  We grow Fe film on (4 by 2)-GaAs(100) at low temperature, (~ 130 K) and study
their chemical structure by photoelectron spectroscopy using synchrotron
radiation. We observe the effective suppression of As segregation and
remarkable reduction of alloy formation near the interface between Fe and
substrate. Hence, this should be a way to grow virtually pristine Fe film on
GaAs(100). Further, the Fe film is found stable against As segregation even
after warmed up to room temperature. There only forms very thin, ~ 8 angstrom
thick interface alloy. It is speculated that the interface alloy forms via
surface diffusion mediated by interface defects formed during the low
temperature growth of the Fe film. Further out-diffusion of both Ga and As are
suppressed because it should then proceed via inefficient bulk diffusion.
