Amorphous alloys have been produced by Ar+beam irradiation of Au‐Ge thin‐film bilayers. Two different average compositions have been detected for implantation at 80 or at 300 K, respectively. Each amorphous phase decomposes into a crystalline one after aging at room temperature for several hours. The composition and structure of such crystalline phases are also controlled by the irradiation temperature. Prolonged annealing at 45 °C produces precipitation of pure Au and Ge respectively. The metastable crystalline phase formed at LN2T irradiation is tetragonal and has a composition range close to the &khgr; phase formed after splat cooling technique. The room temperature phase has instead an hexagonal structure.