Thermodynamical limits of diluted magnetic semiconductors

The incorporation of transition metals dopants in semiconductors over their solubility limit is the main challenge for the fabrication of diluted ferromagnetic semiconductors. Dietl et al. [1] calculated the Curie temperatures for various semiconductors doped with 5 at% Mn. A lot of experimental effort was focused on the fabrication of diluted magnetic semiconductors. Unfortunately, such metastable alloys try to reach their thermodynamical equilibrium by the diffusion of the incorporated dopants. The equilibrium state at room temperature for semiconductors with a low solubility of magnetic dopant atoms is characterized by unwanted secondary phases. We present the results from combined random walk simulations and heatflow calculations and explain the successful fabrication of GaAs:Mn and the impossibility to produce Si:Mn. The clustering process is simulated under the assumption that neighbouring magnetic atoms stick together. This is a general approach for the growth of clusters in supersaturated materials [2]. With the knowledge of the diffusion coefficient our modelling can be used to predict the thermodynamical limit at room temperature and the producibility by pulsed laser annealing of diluted magnetic semiconductors.
[1] T. Dietl, H. Ohno, F. Matsukura, J. Cibert, and D. Ferrand, Science 287, 1019 (2000)
[2] P. Meakin, Fractals, scaling and growth far from equilibrium (Cambridge University Press, 1998)