Several 265-nm-thick metastable pseudomorphic Ge0.12Si 0.88 films grown on a Si(100) substrate by molecular-beam epitaxy were implanted at room temperature with 100 keV phosphorus ions to a dose of 1.5×1015/cm2. The implantation amorphizes the top portion (∼190 nm) of the GeSi layer and leaves the rest of the film single crystalline. Implanted and nonimplanted samples were subsequently annealed simultaneously in vacuum for 30 min from 400 to 800 °C. The implanted samples undergo layer-by-layer solid-phase-epitaxial regrowth during annealing at or above 500 °C. The regrown GeSi layer is relaxed with a high density of threading dislocations (∼1010-1011/cm2). The nonamorphized portion of the layer remains fully strained when annealed between 400 and 600 °C. At or above 700 °C misfit dislocations are observed at the Si/Ge0.12Si0.88 interface. After 800 °C annealing the strain in the whole epilayer is fully relaxed. The strain relaxation is facilitated by the implantation. The presence of phosphorus in GeSi raises its regrowth velocity by about an order of magnitude over that of Ge0.12Si0.88 amorphized by irradiation of Si. The implanted phosphorus reaches ∼100% activation after the completion of solid-phase-epitaxial regrowth. The room-temperature sheet electron mobility in GeSi is ∼20% below that of a Si sample implanted and annealed under the same conditions. It is concluded that metastable Ge0.12Si0.88 on Si(100) amorphized at room temperature by P implantation and recrystallized by solid-phase epitaxy can- not recover its crystalline perfection and its pseudomorphic strain upon steady-state furnace annealing.