First Principle Calculation Of Electronic Structure And Structure Stability Of Tin And Tan

The transition metal nitrides represent a technologically important series of materials and owns a wide interest because it can be deposed by Chemical Vapor Deposition (CVD),Physical Vapor Deposition(PVD) and Atom Layer Depostion (ALD) and others which are also used in IC process .TiN and TaN are two kind of important transitions nitrides.The work function of TiN is about 4.5eV, near that of Silicon, which allows it to be used as a potential metal gate material. Although it has been widely studied, the analysis about the work function ,surface energy and electronic structure of different surfaces are not reported to the best of our knowledge. The present work calculated the work function ,surface energy and electronic structure of different surfaces employing density functional theory (DFT) with in the local density approximation (LDA). The study show that the preferred orientation is (111) on W substrate. And we find that the TiN film deposed on SiO2 and HfO2 should be the (111) surface terminated by Ti. Considering (111) surface is the preferred orientation, we analysed the electronic structure of (111) surface. The calculated lattice constant agrees with the experimental value. The result show that the work function of (111-Ti) surface agree well with the experimental value, while the other surfaces with a considerable different. The calculated surface energy from low to high is: 100<110<111-N<111-Ti. All the calculated surface has a metallic nature, and the (111-Ti) surface has the highest conductivity.In the second part of this thesis, Using the plane wave pseudopotential method within the generalized gradient approximation, we have studied the structural and electronic structures for several TaN phases. Our results show CoSn is the calculated ground-state structure of TaN among the five crystallographic structures that have been studied. The order of energetics stability of phase structures of TaN from low to high is: CsCl< ZnS-B3< NaCl< WC< CoSn. The higher stability of TaN in the CoSn and WC structures is due to the formation of pseudogap around the Fermi level and the stronger hybridization between N-2p states and Ta-5d states. TaN in all structures studied has metallic nature,while the NaCl structure has the highest conductivity. The calculated bulk modulus indicates that TaN in the WC structure may be a less compressibility material.