부산대학교 도서관

Slab samples of ∈-GaSe have been prepared with the optical axis (the c axis) in the plane of the face. Previously, most optical studies were made on slabs cleaved from crystals, which have the c axis perpendicular to the face. The infrared absorption spectra of ∈-GaSe were measured at room temperature in the spectral range of 4000-450 cm[sup -1] for the e-ray (polarized parallel to the optical axis) and the o-ray (polarized perpendicular to the optical axis). The maximum value of the optical absorption coefficient, α, for both geometries, does not exceed 2.5 cm[sup -1] (Ec). We find anisotropy in the transmission in the spectral range below ∼2250 cm[sup -1], due to the free carrier absorption, only in the e ray. At T=300 K, acoustic lattice vibrations are the dominant scattering mechanism for carriers moving parallel to the c axis. Absorption bands were observed in e-ray spectra at 891, 945, 1093, and 1270 cm[sup -1]. These bands may be due to multiphonon absorption, or to localized vibrational modes stemming from unintentional impurities. It is suggested that the sharp absorption at 891 cm[sup -1] may be due to hole transitions from the lowest-lying valence band in the center of the Brillouin zone to the top of the valence band (Γ[sup +, sub 6] → Γ[sup -, sub 4] transition). [ABSTRACT FROM AUTHOR]