Impact of ion implantation on nickel germanides formation with pure-Ge substrate and the electrical dependence of NiGe/Ge schottky diode on contact size

The material and electrical characterization of nickel germanides on pure n-(100) Ge are investigated in this paper. The nickel germanides were achieved by rapid thermal annealing (RTA) in N2 ambient for 60s at different temperature. And X-ray diffraction (XRD) and Raman measurements were used to determine the crystal phase of Ni germanides. The results show that the ion implantation of BF2 before germanidation is favorable for the formation of low-resistivity monogermanide phase (NiGe). Ni-rich germanide phase exists when annealed at 300??C for pure-Ge without BF2 implantation, while only NiGe is formed for that with BF2 implantation. As a result, the sheet resistance of the film annealed at 300??C is ??9.6??/ and ??3.8??/ for the samples without/with BF2 implantation, respectively. Besides, we firstly observed the Raman peak at ??217cm-1 corresponding to NiGe, which has not been reported till now. In addition, it is also experimentally demonstrated that the Ti-capping layer technique is beneficial to better surface morphology. Furthermore, the electrical characteristics of NiGe/pure-Ge Schottky diodes is presented. The strong dependence of Schottky barrier height (??b) and the ideality factor (n) on the contact hole size is also firstly observed through the experiments. When annealed at 400??C, the Schottky barrier height (??b) of Schottky diodes formed on pure-Ge substrate decreases from 0.53eV to 0.42eV with the contact size decreasing, while the ideality factor(n) increases remarkably, which may provide the guideline for the application to Schottky source/drain germanium transistors.EI