Optical Properties of Thin Alkali-Halide Crystals Prepared by Reacted Epitaxial Method.

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The recent development of the molecular beam epitaxy (MBE) technique makes it possible to produce sophisticated heterostructures. In the course of this development epitaxial condition for semiconductor materials have been well clarified and plenty of know-how has been accumulated. Compared with this, the epitaxial growth of insulators has been rather little studied so far. In the present study, we have studied the heteroepitaxial growth of KI on alkali halide substrate by using reacted epitaxial method. Optical properties of thin KI films obtained have been investigated in situ during the growth of KI films.At first stage, HI gas was evaporated on a KCl (001) substrate crystal at low temperature (-10K). Next, the temperature of the substrate was increased slowly. Transmission spectra near the absorption edge of KI were monitored in situ with increasing temperature. As a result KI film crystal was found to grow at temperatures of 180-220K in-10A to-100A thickness. It is also found that the film thickness can be controlled depending on the amount of HI gas evaporation.In order to characterize the quality of the films, we have examined the exciton absorption spectra and the luminescence spectra at 10K systematically without exposure to the atmosphere. By comparison with the previous results from the MBE method, the peak energy and the linewidth of the first exciton band of KI films were the almost the same ones as the MBE Films, and were continuously changed to those of a bulk crystal. These facts suggest that the thin films obtained in the present study posses a good quality as that from the MBE method and the lattice relaxation is limited very near to the interface of the substrate. Heteroepitaxial growth of other systems by this reacted epitaxial method are in progress and will be reported in the near future.