二維晶體異質結構之成長及其元件應用

Abstract

本論文以長出大面積的二硫化鉬及二硫化鎢為目標，使用了過渡金屬硫化法；此方法是在高溫下將過渡金屬(鉬或鎢)與硫蒸氣反應來形成大面積的薄膜；在成長參數最佳化的過程中，可以發現金屬薄膜在大氣下會先氧化，硫化時氧再被硫置換而形成我們要的二維材料；同時，本論文也指出了使用適量的硫粉對此成長方法的重要性。 使用最佳化後的成長參數，本論文展示了不同層數的二硫化鉬及二硫化鎢之薄膜特性，且成功地將兩個不同屬性的二維材料在同一塊基板上定位成長，並在最後，實現了二硫化鎢/二硫化鉬/二硫化鎢三層堆疊之雙異質結構。 另外，本研究也對二維晶體在電子元件上的表現做了深入探討，發現電流開關比、電子遷移率以及載子濃度都會受薄膜層數影響，選擇適當層數的二維晶體，所製成的元件才能發揮最佳的效用。

This thesis is about how to growth large area MoS2 and WS2 thin films by sulfurizing the transition metal directly. After the transition metal was deposited on the substrate, X-ray photoelectron spectrum shows that oxidation process occurred before sulfurization, which means that sulfurization process is a chemical process for sulfur atoms replaced by oxygen atoms. Also, according to Raman and photoluminescence spectrums, with proper sulfur powder amount, we can get high quality thin films. After optimizing the growth parameters, we can grow large-area MoS2 and WS2 thin films with controllable thickness. Moreover, with sulfurization process, we can decide the location of thin 2-D crystal films by selective metal deposition, which indicates that the selective growth of 2-D crystals is possible. Also, the WS2 / MoS2/ WS2 double hetero-structures was achieved, showing the possibility to create new material by stacking different kinds of 2-D crystals. As for electronic device application, we can also figure out that the electron mobility and drain current On/Off Ratio are dependent to the layer numbers of the 2-D crystal films .Choosing the suitable layer numbers is necessary to achieve the best performances of the devices.