- 學位論文
探討石墨烯-過渡金屬二硫化物異質接面之電傳輸性質
Investigation on the Electrical Transport Properties of Graphene-TMDC Heterojunction
摘要
二維材料的成功製備為下一代的電子元件開啟新的可能性，但金屬與二維半導體的直接接觸往往會造成過大的接觸電阻，以至於二維材料元件的效能總是不理想。此外，由於二維材料特殊的物理性質，在自旋電子學研究上極具潛力。然而，接觸電阻必須落在最優範圍內，以得到顯著的磁阻效應。過大的接觸電阻將造成實現二維材料橫向自旋閥的困難。因此，必須先能有效降低二維元件的接觸電阻才能夠進行後續相關的研究。 在本研究中，我們製備石墨烯-過渡金屬二硫化物凡德瓦異質結構，並研究石墨烯層對其電性傳輸性質的影響。二維材料的製備是使用機械剝離法。此論文將呈現兩個樣品的結果: 第一部份中，我們探討多層二硫化鎢/數層石墨烯蕭基二極體。此樣品的製備是將二硫化鎢/石墨烯凡德瓦異質結構直接轉移至預先長好金電極的矽基板。我們發現石墨烯可以有效改善金與二硫化鎢間的接觸電阻。再加上特殊的樣品結構，使得樣品成為一特殊的閘極可調二極體；在第二部分，我們引入單層石墨烯到單層二硫化鉬與其金屬接觸之間，並探討電性上的改變。我們先將二維材料轉移到矽基板上，再使用電子束微影法寫出電極。此樣品採用鈷鐵做為接觸金屬，以期日後能夠基於此結構實現橫向自旋閥的應用。透過變溫實驗量測，我們發現加上石墨烯後的樣品其蕭特基能障高度明顯低於未加上石墨烯的對照樣品，代表接觸電阻可以被有效降低。 由上述的實驗結果，我們發現引入石墨烯能改善過渡金屬二硫化物與金屬之間的接觸，並有效降低接觸電阻。此對未來相關的電學或自旋電子學研究有所助益。
並列摘要
The successful preparation of two-dimensional materials (2DMs) opens up new possibilities for the next generation of electronic applications. While direct contact between metal and 2D semiconductors often results in excessive contact resistance, lowering the performance of 2DMs devices. Besides, because of the unique physical properties of 2D materials, they have great potential for spintronics researches. However, the contact resistance need to locate in an optimized regime to acquire significant magnetoresistance effect. Excessive contact resistance will also make it difficult to realize lateral spin valve based on 2D materials. Therefore, the contact resistance of 2D devices must be effectively reduced before the subsequent related research can be performed. In this work, we fabricate graphene-TMDC Van der Waals heterostructure and study the impact of graphene layer on the electrical transport properties. 2D materials are prepared using mechanical exfoliation. The results of two samples will be shown in this thesis: In the first part, we study the multilayer tungsten disulfide (WS2)/ few layer graphene Schottky diode. This sample was prepared by directly transferring a WS2/ graphene Van der Waals heterostructure to a 300nm/ P++ Si substrate, on which gold electrodes were deposited in advance. We found that graphene can effectively improve the contact resistance between gold and WS2. Coupled with the special sample structure, the sample shows a special gate-tunable diode characteristic; In the second part, we introduce a graphene mono-layer between a molybdenum disulfide (MoS2) mono-layer and its metal contact, studying the change of electrical properties. For this sample, we first transferred 2D materials onto a 300nm/P++ Si substrate and then wrote the electrodes by e-beam lithography. Cobalt iron (CoFe) was used as the contact metal in order to lay the foundation for further realizing the lateral spin valve applications based on such kind of structure. Through temperature-dependent measurement, we found that the Schottky barrier height of the sample with graphene interfacial layer was significantly lower than that of the control sample without graphene, indicating that the contact resistance could be effectively reduced by inserting graphene interfacial layer. From our experimental results, we reveal that introducing graphene is able to improve the contact between metal and TMDC materials, effectively reducing the contact resistance. It should benefit the further related researches, both in electronics and spintronics.
參考文獻
延伸閱讀
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