  We have studied the effects of capping ferromagnetic Ga(1-x)Mn(x)As epilayers
with a thin layer of undoped GaAs, and we find that even a few monolayers of
GaAs have a significant effect on the ferromagnetic properties. In particular,
the presence of a capping layer only 10 monolayers thick completely suppresses
the enhancement of the ferromagnetism associated with low temperature
annealing. This result, which demonstrates that the surface of a Ga(1-x)Mn(x)As
epilayer strongly affects the defect structure, has important implications for
the incorporation of Ga(1-x)Mn(x)As into device heterostructures.
