The thermal stability of a nickel germanide film formed on a tensile-strained Ge epilayer on a silicon substrate with a low-temperature $hbox{Si}_{0.77}hbox{Ge}_{0.23}$ (50-nm)/Ge (50-nm) buffer is investigated. A record temperature of 700 $^{circ}hbox{C}$ for the stability of sheet resistance of nickel germanide is reported, which is increased by about 150 $^{circ}hbox{C}$ compared to that on bulk Ge and comparable to the temperature for nickel silicide on the Si substrate. The improvement of the thermal stability is demonstrated due to the delay of the agglomeration of the nickel germanide film on Ge-on-Si, which is proposed to be attributed to the increase of the tensile strain in the Ge epilayer during thermal annealing due to the thermal mismatch between Si and Ge.
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