AMORPHOUS CDI(2) FILMS AND THEIR CRYSTALLIZATION STUDIED BY SIMULTANEOUS MEASUREMENTS OF OPTICAL-ABSORPTION AND REFLECTION

Amorphous CdI2 films with excellent transmittance below the absorption edge were obtained by quench-deposition onto 77 K substrates. By annealing at 300-340 K, they crystallized in a previously unknown crystal structure which exhibited a very sharp exciton peak at 3.934 eV. It was suggested that the films, amorphous or crystalline, were due to covalent bonds between Cd and I atoms. The covalent bonds brought about small values of the real part of refractive index. Further annealing at higher temperatures transformed the crystal structure of the films to the ordinary, CdI2 structure. The resultant films showed anomalous spectral behavior leading to a new understanding of crystallinity in the films.