Epitaxial Ge-Si alloy films were grown on Si(100) by molecular beam epitaxy, subsequently given a shallow P implant, and subjected to rapid thermal processing. Heat treatment causes solid-phase epitaxial regrowth of the amorphized implanted layer similar to the case of pure Ge. Phosphorus redistribution, loss, and trapping at the Ge-Si/Si interface are also observed. Anomalous electrical activation is observed for P concentrations below 1 at.%, where the-carriers are either trapped or compensated at room temperature, but not below 100K. Analyses were carried out by Rutherford backscattering and channeling, secondary ion mass spectrometry, and temperature-dependent electrical transport.