A semiquantitative subplantation model for hyperthermal particle enhancement of epitaxy is proposed and applied to the system of Si+ ion beam homoepitaxial growth : The mechanism proposes that storage of a portion of the kinetic energy of the hyperthermal particles as interstitial atoms and subsequent release of this energy is a general phenomenon that is responsible for ion beam enhanced epitaxy and growth of metastable materials. A generalized epitaxial phase diagram which illustrates the energy-temperature synergism is constructed. This provides an understanding of the limited and unlimited silicon homoepitaxial growth from thermal (molecular beam epitaxy) and hyperthermal Si atoms, respectively. Four regions of energy-temperature space have been identified in reference to epitaxial growth : I. Unlimited epitaxy due to high thermal energy; II. Interstitial registry-limited epitaxial growth; III. Hyperthermal particle enhanced epitaxy; IV. Defect-limited epitaxial growth.