Preparation and properties of ferroelectric/semiconductor hybrid-lattice inrefaces

本研究的目的是使氧化物（铁电体）/半导体混合晶格界面，并澄清具有上述界面的异质结构的电学和/或光学性质。主要研究结果如下：1）利用分子束外延（MBE）技术在氢原子封端的Si（111）表面外延生长了氧化锶薄膜。氢终止工艺是获得氧化物/Si混合晶格界面的关键。2）为实现原子层外延，研制了分子束外延全自动控制系统。利用该系统制备了钛酸锶（STO）和钛酸钡（BTO）的人工超晶格和人工调制结构。获得了具有完美晶格匹配（混合晶格界面）的清洁界面。调制结构的铁电特性与STO和BTO的简单固溶体不同。3）在蓝宝石衬底上制备了钽酸锂/半导体氧化锌铁电异质结构，并利用椭圆偏振光谱仪测量了其光学特性。针对透明薄膜椭偏测量中存在的各种问题，开发了椭偏测量操作与分析软件。该系统测定的光学常数与散装样品的报道数据一致。

The object of the present study is to make oxide (ferroelectrics) / semiconductor hybrid-lattice interfaces and to clarify the electric and/or optic properties of heterostructures having the above interfaces. The results obtained were summarized as follows.1) Strontium oxide thin films were epitaxially grown on a hydrogen-terminated Si (111) surface by a molecular beam exitaxy (MBE) process. The hydrogen termination process was essentially important to obtain an oxide/Si hybrid-lattice interface.2) A full automatic deposition control system was developed for MBE process to realize an atomic-layr epitaxy with the resolution below mono-layr. Artificial superlattices and artificially modulated structures of strontium titanate (STO) and barium titanate (BTO) were prepared by this system. Clean interfaces with a perfect lattice matching (hybrid-lattice interface) were obtained. The ferroelectric properties of the modulated structures were found to be different from that of a simple solid solution of STO and BTO.3) A ferroelectric lithium tantalate/semi-conductive zinc oxide heterostructure was prepared on a sapphire substrate and its optical property was measured by a spectroscopic ellipsometer. Software for operation and analysis of ellipsometry was newly developed to solve various problems existing in the ellipsometry of transparent films. The optical constants determined by this system was well consistent with the reported data for bulk specimens.