探索TaS2電極對MoS2異質接觸場效電晶體之接觸電性

Exploring Electrical Contact Effects of TaS2 Electrodes on MoS2 Field-Effect Transistors

潘加恩(Chia-En Pan)

指導教授 ： 簡紋濱

國立交通大學/理學院/電子物理系所/碩士(2020年)

摘要

二維過渡金屬硫屬化合物 (Transition Metal Dichalcogenides)，具有合適的能隙與高載子遷移率的優勢，為近年來的熱門研究材料，但是目前的文獻中提到二硫化鉬(MoS2)場效電晶體其載子遷移率無法達到預期，其原因為當金屬與MoS2接觸後，其接觸電性能差而產生過大接觸電阻，使得載子於傳輸時受到阻礙，而限制元件的性能。我們參考以石墨烯作為接觸電極的實驗，利用少數層二硫化鉭(TaS2)取代傳統金屬電極製作MoS2場效電晶體元件，並探討傳統Ti/Au三維金屬與二維TaS2金屬電極，對二維材料MoS2形成不同的金屬接觸效應。
本實驗利用機械剝離法，將數奈米厚度的MoS2薄片轉移至矽基板上，並利用二維材料堆疊系統，將數奈米厚度TaS2薄片堆疊至MoS2薄片上方，後續再鍍上其它Ti/Au電極，製作成場效電晶體元件。本實驗特別於同一片MoS2薄片上比較TaS2與Ti/Au兩者不同金屬接觸，其接觸電阻與導致電性傳輸上的差異性，發現TaS2作為接觸電極，其接觸電阻比以Ti/Au作電極小。在電性傳輸方面，我們利用熱活化能傳輸與二維變程跳躍傳輸機制來分析載子傳輸行為，結果顯示以TaS2作為接觸電極，能提供低散射傳輸，其熱活化能 E_a 與特徵溫度{ T}_0，皆小於以Ti/Au作為接觸電極之元件，且所測量到的接觸電極降中系統無序性亦較低。在以TaS2作為接觸電極的場效電晶體元件上，我們控制閘極電壓調控並增加通道內載子濃度，觀察到金屬絕緣相變化行為，並針對臨界載子濃度與通道內電子交互作用力進行探討。

關鍵字

二硫化鉬 ； 二硫化鉭 ； 場效電晶體 ； 接觸電阻 ； 蕭特基位障 ； 金屬絕緣相變化

並列摘要

Because two-dimensional transition metal dichalcogenides (TMDs) have the advantages of a visible-light energy gap and a high mobility, they attract a huge attention in recent years. Among all TMDs, molybdenum disulfide (MoS2) is largely investigated in its field-effect behaviors. However, the experimentally demonstrated mobility of MoS2 based field-effect transistors (FETs) cannot reach the theoretically predicted high value. One of the most of the drawbacks could be the metal contact effects. The poor contact gives a high contact resistance to deteriorate the FET device performance. We refer to the experiment of graphene electrodes on MoS2 FETs and we pick up few layers of tantalum disulfide (TaS2) as electrodes for making MoS2 FETs. We plan to discuss the contact effect due to few-layer two-dimensional TaS2 flakes in comparison with traditional three-dimensional metal (Ti/Au) contact electrodes.
In this experiment, we transfer mechanically exfoliated MoS2 flakes on a silicon substrate and put TaS2 flakes on the top of the MoS2 flake by using the home-made stacking alignment system. Other Ti/Au metal electrodes are deposited to form MoS2 FETs. We technically put two TaS2 electrodes and two Ti/Au electrodes on the same MoS2 flake so as to study the TaS2 contact effect. It is found that the contact resistance of the TaS2 electrodes is much lower than that of the Ti/Au electrodes on MoS2 FET channels. We implement models of the thermally activated transport and the two-dimensional Mott’s variable range hopping to analyze electron transport behaviors. The results show that TaS2 electrical contacts always have a lower disorder in the contact. The thermal activation energy {(E}_a) and the characteristic temperature{ (T}_0) are all smaller for TaS2 contact than that of Ti/Au contact. Using the low disorder contact of TaS2 electrodes on MoS2 FET devices, we alternatively observe the metal-insulator transition when the carrier concentration of the MoS2 channel is raised up by increasing the gating bias voltages.

並列關鍵字

Molybdenum disulfide ； Tantalum disulfide ； Field-effect transistor ； Contact resistance ； Schottky barrier ； Metal-insulator transition

參考文獻

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