Electronic Absorption Spectrum of Thin K2ZnI4 Films

Abstract

The absorption spectrum of thin K2ZnI4 films has been investigated in the range of 3–6 eV at temperatures from 90 to 340 K. It is established that this compound belongs to direct-gap insulators; low-frequency exciton excitations are localized in the ZnI4 lattice layers and have a quasi-two-dimensional character. The spectral analysis revealed the existence of two K2ZnI4 modifications, which presumably belong to the monoclinic (I) and orthorhombic (II) phases. The temperature dependences of the spectral position and halfwidth of the low-frequency exciton band in K2ZnI4 revealed the existence of first-order phase transitions at 215 and 225 K in the monoclinic and orthorhombic phases, respectively.