Electronic structures and optical properties of Mn-doped LiCaN new diluted magnetic semiconductors

Using the first-principle density functional theory based on the full potential linearized augmented plane wave method, the geometric structures of new diluted magnetic semiconductor Li-1 +/- y(Ca1-xMnx)N (x=0, 0.125; y=0, 0.125) were optimized. The electronic structures and optical properties were calculated and discussed in detail. The results show that the magnetic and electrical properties of the doped system can be separately regulated by Mn doping and Li off-stoichiometry. When Mn doped in the system, the electrons of the Mn 3d split into triply degenerate t(2g) and double degenerate e(g) energy levels. Meanwhile, the Mn 3d states hybridize with Ca 4s and N 2p states, leads to the systems display half-metallic ferromagnetism. In Li excess and insufficient compounds, the band gaps and magnetic moments decrease, while the Curie temperature and electrical conductivity increase, and they exhibit 100% spin injection. In addition, the half-metallicity of Li insufficient system enhances significantly. In Li excess compound, Jahn-Teller effect leads to the highest Curie temperature and the lowest formation energy. Comparing optical properties indicates that the imaginary part of dielectric function, complex refractive index function, optical absorption function and the imaginary part of photoconductivity are all affected by Li stoichiometry. The energy loss functions of the doped systems show obvious blue-shift effect and much stronger plasma resonant frequency, and the oscillating range of plasma is wider in Li excess and insufficient compounds.