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Recent experiments have demonstrated a reduction of Fermi-level pinning in contacts to n-type Ge by the insertion of a thin tunnel barrier at the interface. The presence of fixed charge in these interface layers can contribute to Schottky-barrier reduction. This work theoretically studies the effect of tunnel-barrier fixed charge on the specific contact resistivity. By simulating various tunnel-barrier materials and fixed-charge densities, we estimate the magnitude of fixed charge required for this mechanism to play an important role in Fermi-level unpinning.