鍺矽氧和諧作用以精準操控鍺量子點移動與定位之研究;Precise control over Ge quantum dot migration and placement via cooperative interaction of Germanium/Silicon/Oxygen for quantum tunneling devices

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题名:	鍺矽氧和諧作用以精準操控鍺量子點移動與定位之研究;Precise control over Ge quantum dot migration and placement via cooperative interaction of Germanium/Silicon/Oxygen for quantum tunneling devices
作者:	陳冠宏;Chen,Kuan-hung
贡献者:	電機工程學系
关键词:	鍺;量子點;矽鍺;氧化;Germanium;quantum dot;SiGe;oxidation
日期:	2015-07-30
上传时间:	2015-09-23 14:45:37 (UTC+8)
出版者:	國立中央大學
摘要:	本文探討矽、鍺和氧原子之間的和諧互動機制，以精準定數和定位鍺量子點。首先，藉由矽鍺合金在高溫氧化的過程之中，會選擇性地氧化矽原子形成二氧化矽並且析出鍺原子的方法，我們可以製作出埋藏在二氧化矽中之鍺奈米晶粒。我們進一步發現在後續的高氧化或退火的製程之中，經由矽、鍺和氧之間的巧妙交互作用，可以有效地誘發已埋藏在二氧化矽中之鍺奈米晶粒的聚合成長、移動，甚至晶體形貌的變化。其中關鍵的因子有三:在鍺奈米晶粒的鄰近周遭是否有適量的含矽薄膜(或矽原子源)、是否有足夠的氧原子供應以及鍺扮演著催化劑的角色來協助鄰近含矽薄膜或矽原子源的局部氧化發生。經由實驗設計，我們發現在鍺量子點的表面存在有矽、鍺和氧彼此的競爭、破壞以及再重建的交互作用。若妥善運用此交互作用並加以設計，我們可以精準地掌控鍺量子點的成長熟化，進而控制其晶體形貌與大小，甚至設計含矽薄膜(或矽原子源)的位置以引導鍺量子點至指定之定點位置。矽、鍺和氧之間的互動反應簡述如下：在氧化矽鍺合金形成鍺奈米晶粒後，若鍺奈米晶粒的周圍有含矽薄膜或矽原子源，鍺原子會催化分解含矽薄膜的鍵結，使之釋放出矽原子。由於矽與鍺之化學親和力相近，被釋放的矽原子會快速地移動、貼近鍺奈米晶粒的表面，並進一步與鍺量子點表面的二氧化矽發生化學反應：Si + SiO2(s) 2SiO(g)，將二氧化矽分解成可揮發的SiO，並在鍺奈米晶粒前方形成空間孔洞。此空間孔洞提供了鍺奈米晶粒成長與移動的空間。此外，SiO亦可能移動到鍺奈米晶粒後方與外部提供的氧原子反應，再次形成SiO2。由於生成固體SiO2時，其體積約為原先的矽原子的2.2倍，此體積膨脹可以藉由推擠鍺奈米晶粒往前方的空間孔洞移動而獲得空間的舒緩。如此一來只要在有足夠的含矽薄膜(或矽原子源)與氧原子供應的環境下，可不斷地將鍺奈米晶粒往矽源的方向移動。值得一提的是，矽原子的釋放與否主要是透過鍺的催化來協助周遭的含矽薄膜(如氮化矽或純矽)發生局部的分解與氧化。因此除了鍺奈米晶粒與含矽薄膜之外，在鍺奈米晶粒/氮化矽薄膜界面是否有充分的氧足以促成局部氧化反應的發生是另一重要的關鍵因子。因為氧在二氧化矽與鍺內的擴散能力明顯有別。因此，在二氧化矽之中，若鍺奈米晶粒濃度或密度過高時，鍺奈米晶粒本身也會阻擋外部氧的擴散，導致在鍺奈米晶粒/緩衝氮化矽界面處無足夠的氧濃度，也就無法催化含矽薄膜(如氮化矽或純矽)局部的分解與氧化。如此一來，既無矽原子的釋放，也就無法誘發高密度鍺奈米晶粒的移動與成長。為解決此一問題，我們在高鍺含量的矽鍺合金和氮化矽緩衝層之間設計並插入了一低鍺含量的矽鍺合金薄膜。如此一來，不僅可有效地讓氧原子擴散到鍺/氮化矽表面誘發一系列的反應，也可藉由氧化高鍺含量的矽鍺合金來形成大顆的鍺球狀晶粒，達到有效掌控鍺晶粒尺寸的目標。基於以上的機制，我們將填入奈米溝渠或孔洞結構中的矽鍺合金氧化後，可以成功地製備球狀鍺量子點。而且藉由調整奈米溝渠或孔洞結構的幾何結構與尺寸大小，我們可以精準地在奈米溝渠或奈米孔洞中控制其位置與數量。當多邊形奈米孔洞的內切圓半徑大於15 nm，可以將鍺量子點置放在多邊形孔洞的角落或邊緣。當多邊形奈米孔洞的內切圓半徑小於15 nm，鍺量子點則會被引導到孔洞的正中心形成一個單一的量子點。使用這種方法，我們進一步地製作出量子點共振穿隧二極體。 ;This thesis investigates a cooperative mechanism that involves the participation and interaction of Si, Ge and oxygen interstitials for precise numbering and placing Ge quantum dots (QDs). First, using the method, selective oxidation of Si atoms then formation of SiO2 and separation of Ge atoms during high-temperature oxidation of SiGe layer, we are able to fabricate Ge QDs embedded SiO2. During high-temperature oxidation or annealing, we further observe the interaction of Si, Ge, and oxygen interstitials to facilitate the aggregation, growth and migration and even changing crystal morphologies of the Ge nanocrystallites. There are three key Factors： Whether the presence of the Si-containing layer (or source of Si) adjacent to Ge nanocrystallites, whether the presence of sufficient oxygen interstitials, and the local oxidation of Si-containing layer adjacent to Ge nanocrystallites by the Ge acting as a catalyst. We observe the interaction of competition, destruction, and reconstruction between Si, Ge, and oxygen interstitials at the surface of Ge nanocrystallites by the designed experiments. If we take advantage of the interaction, we would be able to precisely control the number, placement and crystal mophology of Ge nanocrystallites, furthur control the size and crystal morphology, ane even lead Ge nanocrystallites migratation to specified place by controlling the place of Si-conaiting