Ab initiocalculations of the3C-SiC(111)/Ti polar interfaces

Abstract

Ab initio pseudopotential calculations of $3C$-SiC(111)/Ti polar interfaces have been performed and compared with ab initio calculations of $3C$-SiC(001)/Ti interfaces [Phys. Rev. B 61, 2672 (2000)] and the $3C$-SiC(111)/TiC interface [Phys. Rev. B 55, 16 472 (1997)] and with experiments on $6H$-SiC(0001)/Ti interfaces. Two types of interfaces, Si- and C-terminated interfaces, are dealt with in order to examine the dependence on the atom species at the interface. As to stable atomic configurations, the six candidates for each interface are examined. In the most stable configurations, the interfacial Ti atoms are located on top of the center of the triangle of surface atoms of SiC ${(T}_{4}$ site for the Si-terminated interface and ${H}_{3}$ site for the C-terminated interface) rather than on top of surface atoms of SiC ${(T}_{1}$ site). There are serious differences in the bond lengths, bonding nature, and adhesive energies between the Si- and C-terminated (111) interfaces and between the SiC(111)/Ti and SiC(111)/TiC interfaces, respectively. The C-terminated interface has strong interfacial bonds with a large adhesive energy rather than the Si-terminated one, similarly to the (001) interfaces. However, there exist substantial differences between the (111) and (001) interfaces, which can be explained by the interface morphology such as the number of back bonds and the neighboring atoms of interfacial atoms, and the number and direction of surface dangling bonds. A calculated p-type Schottky barrier height (SBH) of the C-terminated interface is smaller than that of the Si-terminated one. This SBH relationship is in good agreement with the experimental results of the $6H$-SiC(0001)/Ti interfaces and consistent with previous ab initio results of the $3C$-SiC(001)/Ti interfaces. The dependence of SBH on the interface atom species can be explained by the following two factors: the relationship of intrinsic band structures between two materials and the interface dipole caused by the interfacial charge distribution. On the other hand, the extended Schottky model has been examined using the theoretical work functions including effects of the surface structure for the SiC(111)/Ti and SiC(001)/Ti interfaces. The obtained relationship of the SBH between the Si- and C-terminated interfaces is contrary to the ab initio results and experiments. It is clear that the SBH at the interface is dominated by the interfacial atomic and electronic structures, and is unable to be estimated by the surface properties simply.