二硒化鎢薄膜電晶體光電特性研究

Abstract

本論文證明了在氧氣環境中快速熱退火能提高多層二硒化鎢 (WSe2)薄膜電晶體之性能。實驗結果顯示，氧氣退火處理後，場效遷移率可以從1.49增加到31.1 cm^2 / Vs。開/關電流更高達10^7。且使用二維結構之六方氮化硼 (h-BN)作為基板以及保護層來觀察吸附在通道上的氧。除此之外，藉由量測拉曼光譜以及XPS的變化證實退火後氧氣以及p摻雜效應的存在。根據上述的結果，吸附在通道頂部以及底部的氧分子都對WSe2電晶體的性能產生了影響。因此，這項研究提供了一種改善WSe2電晶體元件性能的方法，並將雙載子傳輸轉變為單載子，這對於CMOS邏輯電路的應用是很重要的。 此外，我們發現WSe2厚度相關的特性並用來製造不對稱WSe2同質結構的p-n二極體，調變厚度來改變pn特性。結果顯示，理想因子為1.64，整流比約為10^3。對於光學性能，採用650 nm雷射作為光源。最佳填充因子，光響應度以及EQE分別為45.7％，16.02 mA / W和3.06％。因此，我們實現了同質結構光探測器且具有良好的光電學性質，未來能應用於探測器，開關，太陽能電池等。

In this study, high-performance multilayer WSe2 filed-effect transistors were demonstrated by rapid thermal annealing process in oxygen ambient. The experimental results indicate that the field-effect mobility of hole could be enhanced from 1.49 to 31.1 cm^2/Vs after oxygen annealing treatment. The on/off-current ratio will up to so high as 10^7. It’s also used 2D-layered hexagonal-boron nitride (h-BN) as substrate or passivation layer to observe the absorbed oxygen on the channel. Additionally, it confirmed the existence of oxygen and p-doping effect after annealing treatment by measuring Raman spectra and XPS. According to the above results, both oxygen molecules on the top and at the bottom of the channel have the dramatic influence on the WSe2 TFTs’ performance, and, moreover, this work provides a method to improve the device performance of WSe2 TFTs and change the undesirable ambipolar transport to the unipolar, which is essential to the implementation of CMOS logic. Moreover, the WSe2 homostructure rectifying diode is demonstrated, p-type and n-type WSe2 regions were formed by adopting different layer WSe2 thicknesses. Typically, the common way to fabricate two-dimensional material based diode is to use heterostructure by stacking two different carrier type and band gap energies materials. However, there is always lattice mismatch at the junction, leading to the degraded photoresponse of the diodes. In order to reduce the problems of heterostructure diode, layer thickness dependent band gap energy of WSe2 is reported and applied to fabricate homostructure diode. The ideality factor of the current-voltage characteristic is 1.64 and the current rectification ratio can reach to 10^3. The optical properties of the diode, including fill factor 45.7%, responsivity 16.02 mA/W and EQE 3.06% are reported. It is concluded that the WSe2 homojunction diode can be applied in photodetectors, switches, solar cells etc.