layer (or source of Si interstitials). The interation of Si, Ge and oxygen interstitials is described briefly below：if the Si-containing layers (or the source of Si) are present near as-formed Ge nanocrystallites by oxidizing SiGe, the Si-containing layers would be decomposited and release Si interstitials by Ge acting as a catalys under thermal annealing in an oxidizing ambient. Because of their affinity for Ge, the Si interstitials first migrate to the surface of the Ge nanocrystallites where they facilitate the creation of voids in front of Ge nanocrystallites via the following reaction: Si(interstitial) + SiO2(s) 2SiO(g). The voids thus created, facilitate the growth and migration of the Ge nanocrystallites. Furthermore, SiO migrate behind the QD and react with O interstitials to re-form the SiO2. The volume of formation SiO2(g) is 2.2 times the original volume of Si interstitials. The stress of volum expansion is released by pushing Ge nanocrystallites into forward void. Thus, when the both sufficient Si and oxygen interstitials are supplied, Ge nanocrystallites would be able to continually migrate towards the source of Si interstitials by unceasingly destruction and construction. In particular, Si interstitials is released by Ge-catalyzed local oxidation and decomposition of the Si-containing layer (Si3N4 layer or Si layer). Thus, except Ge nanocrystallites and Si-containing layer, sufficient O2 which is supplied at the Ge nanocrystallite/Si3N4 layer interface is another key factor for facilitating local oxidation. The oxygen concentration is significantly reduced because of the Ge’s low affinity for oxygen and the low segregation coefficient of oxygen in Ge. Hence, the high-content or high-density of Ge nanocrystallites embedd SiO2 retard the diffusion of extern oxygen, and cause the insufficient concentration of oxygen at the Ge nanocrystallites/buffer Si3N4 layer interface, and result in Ge nanocrystallites can not catalyze the local decomposition and oxidation of Si-containing layer (Si3N4 layer or Si layer). Thus, there is neither releasing Si nor inducing the growth and migration of high-density Ge nanocrystallites. For overcoming this issue, we design and insert a low Ge-content poly-SiGe layers between high G-content poly-SiGe layers and buffer Si3N4. Thus, this method not only induce a series reaction by the oxygen effectively diffusing to Ge nanocrystallites/Si3N4 interface, but also form large Ge nanocrystallites by oxidizing high-content Ge poly-SiGe for effective controlling the size of Ge nanocrystallites. Based on the above mechanism, we oxidize the pre-filled SiGe in nanotrenches and nanocavities, and successfully form spherical Ge QD. Furthermore, we precisely control the position and number of Ge nanocrystallites by tailoring the sizes and geometries of pre-patterned nanotrenches or nanocavities. If the radius (r) of the incircle of nanocavity is more than 15 nm, Ge QDs are placed at the corner or side of nanocavities. If the radius (r) of the corresponding incircle of nanocavity is less than 15 nm, Ge atoms are led the cavity center and form a single Ge QD. Using this method, we further demonstrate quantum tunneling diode and observe clear Coulomb staircases and differential conductance oscillations at 77K
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