探討二硒化錸與黑磷異質結構之垂直式場效與雙極性電晶體

Vertical Field Effect and Bipolar Junction Transistors of ReSe2/BP Heterostructures

楊雅銓(Ya-Chuan Yang)

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

本實驗利用機械撥離法分離出厚度幾奈米的二硒化錸及黑磷，並透過二維層狀材料其獨特的結構組成，其表面乾淨平整且較少缺陷，利用凡德瓦力進行異質材料的堆疊，形成二硒化錸/黑磷/二硒化錸的垂直式場效及雙極性電晶體元件。透過場效電晶體電性檢測方式，可分別探索個別單一材料、兩種材料形成的異質接面以及三層材料所構成雙極性電晶體的電特性。
若探討單一材料，可觀察到二硒化錸及黑磷分別為n型導電傳輸機制與p型導電傳輸機制，考量場效電性表現、較高載子遷移率、高開關比而選擇此兩種材料。在異質接面方面，除原本材料的特性外，更在施加特定的背向閘極電壓下形成了具有整流特性的pn接面。由於兩種材料有不同電子親和力，在接觸熱平衡狀態下有一介面位障，透過電流電壓量測，在微小的順向偏壓及逆向偏壓下，載子透過直接穿隧進行傳輸；當順向偏壓逐漸增加後，載子將改以Fowler-Nordheim穿隧機制通過二硒化錸空乏區的位障抵達黑磷，形成傳輸通道；當順向偏壓加至一定程度後，載子將直接受電場吸引，形成漂移電流，此傳輸模式符合空間電荷限制電流傳輸。在雙極性電晶體方面，探討共射極的雙極性電晶體中扮演輸入端的基極電流與輸出端的集極電流與兩者所產生的電流增益，與一般雙極性二極體較為不同的地方在於由二維材料所組成的雙極性二極體可以利用背向閘極偏壓施加大小，影響共射極電流增益，由實驗觀察可知，在施加背向閘極偏壓表現高整流比特性時，將有較好的共射極電流增益。

關鍵字

二硒化錸 ； 黑磷 ； 直接穿隧 ； Fowler-Nordheim穿隧 ； 共射極電流增益

並列摘要

The mechanical exfoliation was used to isolate few-layer rhenium diselenide (ReSe2) and black phosphorus (BP) from their bulks. These two-dimensional (2D) materials possess atomiccaly flat surface and they can be easily stacked via van der Waals force to form ReSe2/BP/ReSe2 heterostructures of vertical field effect transistors (FETs) and bipolar junction transistors (BJTs) . Through field-effect measurements, we characterized electrical properties of each 2D material, the ReSe2/BP heterojunctions, and the ReSe2/BP/ReSe2 BJTs.
By applying back gate voltages, we confirmed that ReSe2 and BP are n- and p-type semiconductors, respectively. They both exhibited higher mobilities and high on/off ratios. As for the ReSe2/BP heterojunctions, we observed different rectification ratios under different back-gate voltges. Due to different vacuum energy levels of BP and ReSe2, there exists a built-in barrier when they forme a heterosture. With either a reverse bias or a small forward bias voltages, the current-voltage (I-V) curves can be analyzed well by the model of direct tunneling. With increasing forward bias voltages, the built-in barrier changes to a triangluar shape and the I-V curves agree well with the model of the Fowler-Nordheim tunneling. When the forward bias is much higher, the I-V curves follow the model of space charge limited current. As for the common-emitter BJTs, we focused on the current gain varied with the base and the collector currents. The BJTs made by 2D material have advantages of relatively higher mobilities and on/off ratios, and they presented a high current gain under the condition of a higher rectification ratio.

並列關鍵字

ReSe2 ； BP ； direct tunneling ； Fowler-Nordheim tunneling ； common-emitter current gain

參考文獻

[1] K. S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, Y. Zhang, S. V. Dubonos, I. V. Grigorieva, and A. A. Firsov. Electric Field Effect in Atomically Thin Carbon Films, Science 306, 666 (2004).

[2] R. R. Nair, P. Blake, A. N. Grigorenko, K. S. Novoselov, T. J. Booth, T. Stauber, N. M. Peres, and A. K. Geim. Fine Structure Constant Defines Visual Transparency of Graphene, Science 320, 1308 (2008).

[3] A. K. Geim and I. V. Grigorieva. Van der Waals heterostructures, Nature 499, 419 (2013).

[4] R. J. Toh, Z. Sofer, D. Sedmidubsky, and M. Purmera. 3R phase of MoS2 and WS2 outperforms the corresponding 2H phase for hydrogen evolution, Chem. Commun. 3054, 53 (2017).

[5] B. Jariwala, A. Thamizhavel, and A. Bhattacharya. ReSe2 : a reassessment of crystal structure and thermal analysis, J. Phys. D: Appl. Phys. 50, 044001 (2017).