Anomalous pressure behavior of ZnSe Raman spectrum

The effects of pressure on the 1- and 2-phonon Raman spectrum of ⁶⁸Zn⁷⁶Se are investigated at 295, 125, and 11K. At 295K, the TO(γ) line-width exhibits an anomalous 10-fold broadening in the pressure range 10.5-13GPa, prior to the B1 phase transition. Other spectral features remain reasonably sharp. At 125 and 11K the TO(γ) anomaly is not seen. After the phase transition, a broadband is also seen in the TO(γ) region for a wide range of downstroke pressures. Two explanations are considered: strong anharmonic coupling between TO(γ) and (TO2-TA1)(X,K) difference modes, and structure or local bonding changes within the ZnSe lattice. First principles calculations of the 1- and 2-phonon density of states as a function of pressure are carried out and used to test the effect of the TO(γ)→(TO 2-TA 1)(X,K) decay process. The results cannot rule out contributions from additional anharmonic channels and/or structural disorder effects.