- 學位論文
黑磷及二維材料電晶體之開發與黑磷及金屬接觸電極 之研究
Development of Black Phosphorus and Two-Dimensional Material Field-Effect Transistors and Investigation of Black phosphorus Metal Contacts
摘要
在摩爾定律即將面臨挑戰的時代，二維材料之材料特性的優勢使其成為未來可能替換掉傳統矽的材料。常見的二維材料包含石墨烯、過渡金屬二硫化物等等；而其中又以同時具備高載子遷移率與能隙的黑磷的材料特性較為突出。然而，金屬與黑磷的接觸電阻為限制其元件特性的重大議題，因此，本論文將研究如何降低黑磷的接觸電阻以及分析金屬與黑磷的介面特性。 本研究以機械式剝離法，將數層黑磷撕至二氧化矽基板上並以原子力顯微鏡及拉曼光譜分析黑磷之品質。並透過電子束微影的製程定義出源汲極，接著鍍上金屬，完成背閘極之黑磷電晶體。其電洞載子遷移率為340 cm2/Vs，並有103的開關比。另外也成功開發了二維材料異質結構堆疊的技術，完成以石墨烯為電極的二硫化鉬電晶體，其電洞載子遷移率為87.6 cm2/Vs，並有105的開關比。 為了降低黑磷的接觸電阻，我們以鍺作為黑磷電晶體的接觸金屬，在快速熱退火後成功地將鍺參雜入黑磷的源/汲極，退火後電洞遷移率最大可達227 cm2/Vs，載子遷移率增幅最大可達超過25倍，其接觸電阻可降低至0.365 kΩ∙μm，為目前文獻中的最低值。透過低溫量測的分析此接觸之金屬性，最後以X射線光電子能譜驗證了磷與鍺的鍵結。 為了分析鈦與黑磷的接面，我們透過活化能來萃取其蕭特基能障高度。經由理論的估計與穿隧電子顯微鏡的分析，我們發現此蕭特基能障高度為被低估的值。因此，我們改為利用接觸電阻的方法，成功的萃取出與理論較相符的蕭特基能障。 此研究可被高度應用在未來黑磷電晶體的發展，參雜鍺以降低接觸電阻的方式可應用於高頻及尺寸微縮，蕭特基能障萃取的方法可更廣泛的應用於不同金屬，能夠更精確地描述金屬與黑磷的接面關係。
並列摘要
In an era of post-Moore’s law, 2D materials become a promising platform for future electronic devices for their superior material properties. Although graphene and TMDs are the most discussed 2D materials, black phosphorus becomes more and more noticeable due to the high mobility and tunable band gap. However, the issue of contact resistance often limits the performance. Therefore, in this thesis, we will focus on the reduction of contact resistance and analysis of Schottky barrier height. We mechanically exfoliate few-layer BP onto SiO2 substrate and characterize the properties of BP flakes by OM, Raman spectroscopy, AFM. The back-gated BP FET is successfully fabricated, with an ION/IOFF of 103 and an extrinsic hole mobility of 340 cm2/Vs. A graphene contact MoS2 transistor by 2D heterostructure stacking graphene/MoS2/graphene heterostructure, and achieve an ION/IOFF ratio of 103 and extrinsic electron mobility of 87.6 cm2/Vs. Ge-doped S/D contacts of BP transistors are formed after RTA treatment. The mobility is enhanced by 25 times after RTA treatment. In addition, the contact resistance after RTA can be as low as 0.365 kΩ∙μm, which is the lowest value in literature and is comparable to III-V devices. Moreover, the PGex contact shows metallic properties, which is for the first time a metallic contact is shown in BP devices. XPS characterization further verify the P-Ge bonding after RTA. Schottky barrier height extraction of Ti-BP contact by activation energy method is also demonstrated. Through theoretical estimation and material characterization, an underestimated SBH is found which results from the hysteresis at higher temperature. Hence, a modified method is proposed by SBH extraction from contact resistance. A more accurate SBH is extracted, which can describe the Ti-BP contact more properly. The research in this thesis can be highly applied to BP devices in the future. Ge-doping technique can be applied to device scaling and high frequency devices, and SBH extraction can be applied to the analysis of metal-BP contact.
參考文獻
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