Thermal stability of interstitial and substitutional Mn in ferromagnetic (Ga,Mn)As

In (Ga,Mn)As, a model dilute magnetic semiconductor, the electric and magnetic properties are strongly influenced by the lattice sites occupied by the Mn atoms. In particular, the highest Curie temperatures are achieved upon thermal annealing in a narrow temperature window around $200{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$, by promoting the diffusion of interstitial Mn towards the surface. In this work, we determined the thermal stability of both interstitial and substitutional Mn in ferromagnetic (Ga,Mn)As thin films, using the emission channeling technique. At a higher Mn concentration, the temperatures at which substitutional and interstitial Mn become mobile not only decrease, but also become closer to each other. These findings advance our understanding of self-compensation in (Ga,Mn)As by showing that the strong dependence of the Curie temperature on annealing temperature around $200{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$ is a consequence of balance between diffusion of interstitial Mn and segregation of substitutional Mn.