Time-resolved electrical conductivity measurements on monocrystalline doped Si were performed under shock compression up to 23GPa followed by release. With increasing normal stress, the electrical conductivity of Si increased monotonically by 5 orders of magnitude and reaches that of 'poor' metals. The stress dependence of the conductivity comprises two parts: a steep rise and a 'plateau'. The 'plateau' conductivity corresponds to the metallic state of Si; it does not depend on the compression regime or the doping type or amount of impurity. The onset of the metallic phase corresponds to a shock stress of about 10GPa; most of the specimen was metallic at 12GPa. The state of shock-compressed Si proves to be extremely defective. The defect concentration in shocked Si exceeds the equilibrium concentration by five orders of magnitude and exceeds the defect concentration in classic metals by an order of magnitude. This indicated distinctive features of brittle solid deformation. Experimentally, the metallic phase proves to be metastable. Releasing stress caused a temporary delay of the reverse transition.

Metallization of Silicon in a Shock Wave - the Metallization Threshold and Ultrahigh Defect Densities. S.D.Gilev, A.M.Trubachev: Journal of Physics - Condensed Matter, 2004, 16[46], 8139-53