  A major challenge for the next generation of spintronics devices is the
implementation of ferromagnetic-semiconductor thin films as spin injectors and
detectors. Spin-polarised carrier injection cannot be accomplished efficiently
from metals, and coupled with the rarity of intrinsic ferromagnetic
semiconductors this has driven intensive study of diluted magnetic
semiconductors. Chief among these is the doped III-V compound (Ga,Mn)As. These
materials suffer from a number of drawbacks; they (i) require magnetic-ion
doping well above the solubility limit, and (ii) must be hole doped to above
the degenerate limit, preventing independent control of the carrier
concentration and charge sign. Here we demonstrate the first epitaxial growth
of a recently-characterised intrinsic ferromagnetic semiconductor, GdN, on
silicon substrates, providing an essential step on the way to integrate new
spintronics functionalities into Si-based technology. The films have been
characterised as regards their growth toward fully relaxed GdN, the density and
mobility of their carriers, and their magnetic behaviour.
