Study on magneto-transport properties of semiconductor/magnetic-material heterostructures by ballistic electron emission microscopy

本研究的目的是利用弹道电子发射显微镜和光谱学（BEEM/BEES）来探索半导体/磁性材料纳米结构中自旋相关的电子隧穿。得到的主要结果如下：1。我们开发了低温BEEM/BEES测量系统，可以在超高真空下完成从样品制备到LT-MEEM/BEES测量的整个测量过程。关于新型表面半导体/磁性材料纳米结构的制备(1)我们研究了不同表面重构在GaAs（001）表面上的铁沉积，发现4x6重构表面具有最可靠的Shottky接触。(2)为了明确MnAs和CrAs在锌闪锌矿结构中结晶的性质，基于STM观测和LEED IV分析，提出了亚单层MnAs覆盖GaAs（001）的表面结构模型。根据第一性原理计算，该结构有望具有半金属带结构。(3)为了制备硅化铁相关的半导体/磁性材料表面纳米结构，研究了在硅表面沉积铁。结果表明，ag端部Si(111)√<3>x√<3>-Ag表面可以制备直径为10 ~ 20 nm的Fe_3Si纳米点。3 .对不同厚度的GaAs(001)/Fe肖特基接触的bee观测表明，根据电子能量的不同，电子在Fe层中的衰减长度在1.52 ~ 2.74 nm之间，比以往的报道要长。通过对GaAs(001)c（4x4）表面的RHEED摇摆曲线和LEED IV分析，可以发现GaAs(00l)c（4x4）表面不是单一结构，至少有两种相似但不同的结构。此外，它们之间的相变甚至可以在衬底温度低至300℃时发生，并且基于c（4x4）表面的多结构性质，似乎可以很好地解释GaAs(001)c（4x4）表面上低温MBE生长的混乱行为。少

The aim of this study is to explore the spin-dependent electron tunneling in semiconductor/magnetic-material nano-structures by using ballistic electron emission microscopy and spectroscopy (BEEM/BEES). The major results obtained are as follows.1.We have developed low temperature BEEM/BEES measurement systems, which make it possible that the whole the measurement procedures from sample preparation to LT-MEEM/BEES measurements under ultrahigh vacuum.2.On preparation of novel surface semiconductor/magnetic materials nano-structures(1)We have investigated Fe deposition on GaAs(001) surface with various surface reconstructions, and find that 4x6 reconstructed surfaces give most reliable Shottky contact.(2)In order to clarify the properties of MnAs and CrAs crystallized in zincblende structures, which is expected to have half-metallic band structures based on first principle calculation, surface structure model of GaAs(001) covered with sub-monolayer MnAs was presented based on STM observat … More ions and LEED IV analysis.(3)In order to prepare iron silicide related semiconductor/magnetic materials surface nanostructures, Fe deposition on Si surface was investigated. It was found that Ag-terminated Si(111)√<3>x√<3>-Ag surface allow us to prepare Fe_3Si nano-dot having 10-20 nm in diameter.3.BEES observations of GaAs(001)/Fe Schottky contacts with different Fe layer thickness reveal that electron attenuation length in Fe layers is to be ranging from 1.52 to 2.74 nm depending on electron energy, which is fairly longer than previous reports.4.Careful examination of GaAs(001)c(4x4) surfaces by RHEED rocking curve and LEED IV analysis reveals that GaAs(00l)c(4x4) is not single structure, and have at least two similar but different structures. Furthermore it was demonstrated that phase transition between them can be taken place even at substrate temperatures as low as 300℃ and that confusing behaviors of low temperature MBE growth on GaAs(001)c(4x4) surfaces seems to be well accounted base on its multi-structure nature of c(4x4) surfaces. Less