Dependence of the indirect energy gap of silicon on hydrostatic pressure

A diamond anvil optical cell is employed to measure the pressure dependence of the fundamental indirect Γ-X transition of crystalline Si. The result is E (eV) = (1.110 ± 0.002) - (1.41 ± 0.06) × 10-3P where the pressure P is in kbar. Between 115 and 126 a transformation takes place to a phase opaque to electromagnetic radiation of wavelength between 0.3 and 2.0 μm. We believe this is the same phase transition reported by Minomura and Drickamer. A pseudopotential calculation assuming a relatively soft core is carried out and its results are in rather good agreement with experiment. © 1975.