矩形黑磷薄膜電晶體其光電特性的各向異性

Abstract

黑磷為一種具有高電洞遷移率以及直接能隙(= 0.33eV) 的二維材料。影響其載子遷移率的因素包括了黑磷薄膜的厚度、contact金屬的選擇以及載子移動的方向。因此必須同時考慮這三個因素，才有辦法達到黑磷薄膜電晶體的高電洞遷移率。 本論文首先對黑磷的基本性質做了材料分析。透過光學顯微鏡以及原子力顯微鏡的搭配可以粗略的判斷黑磷薄片的厚度，拉曼光譜儀則能夠用來辨認黑磷薄片的晶體方向。X射線與極紫外線光電子能譜儀則可用來確認黑磷與金鍺合金元素組成、能隙與功函數。透過挑選適當的厚度、使用金鍺合金來達成歐姆接觸、以及製作長方形黑磷來迅速判斷黑磷晶格方向，成功製造出擁有良好元件特性的背電極黑磷薄膜電晶體，其元件表現出接近300cm2/V*s的場效電洞遷移率和高達3個數量級的電流開關比。同時也製作了黑磷-二硫化鎢的異質接面整流二極體與透過厚度控制達成的黑磷同質接面整流二極體，兩者接近2的理想因子顯示其電流主要為復合電流主控。兩者良好的光響應則展現了具有直接能隙的黑磷在光電應用上的潛力。

Black Phosphorus (BP) is a 2D material with high hole mobility and direct bandgap ( = 0.33eV). The factors that will influence its carrier mobility are thickness of the BP thin film, choose of the contact metal and the transport direction of the carriers. Therefore, these three factors must be considered simultaneously to obtain the high hole mobility of BP thin film transistors. In this thesis, material analysis is first conducted to study the fundamental properties of the exfoliated BP. The thickness of BP flakes can be roughly determined by optical microscopy and atomic force microscopy (AFM). The lattice orientation of BP flakes can be recognized by Raman spectroscopy. X-ray and Ultraviolet photoelectron spectroscopy are used to measure the elemental composition, bandgap and work function of BP and AuGe alloy. Through picking the appropriate thickness of the BP thin film, using AuGe alloy to obtain ohmic contact, and fabricating rectangular BP thin film to determine the lattice orientation of BP flakes, the back-gated BP thin film transistors (TFTs) are successfully fabricated and show excellent device performance. The high hole mobility near 300cm2/V*s and the on/off ratio up to 3 order of magnitude can be achieved. The P-N BP/WS2 heterostructure and BP homostructure through thickness engineering are also fabricated. Both of their ideality factors are near 2, indicating that the forward current is dominated by recombination current. Their good optical responsivities also show BP’s potential in the application of optoeletronics due to its direct bandgap.