Dependence of the indirect energy gap of GaP on quasihydrostatic pressure and phase transition

The authors have measured the dependence of the absorption coefficient on quasi hydrostatic pressure in GaP up to 23.3 GPa in the region of the indirect gap energy (E g ) at room temperature. They have found a linear behaviour of E g with pressure up to 17 GPa with a pressure coefficient of -14.9+or-0.5 meV GPa -1 . Transmission measurements, electronic diffraction, X-ray diffraction, Raman scattering and photographs under microscope have been used to characterise the phase transition. It begins between 21 and 22 GPa. The transited phase, after depressurisation from 32 GPa, contains a mixture of polycrystalline and amorphous GaP.