First-principles Study Of Magnetic Properties And Work Function Of Ni-based Materials

With the rapid development of technology, the continuous downscaling of semiconductor devices is now near its limit, it is necessary to seek alternative high-k gate dielectrics constant materials to substitute the traditional SiO2gate dielectric for the SiO2does not satisfy the need of high integration of MOSFET devices. The polycrystalline Si (poly-Si) gate must be replaced by metal gates because the poly-Si gate encounters many problems when integrated with high-k dielectric, for example gate depletion effect, Fermi level pinning, and high gate resistance. So there is immense interest in theory and experiment research. In this dissertation, first-principles methods based on density-functional theory were used to calculations the work function and magnetism of NixCu1-x alloy materials, NiCr alloy materials, and Carbon Adsorbed on Ni (111). The main contents are as follows:First of all, the research background were introduced, including the scaling issues of traditional SiO2gate dielectric, the inevitability and difficulty of substitute for poly-Si gate by metal gate, the feasibility of spin modulation surface work function. In addition, the details to the theoretical basis and implementation process of first-principles calculation involved in this thsis were also presented.Secondly, the magnetism and work function of NixCu1-x alloys were investigated using first-principles methods. Results of our calculations reveal that surface orientation has important effect on the magnetization and work function of NixCu1-x. For a given surface orientation, the inner distribution of Cu atoms does hardly effect on the magnetization and work function. We also compared the results of spin polarization to the non-polarization results’, our work suggests surface atomic modification could be a promising way to tuning work function of alloy metal gate.Next, surface work function and affection of spin modulation on work function of NiCr alloys were studied. We especially focus on the effects of difference spin configuration on the work function by collinear and non collinear calculation methods. Our results indicated that work function of metal NiCr alloy is strongly affected by surface orientation and spin polarization. Using the non-collinear method to constrain the size and spin direction of atoms’magnetic moment, there is difference work function between different surface spin configurations.Finally, work function and magnetism of Ni (111) with different coverage carbon atom adsorbed on it were investigated using first principles methods. Calculated results show that the adsorption energy decreases with increasing carbon coverage. The adsorbed carbon atom induces the change of the work function and magnetism of Ni (111). The work function increases with increasing coverage degree6, and the carbon adsorption has the magnetic moments of Ni atoms at the surface and sub-surface layers decrease obviously.