Pressure dependence of the direct absorption edge of InP

The variation of the lowest direct absorption edge of InP with pressure has been measured at room temperature with a diamond anvil cell for pressures up to the phase transition (100 kbar). Both transmission and luminescence techniques were used. The gap varies sublinearly with pressure but linearly with lattice constant: the gap deformation potential so obtained is a=-6.35±0.05 eV. This result is discussed in the light of theoretical calculations. The observed luminescence intensity remains nearly constant as a function of pressure up to 90 kbar. At this pressure the efficiency begins to decrease thus signaling the crossing of the Γ and X conduction-band minima which we estimate to occur at 104 ±{} 1 kbar. The pressure coefficient of the Γ-X indirect gap is found to be -(3 ±{} 1) ×{} 10^-6 eV/bar.