Effect of film thickness on the incorporation of Mn interstitiels in Ga 1-xMn xas

We have investigated the effect of film thickness on the distribution of Mn atoms at various lattice sites in Ga _1-xMn _xAs thin films. We find that the growth surface acts as a sink facilitating the outdiffusion of Mn interstitiels (Mn _I), and thus reducing its concentration in the film. The outdiffused Mn _I accumulate on the surface in a surface oxide layer and do not participate in the ferromagnetism of the film. For thin films less than 15 nm thick, no Mn _I can be detected. Because of the absence of compensating Mn _I defects, higher T _C can be achieved for such extremely thin Ga _1-xMn _xAs layers. These results agree with our previously suggested Fermi-level-governed upper limit of the T _C of III-Mn-V ferromagnetic semiconductors. © 2005 American Institute of Physics.