Effect of hydrostatic pressure on the second order Raman spectrum of GaP

Measurements of the effect of hydrostatic pressure on the major features in the second order Raman spectrum of GaP are reported. The entire second order spectrum is decomposed into its irreducible symmetry components. The mode Grüneisen parameter for the TA (X> → K) phonons is negative and the parameters for TO(L) and LO(Σ) are somewhat larger than those at the center of the zone. Finally, we observe that the shift under pressure of the 2LO(Γ) structure is slightly less than twice the first order LO(Γ) shift.