|摘要: ||此篇論文研究之目的為探討多層釩/氧化鋅(氧化鋅鋁)之高遷移率以及高載子濃度的導電行為。在固定的釩摻雜濃度下, 藉由拆成不同層數及厚度的釩於氧化鋅(或氧化鋅鋁)薄膜中來探討載子提供層(氧化鋅/氧化鋅鋁)與載子傳輸層(釩)間的電子傳遞機制。由實驗得知，過低或過高層數的多層釩/氧化鋅(氧化鋅鋁)皆無法得到最佳的電性表現, 然而在3×4的結構且厚度分別為63 Å及453 Å之多層釩/氧化鋅(氧化鋅鋁)獲得最低的電阻率及最高遷移率。藉由光激螢光光譜PL配合紫外光電子光譜UPS，本研究可得知高遷移率的主因並非來自於介面的二維電子氣2DEG, 而是釩層中的特定相。藉由光電子能譜儀XPS分析，此特定相在高溫熱處理時會形成特定的高遷移率釩鋅氧混相ZnVxOy*, 且在形成的同時,部分氧化鋅(氧化鋅鋁)內的氧原子由於釩層的氧化而被吸引至釩層, 導致氧化鋅(氧化鋅鋁)內由於化學劑量數的不平衡而形成帶有氧空缺的組成, 進一步提供了自由載子的來源。|
對於多層釩/氧化鋅(氧化鋅鋁)薄膜導電機制，本研究利用不同夾層數的結構分析電性的變化，本研究得知(1) 當夾層數高於3×4時最高遷移率開始下降, 而在氧化鋅鋁中更為顯著；(2)總釩層相同的情況下, 各別分開且具有一定厚度的釩層會有較高的遷移率表現。本研究提出低載子濃度的高載子傳輸層, 將形成寬大的Debye電場, 吸引相鄰載子提供層內的自由電子進入載子傳輸層, 進行高速的載子傳遞。此外，本研究推測當載子傳輸層之間的距離開始接近以至於彼此形成的Debye電場開始重疊時, 部分Debye電場將會互相抵銷以致Debye電場的吸引力削弱。此機制亦可解釋低載子濃度、高遷移率的超薄載子傳輸層為何可以如此大幅度的提升異質結構整體的遷移率。;In this study, the conducting mechanism of high mobility and high carrier concentration of multilayer V:ZnO (AZO) were discussed. In Chapter 1, according to the literatures, the uniform doping shows the poor enhancement of the conductivity owing to the impurity scattering with dopants. Thus, the modulated doping method has drawn lots of attention recently, because the heavily-doped films provide the charge carreris, and the transportation occurs in the low-doped layers of the stack that are not subjected to limit the mobility by the ionized impurity scattering. In Chapter 2, the electrical properties of V:ZnO (AZO) multilayer thin films were studied. The 3×4 V:ZnO (AZO) thin films with V (63 Å) and ZnO (453 Å) layers exhibits the lowest resistivity with a high mobility. Analysis of PL and UPS spectra show that the high mobility path is the certain phase in the V layer. It is not the high mobility 2DEG near the V/ZnO (AZO) interfaces. XPS analysis verified that the certain phase of ZnVxOy* in the V layer would form under specific annealing temperature. Part of the oxygen in ZnO (AZO) would be drawn into the V layer owing to the oxidation of V. This stoichiometric defects of the oxygen vacancies in the ZnO layer provides the excess free carrier source.
In Chapter 3, the variation of electrical properties in several different structures of V:ZnO was used to study the conducting mechanism. Two key findings: (1) the mobility of each multi-layer structure starts to drop, as the number of the layer in the multi-layer structure is higher than 3×4. The phenomenon is even prominent in V:AZO thin films. (2) the thickness of V breaking down to thin V layers displays a higher mobility. The wide Debye electric field originated from a low carrier concentration and a high mobility transport layer will draw the carriers in the neighboring donor (ZnO) layer into the transportation (V) layer to proceed a high speed transit. Besides, as the distance between the each transport (V) layer starts to get closer with the result that the Debye electric field starts to overlap, then, partial Debye electric field will be neutralized by each others and leads to the elimination of Debye electric force. This mechanism explains how does a low carrier concentration and a high mobility ultra thin transport layer make such an immense effect on the improvement on the entire mobility by attracting the carriers from the donor layer, in which the mobility is limited.