Preparation and fundamental optical absorption edge of In-4(P2Se6)(3) single crystals

Methods of synthesis and growth of good quality, uniaxial In-4(P2Se6)(3) si ngle crystals were developed. The temperature dependence of the optical abs orption edge of these crystals was studied at high absorption levels in the spectral range of direct optical transitions. At low temperatures, we obse rved an exciton band corresponding to the optical absorption with the forma tion of direct s-excitons. In the long-wavelength spectral range of the abs orption edge, Urbach tails were observed. We showed that the exponential de pendence of absorption coefficient on photon energy is a consequence of exc iton-phonon interaction, whose mechanism is explained within the framework of Dow-Redfield theory. The influence of disorder on the width of Urbach ta ils was analyzed as well. (C) 2000 Elsevier Science Ltd.