利用配體修飾量子點結合二維材料之高響應混合型光偵測器

Abstract

本論文主要探討PbS 量子點結合二維材料之混合型光偵測器，藉由量子點的高吸收結合二維材料的高載子遷移率，來達到高響應率的光偵測器，而不同配體置換的PbS 量子點也會影響量子點與二維材料之間的載子傳輸。 第一部份探討了不同配體置換的量子點與石墨烯混合型光偵測器，首先我們要對PbS 量子點進行配體置換，由於量子點在合成過程中會加入長碳鏈油酸避免量子點彼此聚集，而長碳鏈油酸會阻礙量子點間的載子傳導，因此以短配體置換油酸以增加其導電性，藉由傅氏轉換紅外光譜(FTIR)和X 射線光電子能譜(XPS)驗證是否將油酸完全置換成短配體，且不同短配體的置換會造成真空能階的偏移，因此對於石墨烯會有不同的摻雜效應，因此在光偵測器上的表現有所差異。以MPA、TBAI、EDT、PbI2 這四種配體做修飾，實驗結果得到以MPA 置換的元件(PbS_MPA/graphene)表現最好，其響應率可達5.36 × 106A/W。 第二部分則是以 PbS 量子點結合二硫化鉬 (MoS2) 的混合型光偵測器，以單純化學氣相沉積法所成長的單層MoS2 在成長過程中產生較多的硫缺陷，使光偵測器在響應時間上表現得較慢，而我們以硫醇分子置換PbS 量子點同時硫醇分子也能填補MoS2 的缺陷，使元件響應時間變快；不只改善了響應時間，同時高吸收的量子點材料也使響應率大幅提升。

In this thesis, the hybrid photodetector based on PbS quantum dot (QD) and twodimensional materials (TDMs) had achieved high gain and high responsivity optoelectronic characteristics due to the strong absorption of QD and high mobility in TDMs. Carrier transport between QD and TDMs would be efficient by various ligand passivation. In the first part, the hybrid photodetector PbS QD with different ligand passivation combined with graphene was performed. In the synthetic process, the long alkyl chain would be used to capped the surface of PbS to prevent quantum dot aggregation, but the long alkyl chain of oleic acid capped PbS will block inter-dot carrier transport. To overcome this, ligand exchange was needed to replace the long alkyl chains with short ligands to improve the conductivity. Fourier transform infrared spectroscopy(FTIR) and X-ray photoemission spectroscopy (XPS) was available to verify whether the oleic acid is completely replaced. Also, various ligand passivation lead to the vacuum level shift, and the phenomenon would interpret the graphene doping effect. We used four different ligands such as MPA, EDT, TBAI and PbI2 to passivate PbS QDs. The experimental results validated that the MPA-PbS /graphene hybrid photodetector had achieved the best responsivity up to 5.36 × 106A/W. In the second part, the hybrid photodetector based on PbS and MoS2 was fabricated. The CVD monolayer MoS2 had lots of defect, which caused the slow response time. The thiol molecules was used to passivate the surface of PbS QDs and also fill the defects of MoS2. The passivated PbS combined with MoS2 is not only improved the response time but also efficiently enhance the responsivity due to the high absorption of PbS QDs.