以化學氣相沉積法製備之單晶二硒化鎢與其元件應用

Abstract

在本論文中，我們使用化學氣相沉積法成長單晶二硒化鎢薄膜，並且藉由控制薄膜成長溫度，可以得到最佳成長溫度為 950 ℃，接下來藉由控制氧化鎢粉的重量，可以控制單晶二硒化鎢的疏密程度，之後將最佳化之薄膜製作成上閘極式場效電晶體，由於氧化層不易沉積於二維材料上，因此對於氧化層沉積方面進行改進，我們先以電子槍沉積一層薄的氧化鋁，再使用原子層沉積氧化鋁，先以物理性沉積一層薄的氧化鋁在二硒化鎢表面上，利用這層薄的氧化鋁當中間層，使得 ALD 化學性沉積順利的成長氧化鋁，成功解決了過渡金屬硫屬化合物 (TMDs) 表面不易沉積氧化層的問題。接下來，我們探討二維結構的銻烯成長於單晶二硒化鎢上，在 120 ℃ 的製程條件下，成功的成長出二維結構的銻烯於單晶二硒化鎢表面上，銻烯薄膜層與層之間的間距經由量測為 3.8 Å，由於銻烯薄膜有著與石墨烯相當接近的片電阻，製程溫度又比石墨烯低了許多，故有著作為二維材料元件接觸電極的潛力。由於二硒化鎢與銻烯對於酸鹼性溶液抗性的不同發展出選擇性的蝕刻，我們將銻烯應用於二硒化鎢的上閘極式場效電晶體，與傳統鈦金電極的元件比較，很明顯汲極電流大幅度的上升，使電子遷移率也大大的提升，此證明了以二維金屬當作二維材料的接觸電極，可以有效的降低金屬電極與二維材料的接觸電阻。

In the thesis, we use chemical vapor deposition to do the experiments of single crystal tungsten selenide(WSe2) thin film. Compared with the results obtained from samples grown at different temperatures, the optimized growth temperature is 950 °C. Then, we have demonstrated that the density of the single-crystal WSe2 flakes can be controlled by the weight of the tungsten oxide powder. The optimized film is fabricated into the top-gate field effect transistor (FET). Because the 2D material surface is difficult to grow the dielectric layer, it is necessary to improve the growth conditions of the dielectric layer. We first deposited a thin layer of aluminum oxide (Al2O3) by using an electron gun evaporator, and then deposited a think Al2O3 layer by using the atomic layer deposition (ALD). The physically deposited thin Al2O3 layer would act as an interfacial layer between the WSe2 surface and the following think Al2O3 layer, which will ease the growth of the following chemically grown Al2O3 layer by using ALD. In this case, dielectric layers can be successfully grown on the surfaces of transition metal chalcogenides (TMDs). On the other hand, a well-stacked 2D material antimonene was grown on the single-crystal WSe2 at 120 °C. The layer separation between antimonene is 3.8 Å. Since the sheet resistance of antimonene is similar to graphene, it is possible to use antimonene as the contact metal of 2D material devices. Selective etching is developed by the acid and alkail resistance difference between antimonene and WSe2. We apply antimonene as the contact metals of top-gate WSe2 FETs. Compared to traditional titanium electrode devices, enhanced drain currents are observed for the device. The results have demonstrated that antimonene can effectively reduce the contact resistance between WSe2 and metal electrodes.