自旋電子學是利用載體（電子與電洞）自旋傳導的電子學，而載體傳導的自旋動力學與磁性光電元件的發展息息相關。半金屬材料的特性是在費米能階只存在某一自旋方向的電子態密度，只有帶此特定自旋方向的電子可以傳導，因此被認為在自旋電子學的應用上極具潛力。鐵磁性材料Fe3Si的居禮溫度(Curie Temperature)為840K，且具有特殊Heusler alloy結構，由於Heusler alloy被認為具有半金屬特性，Fe3Si/GaAa異質結構可能可以在自旋電子學的應用上提供較高的自旋注入效率。
在這個論文裡，我們利用分子束磊晶系統成長出磊晶薄膜，Fe3Si薄膜磊晶過程由高能電子繞射(RHEED) 量測分析得到銳利的條狀圖案。利用高解析X-光繞射儀，我們得到Fe3Si薄膜布拉格繞射條紋的rocking curve半高波寬約為0.014°，也得到Fe3Si和GaAs之間的晶格係數差異約為-0.2%，因此，我們可以得到晶格係數幾乎相配的Fe3Si/GaAs系統。我們利用SQUID得到Fe3Si的磁滯曲線，發現曲線隨著成長溫度不同有些變化，為了改善可能產生的介面作用層，我們設計了一種新的成長方式。除此之外，我們也利用in-situ X-光光電子能譜儀發現經過in-situ高溫退火之後介面作用層成功的被減少。
利用分子束磊晶系統，我們也成功的在GaAs (100)基板上長出磊晶薄膜MgO。利用X-光繞射量測，我們發現單晶MgO和GaAs是以4:3的晶格匹配。因此，我們可以利用磊晶的MgO薄膜作為穿隧能障，繼續研究Fe3Si/MgO/GaAs系統的穿隧自旋注入效率。

Spin dependent transport of charges is critical to the functionality of many magneto-electronic devices. Since half metals have electrons of only one spin state present at the Fermi energy, they are ideal candidates to be used as spin injectors. Fe3Si is a ferromagnet with a Tc of 840K, and can be regarded as a Heusler alloy with a composition of Fe2FeSi. Fe3Si is recently considered as an excellent candidate for spin injection, since some of the Heusler alloys are predicted to be half metals with 100% spin polarization.
In this work, the epitaxial film growth was carried out in a multi-chamber MBE system. Streaky RHEED patterns were observed during the MBE growth of Fe3Si on the atomically flat GaAs(100) surface. High-resolution x-ray diffraction measurements were made on our Fe3Si films and gave a narrow rocking curve of about 0.014°. The lattice mismatch between the film and GaAs was determined to be of about -0.2%. Hence, it was feasible to obtain a perfectly lattice matched epitaxial heterostructure for studying effective spin injection. The magnetic properties were measured at 10K and 300K by SQUID magnetometry. The B-H loops at low fields showed fine features that varied with film growth temperature. The appropriate growth procedure was then carried out to minimize the interface reactions. Otherwise, the in-situ XPS spectra showed that the interfacial Fe–Ga–As reactions were reduced by annealing at higher temperatures.
MgO was also successfully grown on GaAs (100) substrate. It was obtained using x-ray diffraction measurement that the single crystal MgO was epitaxially grown on GaAs with a 4:3 lattice coincidence. Hence, it was possible for us to study Fe3Si based tunnel spin injector using an epitaxial MgO as a tunneling barrier.

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