Quantum Well Effects in Ionic Insulators and Metals.

自从1986年在交替的KCI-KBr多层结构的吸收光谱上发现KbR激子带的量子尺寸效应以来，我们主要研究了几种碱卤化物中的量子阱激子，积累了大量的知识。这些认识简要地解释如下：在KCI-KBR或RbCL-XBR多层结构的吸收光谱中，出现在最低能量处的激子带(KBR)在两种效应下表现出蓝移，即由于量子限制导致激子动力学的增加和由于界面混合物的形成而使势垒中的带隙增加。而在宽度为激子玻尔半径的十倍宽的势垒中，激子波函数仍然受到有效的限制，似乎使激子带的上升更加陡峭。对于未退火的多层膜，层-层界面混合物对蓝移的影响可以通过对多层膜进行适当的温度逐层热退火来减小，实现了无界面失配和界面混合物的结构。界面混合物的形成强烈依赖于退火温度和蒸发速度，目前认为温度为180ﾟ-200ﾟC，蒸发速度小于1a^ﾟ/s为宜。还发现，如果晶格常数与衬底晶体的晶格常数相差很大，界面失配效应在薄膜小于100A·ﾟ的情况下是很重要的。

After discovery of the quantum size effect in the KBr exciton band on the absorption spectra of alternate KCI-KBr multilayer structure in 1986, we have mainly investigated the quantum well excitons in several alkali halides and accumulated lots of knowledges on them. These knowledges are briefly explained as the follows.The exciton band due to the well (KBr) which appears at the lowest energy on the absorption spectra of KCI-KBr or RbCl-xBr multilayer structures exhibits a blueshift in affecting with two effects, namely an increase of the exciton kinetic due to quantum confinement and an increase of band gap in the well due to interface mixture formation. Whereas the confinement of exciton wave function is effectively occurred even in the well with width wider by ten times of exciton Bohr radius and seems to make the rise of exciton band steeper appreciably.The influence of the layer-layer interface mixture to the blueshift which is remarkable in the noannealed multilayer can be decreased by thermal annealing at appropriate temperature for layer by layer, and an interface mismatch free and interface mixture free structure is realized in annealed RbCl-KBr multilayer. The.interface mixture formation strongly depends on annealing temperature and evaporation, speed, and at the present, it is considered that the temperature 180ﾟ-200ﾟ C and the speed less than 1A^^ﾟ/sec are favorable.It is also revealed that, if.there is a large difference of lattice constant between the layer and the substrate crystal, the interface mismatch effect is important in the case of very thin film less than 100A^^ﾟ.The experimental chamber which is just constructed by the grant will be worked to research the conditions of the thermal annealing and the evaporation speed of thin layers in near future.