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

分子束外延（MBE）技术的发展使得制备复杂的异质结构成为可能。在这一发展过程中，半导体材料的外延条件得到了很好的澄清，积累了大量的技术诀窍。与此相比，绝缘体的外延生长迄今为止研究得相当少。本论文采用反应外延法研究了KI在碱金属卤化物衬底上的异质外延生长。在生长KI薄膜的过程中，首先在KCl（001）衬底晶体上低温（-10K）蒸发HI气体，原位生长KI薄膜。接着，缓慢地升高基板的温度。随着温度的升高，在原位监测KI的吸收边附近的透射光谱。结果发现，在180- 220 K温度范围内生长出厚度为-10A至-100A的KI薄膜晶体。为了表征薄膜的质量，我们在10 K下系统地测量了激子吸收谱和发光谱。与MBE方法的结果相比，KI薄膜的第一激子带的峰值能量和线宽与MBE薄膜的几乎相同，并不断地向体晶体的变化。这些事实表明，在本研究中获得的薄膜具有良好的质量，从分子束外延方法和晶格弛豫是有限的非常接近衬底的界面。其他系统的异质外延生长，这种反应外延方法正在进行中，并将在不久的将来报告。

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.