Surface morphology evolution of Fe3Si on GaAs(001) and GaAs(111)A – Atomic layer-by-layer growth studied by scanning tunneling microscopy

電子自旋元件需要高效的將電子自旋注入半導體材料，其中製備高品質的鐵磁和半導體材料異質結構的結合是扮演著非常重要的角色。鐵三矽與砷化鎵擁有良好的晶格匹配以及鐵三矽用有43％的自旋電子極化率使鐵三矽與砷化鎵的結合成為了最佳化的異質結構。本篇論文中，單晶的鐵三矽藉由分子束磊晶的方式成長在砷化鎵（001）-4×6以及砷化鎵（111）A-2×2基板上，並且利用掃描穿隧式電子顯微鏡來分析表面形貌。藉由反射式高能量電子繞射得到高品質砷化鎵（001）-4×6以及砷化鎵（111）A-2×2的成長層。接著鐵三矽成長在砷化鎵表面上，藉由掃描穿隧式電子顯微鏡隨著不同厚度有系統的分析。鐵三矽在相同的長晶條件下成長在兩個不同晶面的表面，發現有不同的成長模式。透過掃描穿隧式電子顯微鏡得到鐵三矽在砷化鎵（001）-4×6上隨著厚度演變的表面形貌在定性上與先前論文中利用理論模擬得到的結果相似。在初始成長時，鐵三矽遵循島狀生長方式直到36.7埃，表面的顆粒才完全聯合在一起，而二維的層狀成長開始形成。在鐵三矽成長在砷化鎵（111）A-2×2中，一樣發現島狀成長出現於初始的成長過程。但二維的層狀成長出現在16.3埃較低的厚度。同時藉由理論計算表面的能量可以佐證在（001）及（111）晶面下成長會有不同的成長模式。High-quality hetero-junction comprises magnetic materials and semiconductors plays an important role in fabrication of spintronic devices which require high efficiency of spin injection into semiconductor for manipulations. Fe3Si/GaAs provides such an optimized hetero-structure in which the lattice is nearly matched and Fe3Si was found to have a spin polarization of 43%. In this work Fe3Si has been epitaxially grown on both GaAs (001)-4×6 and GaAs (111)A-2×2 by MBE and the in-situ scanning tunneling microscopy (STM) was utilized to characterize the surface morphology. Verified by RHEED, high-quality GaAs (001)-4×6 and (111)A-2×2 surfaces were obtained after the GaAs epi-layer growth. During the deposition of Fe3Si, the surface morphology was systematically studied by STM thickness-dependently. Different growth modes were observed between the Fe3Si films grown on the two surfaces with the same growth parameters. The STM investigation on Fe3Si/GaAs(001)-4x6 reveals a surface morphology evolution which is qualitatively consistent with a previous theoretical simulation; namely, the initial growth follows the Volmer-Weber (VW) mode up to 36.7 Å (13 ML), where the grains coalesced completely. Then, the two-dimensional layer-by-layer growth prevails. On the growth of Fe3Si/GaAs(111)A-2×2, the observed surface morphology follows the similar trend with the VW mode on the initial growth. However, a nearly layer-by-layer 2-dimensional growth mode was achieved in a much thinner film of 16.3 Å. Also the theoretical surface energy calculation supported the different growth mode occur in (001) and (111) plane