Optical absorption, resistivity, and phase transformation in CdS at high pressure

Optical-absorption measurements to 100-kbar hydrostatic pressure have been performed on CdS in a diamond anvil cell. The results indicate that the energy gap is direct in the wurzite phase and indirect in the rock-salt phase, which becomes stable above ∼ 28 kbar. The initial dEg/dP≈0, followed by red shift above 60 kbar in the rock-salt phase, is interpreted in terms of a changeover from Σv→Xc to Lv→Xc gap. The measured gap of 1.7 eV and the above assignments would be consistent with the band-structure calculations for the rock-salt phase of CdS