合成兩極性大面積單晶二硒化錸用於近紅外光發光二極體之應用

Abstract

過渡金屬二硫化物由於其顯著的光學和電學性質，而在光電應用的二維半導體材料領域中獲得了各方研究學者極大的興趣。而在此領域中，具有寬廣的發射能譜的有機發光二極體已是當今二維半導體材料領域應用的主流。然而，有機物質低結晶性的特性、PN結中間的位能障蔽、在電極附近的電荷載流子的積累以及有機發光二極體必須用高驅動電壓的缺陷，皆直接或是間接抑制了電子－電洞的結合效率，導致強激子湮滅與低強度放光。在最近以過渡金屬二硫化物為主的發光二極體的報告中，其通道材料（例如二硫化鉬，二硒化鎢與黑磷）具有高結晶性和低驅動電壓的性質，並且可利用閘極調整的兩極性場效特性；但是它們的兩極性場效特性對於材料層數的依賴性以及金屬電極附近的載流子積累已成為光電應用中的主要憂慮的重點。 在本項研究中，我們透過使用二硒化錸（ReSe2）此種兩極性過渡金屬二硫化物作為通道材料，構築不對稱電極的近紅外線發光場效電晶體。二硒化錸是晶格低對稱的兩極性層狀材料並且具有直接能隙，其能隙幾乎與層數無關。我們使用了可合成高品質的兩極性二硒化錸單晶的化學氣相沉積技術，並通過拉曼光譜，光致發光光譜，X射線電子能譜（XPS），能量色散X射線能譜（EDS）和高解析度穿隧式電子顯微鏡（HR-TEM）來鑑別合成後的ReSe2晶體。我們對於其發光場效電晶體進行電流性質的測量，也得出了兩極性的電子傳輸性質，而此結果於未來將進一步用於開發近紅外發光二極體之應用。

Transition metal dichalcogenides (TMDs) have gained tremendous interest in the field of two-dimensional materials for optoelectronic applications owing to their remarkable optical and electrical properties. Numerous organic light-emitting diodes (LEDs) with emissions in wide spectral ranges have been used extensively. However, the low crystallinity of constituent materials, the potential barrier across the p-n junction, the accumulation of charge carriers in the vicinity of electrodes, and the high drive voltages in these organic LEDs suppress the electron-hole recombination efficiency, leading to strong exciton quenching and low luminescence. In the recent reports of TMD-based LEDs, the constituent materials (such as MoS2, WSe2, and black phosphorus) are of high crystallinity with low potential barrier and have gate tunable ambipolar field-effect behavior, but their layer-dependent ambipolar nature and the carrier accumulation in metal electrodes to induce gap states have become a major concern in optoelectronic applications. In this study, we explored a novel light-emitting transistor (LET) by using the ambipolar TMD of rhenium diselenide (ReSe2) as a channel material with asymmetric metal electrodes for an infrared LED. ReSe2 is an ambipolar layered-material of low symmetry and has a direct bandgap, which is nearly independent of the layer thickness, i.e., with only a minimal change in the bandgap by thinning the layered ReSe2 crystal from bulk to monolayer. Here, we present the chemical vapor deposition (CVD) growth of high-quality ambipolar ReSe2 single crystals. The as-synthesized ReSe2 crystals were characterized by Raman, photoluminescence, X-ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy (EDS), and high-resolution transmission electron microscopy (HR-TEM) to show their structural and compositional characteristics. The electrical measurements of the as-fabricated ReSe2-LET have showed the ambipolar characteristics of the devices, which will further be used to develop a near-infrared LED.