
zinc-blende crystal structure without any other second phase. The lattice
constant of the (In0.94-x,Gax,Fe0.06)Sb films changes linearly with the Ga
concentration x, indicating that Ga atoms substitute In atoms in the zinc-blend
structure. We found that the carrier type of can be systematically controlled
by varying x, being n-type when x \le 10% and p-type when x \ge 20%.
Characterizations using magnetic circular dichroism (MCD) spectroscopy indicate
that the (In0.94-x,Gax,Fe0.06)Sb layers have intrinsic ferromagnetism with
relatively high Curie temperatures (TC = 40 - 120 K). The ability to widely
control the fundamental material properties (lattice constant, bandgap, carrier
type, magnetic property) of (In0.94-x,Gax,Fe0.06)Sb demonstrated in this work
is essential for spintronic device applications.
