對覆蓋式化學氣相層積生成公分級單層二硫化鎢使用於製作高靈敏光偵測器

Abstract

在本論文中我將探討大面積生長二硫化鎢的方式，以及其光激發光增強的現象，並將我們自己製備的二硫化鎢薄膜製成高靈敏的光感測器。 第一個主題是試圖找到一種大面積且高效率生長二硫化鎢方式，文中討論不同化學氣相層積方法，分別是傳統化學氣相層積和對蓋式化學氣相層積，並且討論對在不同表面能量的基板下生長的情形，最後透過預先層積氧化鎢薄膜在石墨片上，作為均勻前驅物的來源，並用鈉原子作為催化劑，成功提出了一種新穎的二硫化鎢生長方式，利用此方法可以一次生成七十平方公分由一百微米大的單晶組成的二硫化鎢薄膜。 第二個主題是探討由鈉作為催化劑生成的二硫化鎢光激發光增強的現象。我們發現由於生長過程中有鈉的參與，最後生成的二硫化鎢及基板中間有鈉的化合物，並輕微的參雜在二硫化鎢之中，因此導致二硫化鎢的複合機制改變，提高了載子複合效率，並且其光激發光強度超過機械剝離二硫化鎢的四倍。 第三個主題是我們利用自己製備的材料製成光感測器，由於單晶的尺寸大於一百微米，我們可以很輕易的將元件做在一個單晶之上，我們製作的二硫化鎢光偵測器響應度達4×〖10〗^5A/W，響應時間短於200微秒，這展現此光感測器的高工作效率。我們預期這個工作將對未來二維材料生長、應用及發展有重要影響。

In this thesis, I will discuss the large area synthesis of monolayer tungsten disulfide (WS2), its optical characterization and application to highly sensitive photodetectors. We first try to find a large-area and highly-efficient method for synthesizing WS2. The different chemical vapor deposition methods are discussed and a novel method is proposed where a pre-deposited tungsten film acts as a source of uniform precursor resulting in WS2 films that cover 70 square centimeters in one CVD step. We then investigate the optical characteristics of the thus produced material and observe a photoluminescence enhancement of WS2 generated by sodium catalyst (WS2-Na). The compound is slightly doped, thus causing a change in the recombination mechanism of the WS2 and improving the carrier recombination efficiency. The WS2-Na photoluminescence intensity is four times higher than that of mechanically exfoliated WS2. Finally, we use our synthesized WS2 to make photodetector. Since the size of the single crystal is larger than one hundred micrometers, we can easily make single-crystal devices. The WS2 photodetector we produced has a high performance with a responsivity that reaches 4×〖10〗^5A/W and response times that are shorter than 200 microseconds.