Effect of interfacial reactions on electrical properties of Ni contacts on lightly doped n-type 4H-SiC

Electrical properties of Ni contacts on lightly doped n-type 4H-SiC (4.2x10(15) cm(-3)) were interpreted in terms of changes in microstructure and atomic composition at the Ni/SiC interface. The effective Schottky barrier height was increased from 1.55 to 1.81 eV after annealing at 600degreesC, but decreased to 1.25 eV at 800degreesC. When the Ni contact was annealed at 900degreesC, ohmic contact was formed. Two kinds of Ni silicides, Ni(31)Si(12) and Ni(2)Si, were observed in the annealed contact and the work function of silicide increased by 0.36 eV. The atomic composition of Si in nickel silicides forming at the interface increased with the elevation of annealing temperature. This implies that silicidation process proceeded through the outdiffusion of Si, leaving Si vacancies below the contact via increase in Schottky barrier height. The temperature (900degreesC) for ohmic contact formation was higher than the silicidation temperature (600degreesC) in forming Ni(31)Si(12) and Ni(2)Si phases. An abundance of C atoms were outdiffused to the surface of contact layer, leaving C vacancies below the contact. C vacancies act as donors for electrons, which caused the increase in net electron concentration, leading to the formation of the ohmic contact on n-type SiC through the reduction of depletion layer width. (C) 2002 The Electrochemical Society.