Fabrication of ferromagnetic-semiconductor heteroepitaxial structures using ferromagnetic Ba ferrite films

为了实现高质量的铁磁半导体结构，研究了半导体表面磁性氧化层的生长条件。研究结果如下：1。采用（NH_3） _4S_x溶液对GaAs（100）衬底进行硫端化处理，在200℃的温度下通过电子束蒸发，首次在GaAs（100）衬底上外延生长出Fe_3O_4（100）铁磁薄膜。在200℃以上的衬底温度下沉积的薄膜为多晶薄膜。这与硫的解吸和砷化镓表面的氧化有关。在450℃的温度下，制备出了Fe_3O_4（100）外延薄膜，薄膜表面Fe_3O_4 [100]//GaAs[100]呈平面排列。原子力显微镜和x射线光电子能谱分析表明，外延薄膜的晶体质量和形貌主要取决于薄膜与衬底之间的晶格不匹配。在晶格常数与砷化镓相似的端氢Si（100）和Si（111）上没有Fe_3O_4薄膜和α - fe_2o_3薄膜的外延生长。这些结果表明，使用对氧稳定的离子进行表面终止是有效的，可以防止半导体表面在沉积的早期氧化。通过溅射，在α - fe_2o_3和α - al_2o_3（0001）缓冲层上外延生长出了铁磁Ba六铁体（0001）单晶薄膜。以上结果表明，以共取代Fe_3O_4代替Ba六铁氧体作为铁磁层，以GaAs作为半导体，可以实现半导体和具有强磁各向异性的铁磁氧化物的异质外延结构体系，这是本研究的目标。

In order to realize ferromagnetic-semiconductor structures with high quality, growth conditions of magnetic oxide layrs on semiconductors were investigated. The results are as follows :1.It was found for the first time that ferromagnetic Fe_3O_4 (100) thin films are epitaxially grown on GaAs (100) substrates at 200ﾟC by electron beam evaporation, when the subtrates were sulphur-terminated using an (NH_3) _4S_x solution. The thin films deposited at substrate temperatures above 200ﾟC were polycrystalline. This is associated with desorption of sulphur and resultant oxidization of the GaAs surface. The Fe_3O_4 (100) epitaxial thin films with higher quaslity were grown at 450ﾟC on the above thin films, with the in-plane alignment of Fe_3O_4 [100]//GaAs [100]. Atomic force microscopy and X-ray photoelectron spectroscopy showed that the crystalline quality and morphology of the epitaxial thin films primarily depend on the lattice mismatch between the film and the substrate. No epitaxial growth of Fe_3O_4 thin films and alpha-Fe_2O_3 thin films coccurred on hydrogen-terminated Si (100) and (111) havinb a lattice constant similar to that of GaAs. These results indicate the effectiveness of surface-termination using ions stable to oxygen, for preventing the semiconductor surface from oxidizing in the early stage of the deposition.2. It was found that the (0001) single crystalline thin films of ferromagnetic Ba hexaferrite are epitaxially grown on the buffer layrs of alpha-Fe_2O_3 and alpha-Al_2O_3 (0001) by sputtering.The above results indicate that the heteroepitaxial structure system of a semiconductor and a ferromagnetic oxide with strong magnetic anisotropy which is a goal of this research may be achieved using Co-substituted Fe_3O_4 instead of Ba hexaferrite as a ferromagnetic layr and GaAs as a semiconductor.