臺灣博碩士論文加值系統

本實驗以掃描光電流顯微術探討二維異質結構，異質結構以兩種層狀材料(SnS2/MoTe2)由機械式剝離法及乾式轉印技術在300nm的SiO2上構成，樣品A為Mote2在下SnS2在上，樣品B則為相反的結構，重合區域長寬約6*6μm2與6*3μm2，高約為各五層材料厚度，為經由電子束微影以及熱蒸鍍製作出鈦金電極(20nm/80nm)。

SnS2在背向閘極呈現n型傳輸行為，而MoTe2呈現雙載子傳輸行為，元件在Vds~1V時有超過4個數量極的開關電流變化，並且經由電流對閘極偏壓曲線，在Vds~1V時可以得到次臨界擺幅(SS)為1.7V/dec，也就是說當等效矽氧化層為5nm時可以達到28mV/dec的SS值，這是因為兩材料皆在次臨界狀態下運作，另一方面結合低溫實驗，可以發現其也存在熱游子運作機制。

經由掃描光電流顯微術搭配633nm雷射檢驗其光電流分布行為，633nm雷射只能激發MoTe2，其雷射解析度為1.5μm圓點，而光點每次可移動0.05μm的距離，結果可以發現其光電流主要分布在MoTe2與MoTe2/ SnS2異質結構之邊界，但主要在MoTe2之上，且可觀察到清晰的空乏區存在，並且可以知道MoTe2/SnS2為一typeⅢ對準的異質結構。

另外比較了MoTe2/SnS2/SiO2及SnS2/MoTe2/SiO2這兩個元件組合情況，其發現了兩者的MoTe2與異質結構的所形成的能帶結構應有所不同，其可能代表著兩者與基板有不同的電荷累積或捕捉現象。

We investigate two dimensional (2D) material heterostructures by scanning photocurrent microscopy.
The heterostructure consists of two different layered materials, SnS2 and MoTe2, and is formed by using mechanical exfoliation and dry transfer method on 300 nm SiO2. For sample A, MoTe2 is placed under SnS2; for sample B, MoTe2 is above SnS2. The overlapped region of samples A and B are about 6 × 6 μm2 and 6 × 3 μm2, respectively. The layer number of each material is about 5. The electrodes were made by e-beam lithography and thermal deposition of Ti/Au.

Under various back-gate biases, SnS2 is mostly n type and MoTe2 exhibits a bipolar behavior. The TFET device exhibits an ON/OFF ratio over 104 at VDS ~ 1V. The subthreshold swing (SS) obtained from the IDS-VGS transfer curve at VDS ~1V is about 1.7 V/dec, which is equivalent to about 28 mV/dec if the dielectric is scaled down to 5 nm. This is because the device operates in the region where both materials are gated in the subthreshold condition. From temperature dependent data, we found that the devices also inherit thermal activated transport properties.

We use a 633nm laser, which excites MoTe2 only, in scanning photocurrent microscopy to investigate the photocurrent distribution. The laser spot size is about 1.5 μm. The scanning step is 0.05μm. The photocurrent is most significant along the boundary of MoTe2 and MoTe2/SnS2 heterojunction and mainly on MoTe2 side. This indicates that there is a clear depletion region at this boundary and the MoTe2/SnS2 junction should possess a type III band alignment.

Comparing the transport and scanning photocurrent results of MoTe2/SnS2/SiO2 and SnS2/MoTe2/SiO2 heterostructure devices, we find that the band alignment between the bare MoTe2 and the heterostructure part is different. This could be caused by different charge trapping effect of the layer materials on the substrate for these two structures.

誌謝 i
摘要 ii
Abstract iii
目錄 iv
圖表目錄 vi
第一章 緒論 1
1-1前言 1
1-2 研究動機 4
第二章　實驗原理 5
2-1 MoTe2與SnS2基本介紹 5
2-2 MOSFET操作原理與電性 6
2-３電壓電流關係與位障 8
第三章 元件製作及量測系統 10
3-1基板介紹與清潔 10
3-2機械式剝離法 12
3-3轉印方式 14
3-4材料光學鑑定 16
3-5拉曼光譜鑑定 18
3-6原子力顯微鏡 19
3-7電子束微影與蒸鍍 21
3-8低溫電性量測平台 23
3-9打線接合與光電量測平台 24
第四章 結果與討論 26
4-1 各樣品製作成果 26
4-1-1各樣品光學影像 26
4-1-2樣品表面形貌 27
4-1-3材料鑑定 28
4-2樣品A量測 28
4-2-1樣品A電性量測結果 28
4-2-2樣品A光電流量測 34
4-2-3樣品A二次電性量測 38
4-3樣品B量測 39
4-3-1樣品B電性量測結果 39
4-3-2樣品B光電流量測 42
4-3-3樣品B二次電性量測 44
4-4樣品cd電性量測 45
4-5能帶結構分析 46
第五章 結論 50
第六章 參考資料 51
第七章 補充資料 56
7-1樣品A電性 56
7-2樣品A四線電性量測 56
7-3樣品A溫度相依電性量測 57
7-4樣品A光電流量測 59
7-5樣品B電性 60
7-6樣品B藍光光電流 61
7-7樣品B綠光光電流 62
7-8樣品B 長時間後電性 63

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