Electrical properties of semimetallic silicon III and semiconductive silicon IV at ambient pressure

Microcrystalline samples of BC8 silicon III and hexagonal silicon IV, grown under high pressure in the diamond anvil cell, remain metastable at ambient pressure. Hall-effect and low-temperature resistivity measurements show Si III to be a hole semimetal with p≊5×${10}^{20}$ ${\mathrm{cm}}^{\mathrm{-}3}$. Photoconductivity data show that Si IV, like Si I, is an intermediate-gap semiconductor. The observed behavior confirms theoretical predictions on these two new elemental materials.