Capping-induced suppression of annealing effects on Ga1−xMnxAs epilayers

We have studied the effects of capping ferromagnetic Ga1−xMnxAs 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 Ga1−xMnxAs epilayer strongly affects the defect structure, has important implications for the incorporation of Ga1−xMnxAs into device heterostructures.