Enhancement of ferromagnetism in polycrystalline Si_0.965Mn_0.035:B films by boron plasma treatment

This paper reports that the polycrystalline Si_0.965Mn_0.035:B films have been prepared by cosputtering deposition followed by rapid thermal annealing for crystallization.The polycrystalline thin films consist of two ferromagnetic phases.The low temperature ferromagnetic phase with Curie temperature (T_c) of about 50 K is due to the Mn₄Si₇ phase in the films, while the high temperature one (T_c～ 250 K) is resulted from the incorporation of Mn into silicon. The films are treated by boron plasma excited with the approach of microwave plasma enhanced chemical vapor deposition for 40 minutes. After plasma treatment, it is observed that no extra magnetic phases or magnetic complexes exist in the films, while both the high temperature saturation magnetization and the hole concentration in the films increase. The obvious correlation between the magnetic properties and the electrical properties of the polycrystalline Si_0.965Mn_0.035:B films suggests that the hole carriers play an important role in Si:Mn diluted magnetic semiconductors.