Phase Diagrams of Silicon and Germanium to 200 kbar, 1000°C

The phase diagrams of Si and Ge have been investigated experimentally over a P, T range of about 200 kbar and 1000°C by observing electrical resistance behavior. For Si the boundary between the diamond cubic form and the metallic form extends from about 120 kbar at room temperature to about 150 kbar, 810°C, where melting occurs at the triple point. For Ge the corresponding boundary extends from about 115 kbar at room temperature to about 103 kbar, 600°C. A line drawn through the triple points for Sn, Ge, and Si, and extended, suggests that the diamond—metal—liquid triple point for carbon may be around 500 kbar, 2400°C. When the metallic forms are decompressed at room temperature they transform back to semiconducting forms different and more dense than the original diamond cubic forms. Upon heating these denser forms to a few hundred degrees at room pressure they transform to the usual diamond cubic forms. The absolute resistivity and temperature coefficient of resistance of metallic Ge has been determined.