Tuning the Si(100) surface by Pb to yield high-Curie-temperature Si1-x Mn x with MBE: A first-principles study

A high solubility and site preference for Mn doping in Si are the two keys for realizing high-Curie-temperature ferromagnetism in Si_1-x Mn _x . First-principles calculations reveal that both the substitutional and interstitial Mn are more favored on the Si surface than in bulk, and the substitutional Mn is more favored than the interstitial one on the reconstructed clean Si(100) surface. However, during molecular beam epitaxy, the surface is prone to further reconstructions due to the continuous deposition of feeding species. Neither substitutional nor interstitial Mn is favored, similar to that in Si bulk. Deposition of submonolayer of Pb onto the surface can restore the electronic structure of the clean surface and the favorability of the substitutional Mn, enhancing the Mn incorporation into Si significantly.