Microstructure and Physical Property of a-Si : H/a-SiC : H Super-Lattices

近年来，由不同材料的薄层交替构成的人工超晶格作为一类新材料受到越来越多的关注。在金属/金属或半导体/半导体等不同的层状体系中进行了大量的研究，并报道了新的现象和应用潜力。本文研究了用磁控溅射装置制备的A - si / A - sic和A - si: H/ A - sic: H层状薄膜的微观结构和物理性质。得到的结果如下：1。(1)透射电镜显示，厚度小于几nm的a- si /a- sic薄膜和氢化薄膜连续，无沟道和孔洞。因此，在目前的制备条件下，即使在沉积的早期阶段，也可以形成连续的薄膜。(2)对不同上部结构周期的样品进行了x射线小角散射实验。观察到高次衍射峰的第一个清晰的外观。暗示上层建筑的形成。从观测峰位得到的周期与制备时设计的周期一致。(1)利用真空紫外光电子能谱和光吸收测量得到了a-Si/a-SiC和a-Si: H/a-SiC: H超晶格的能带图。结果表明：a-Si/a-SiC的价带和a-Si: H/a-SiC: H的导带均存在明显的能带偏移。(2)a-Si/a-SiC层膜的光隙与a-Si层厚度无关，而a-Si: H/a-SiC: H层膜的光隙随着a-Si: H层厚度的减小而增大，说明存在量子尺寸效应。

In recent years there has been a growing interest in artificial superlattices consisting of alternating thin layers of different materials as a new class of materials. A number of studies have been carried out on various layered systems such as metal/metal or semiconductor/semiconductor, and new phenomena and potentials for applications have been reported The present study deals with microstructures and physical properties of a-Si/a-SiC and a-Si : H/a-SiC : H layered films prepared using r. f. magnetron sputtering apparatus with two kinds of targets. The results obtained are as follows.1. Microstructures(1) Transmission electron microscopy showed that a-Si/a-SiC films and hydrogenated ones having a thickness of less than a few nm were continuous without channels and holes. Hence it is considered that a continuous films might be formed even at the early stage of deposition under the present preparation conditions.(2) The X-ray small-angle scattering experiments were carried out on the samples with various superstructure periods. The clear appearance of the first diffraction peak to higher harmonics, was observed. Suggesting the formation of superstructure. The period obtained from the observed peak positions was in agreement with that designed on preparation.2. Physical properties(1) Energy-band diagrams for a-Si/a-SiC and a-Si : H/a-SiC : H superlattices were obtained using vacuum ultraviolet photoelectron spectroscopy and also from optical absorption measurements. The results showed that the pronounced band offsets appeared at the valence band for a-Si/a-SiC and at the conduction band for a-Si : H/a-SiC : H.(2) Optical gaps of a-Si/a-SiC layered films were independent of thickness of a-Si layers, and on the other side, those of a-Si : H/a-SiC : H films increased with decreasing of the a-Si : H layer thickness, meaning quantum size effect.