High-pressure Raman spectra of wurtzite aluminum nitride were measured up to 25 GPa. The Raman-active modes in wurtzite-AlN were obtained up to the wurtzite-to-rocksalt transition at 20 GPa and their pressure coefficients compared with those obtained from ab initio lattice dynamics calculations. A slight decrease of the LO–TO splitting under pressure has been measured. We also report Raman scattering of the rocksalt phase of AlN during downstroke. The comparison of previously reported Raman scattering in rocksalt-GaN and ab initio calculations suggests that the Raman scattering we have measured in rocksalt-AlN likely corresponds to the one-phonon density of states of the rocksalt phase. A partial return to the wurtzite phase is found at ambient pressure after fully releasing pressure.
