Phonon Raman spectra of layer compound GaSe

Raman scattering spectra of GaSe were examined at various temperatures (80 to 400 K) and the far‐infrared transmittance was obtained in the energy range from 10 to 30 cm−1. It is shown that the band at 20 cm−1 is both Raman‐ and infrared‐active. Results of the resonant Raman enhancement in GaSe indicates that the Raman band at 250 cm−1 is due to a LO mode. Comparison between the Raman spectrum of GaSe and that of Gas confirms this. These facts can be explained by considering the hexagonal GaSe as the ϵ‐type which lacks inversion centre. Six Raman bands observed in GaSe are assigned to normal modes on the basis of the ϵ‐type. An E′ (TO) mode is degenerated accidentally with an E″ mode at 211 cm−1.