Investigation of carrier spin related phenomena in Si and its application to spin-functional devices

本研究的最终目标是实现利用载流子电荷和载流子自旋自由度的自旋金属氧化物半导体场效应晶体管（自旋mosfet）。由于自旋MOSFET的工作原理是在MOS反转Si沟道中自旋相关输运，因此迫切需要具有低肖特基势垒高度的铁磁材料。在本研究中，采用了两种不同的方法：（方法1）离子注入，（方法2）在铁磁材料晶体生长过程中的自掺杂效应。在方法1中，通过硅化在Si（001）衬底上制备铁磁性FeSi。为了降低硅化温度，进行了能量为15eV的As原子离子注入。结果表明，低温形成的FeSi/Si结对电子具有较低的肖特基势垒高度。在方法2中，发现生长在Si（001）上的MnAs具有较低的电子肖特基势垒高度，这是由于在分子束外延的初始阶段自动掺杂了As。我们用MnAs制备了自旋mosfet，发现自旋mosfet在50K以下表现出迟滞行为，这可能源于自旋相关输运。

The final goal of this study is to realize spin metal-oxide-semiconductor field-effect transistors (spin MOSFETs), which utilize carrier charge as well as carrier spin degrees of freedom. Since the operation principal of a spin MOSFET is spin dependent transport in a MOS inversion Si channel, ferromagnetic materials with a low Schottky barrier height are strongly needed. In this study, two different methods were used : (method 1) ion implantation, (method 2) auto-doping effect during the crystal growth of a ferromagnetic material. In method 1, ferromagnetic FeSi was fabricated through silicidation on a Si(001) substrate. To reduce the silicidation temperature, ion implantation of As atoms with a energy of 15eV were performed. As a result, we demonstrated that FeSi/Si junctions formed with a low temperature have a low Shottky barrier height for electrons. In method 2, MnAs grown on Si(001) was found to have a low Schottky barrier height for electrons, which is due to the auto-doping of As during the initial stage of molecular beam epitaxy. We fabricated spin MOSFETs with MnAs, and found that the spin MOSFETs exhibit hysteretic behavior below 50K, which probably originates from spin-dependent transport.