Lattice dynamics of ZnSe x S1 − x semiconductor crystals

Recently ultrabroadband infrared solid state lasers based on a new vibronic material Cr2+:ZnSe x S1–x were demonstrated [1–3]. Cr2+ ion substitutes the metal ion (tetrahedral sites), the crystal field of the solid solution is responsible for large inhomogeneous broadening of Cr2+ electron states. The crystal field can be reconstructed by investigation of lattice dynamics — optical phonon parameters and dielectric function in IR. We paid special attention to investigation of vibrational and infrared spectroscopic properties of ZnSe x S1 − x crystals. A very interesting and somewhat unexpected result of these studies was the existence in the crystals of effective S-Se dipoles, which generate an additional deep dynamically charged level in the forbidden gap of the semiconductors. The results of the first-principles calculations of both the phonon structure and the electron localization in ZnSe x S1–x crystals as well as acceptor levels in Cr2+: ZnSe crystal are discussed.