Photoluminiscence and absorption of emission by phonons of indirect transitions in layered GaS single crystals

Absorption in E||b and E⊥c polarizations and photoluminescence at the absorption edge were studied at temperatures range 10–300 K. It was found that the smallest indirect transitions take place from the minimum of conduction band C₁ (point M) to the maximum of valence band V₁ in the Brillouin zone center (point Γ or nearby). A distance between these extrema is 2.4484 eV at 10 K. In addition, the magnitude of indirect transitions from the second band C₂ (point M) to valence band V₁ (Brillouin zone center) is 2.4912 eV at 10 K. The splitting of C₁–C₂ bands in M point of the Brillouin zone is equal to ∼43 meV. The indirect transitions from third conduction band C₃ (point K) to valence band V₁ in the nearby of Γ point are equal to 2.7683 eV at 10 K. The splitting of conduction bands C₂ (point M) and C₃ (point K) is higher than one for the splitting C₁–C₂. It was observed bands associated with self-absorption of photoluminescence emission by phonons with symmetries E_1g¹+A_1g², A_1g²+A_1g¹ and A_1g²+E_2g² involved in indirect transitions.