The vibrational, electronic, and crystalline properties of n -type chlorine-doped ZnSe (ZnSe:Cl) layers with a carrier concentration from 8.2× 1015 to 1.8× 1018 cm-3 are studied by Raman spectroscopy. The spectral line shapes of the longitudinal-optical-phonon and plasmon coupling mode are analyzed using the Raman scattering efficiency and the dielectric function to obtain the electron densities and mobility. The splitting of the transverse-optical (TO) phonon and the redshift of the chlorine-related impurity vibration mode are clearly observed when pressure is applied. The semiconductor-to-metal phase transition pressure of ZnSe:Cl layers declines as the carrier concentration increases, indicating that n -type doping reduces crystal stability. Additionally, the pressure-induced weakening of the longitudinal-optical-phonon-plasmon coupling efficiency suggests that pressure tends to degrade the n -type characteristic of ZnSe:Cl because of the emergence of the new deep donorlike state.