A Study of the Schottky-Barrier Height of Nickel Germanosilicide Contacts Formed on $\hbox {Si}_{1-x}\hbox {Ge}_{x}$ Epilayer on Si Substrates

Formation and electrical properties of nickel silicidized n-type Si and $\hbox {Si}_{1-x}\hbox {Ge}_{x}$ epilayers on a Si substrate are comparatively studied. The improvement of thermal stability of germanosilicide can be attributed to the thicker NiSi(Ge) film and the delay of phase transformation with Ge incorporation, as well as the reduction in interface energy with Ge segregation at the interface. The Schottky-barrier heights (SBHs) of the contacts formed by sputtering Ni on the strained $\hbox {Si}_{1-x}\hbox {Ge}_{x}$ ( $x = \hbox {0.07}$ and 0.2) epilayers significantly increase after germanosilicidation and with increasing annealing temperature, markedly contrasting to the quick drop of SBH of the silicidized Si contact made by the same process. The raise of SBH of the $\hbox {Ni/Si}_{1-x}\hbox {Ge}_{x}$ contact after germanosilicidation and with increasing annealing temperature is dominated by a Fermi-level pinning effect due to Ge segregation at the interface and the generation of dislocations driven by strain relaxation in the $\hbox {Si}_{1-x}\hbox {Ge}_{x}$ epilayers, rather than the reduction in work function when Ni transforms to NiSiGe during the germanosilicidation process.