過渡金屬二硫族化合物(Transition metal dichalcogenides, TMDs)已然成為下一世代微縮奈米尺度電晶體及光電元件之前瞻二維半導體材料，其中又以二硫化鉬(MoS2)被視為最具潛力之材料。決定元件性能好壞其中至關重要的便是金屬與MoS2 之接觸界面，由於使用電子束蒸鍍(electron beam evaporation)製作 MoS2 元件電極時，高能量電子束易使金屬沉積於 MoS2界面產生熱損傷，進而引起大量缺陷，使費米能階釘紮在導帶(conduction band)附近，稱為費米能階釘紮現象(Fermi- level pinning)，致使元件應用受到影響。過去已有研究團隊提出使用轉印(transfer)金屬、選擇低熔點金屬當作電極等方式解決蒸鍍所造成的熱傷害。本研究為了降低傳統蒸鍍對 MoS2 所產生的熱損傷，引入了低溫電子束蒸鍍系統(low-temperature electron beam evaporation)，將金及白金沉積於單層 MoS2上，探討不同低溫金屬沉積參數對單層 MoS2 之影響。透過凱爾文探針顯微鏡(Kelvin probe force microscope, KPFM)及變溫量測系統觀察到在低溫 77 K 下蒸鍍金於MoS2，其蕭特基能障由常溫之 217 meV 增至 749 meV，實現了較高之蕭特基能障。電性量測結果表明，隨著金屬沉積溫度的降低，導通電流逐漸降低且臨界電壓(threshold voltage)從 18.8 V 往正偏壓位移至 55.8 V，與拉曼光譜(Raman spectroscopy)特徵A1g峰藍移了 3.7 cm−1結果相符合，顯示費米能階釘紮現象的減輕。 ;Molybdenum disulfide (MoS2) is regarded as the most promising material for two dimensional semiconductor applications. The critical factor determining the performance of these devices is the interface between metals and MoS2. However, conventional method of e-beam evaporation for fabricating device electrodes leads to thermal damage at the MoS2-metal interface, resulting in defects, strain and metal diffusion. As a consequence, the Fermi-level is pinned near the conduction band, a phenomenon known as Fermi-level pinning, which significantly affects the device′s performance. Previous researches have proposed solutions to mitigate the thermal damage caused by evaporation, such as using transfer methods for metals or selecting low melting point metals as electrodes. In this study, we aimed to reduce the thermal damage by introducing a low temperature e-beam evaporation system. We deposited high melting point metals gold and platinum onto single layer MoS2 and investigated the impact of different low temperature metal deposition temperatures. Through Kelvin probe force microscopy(KPFM) observations, we found that depositing Au at an extremely low temperature of 77 K led to the Schottky barrier height(SBH) increased from 217 meV to 749 meV. This demonstrated a reduction in the Fermi-level pinning phenomenon. Electrical measurements showed that with decreasing metal deposition temperature, the threshold voltage shifted from 18.8 V towards positive bias to 55.8 V. This observation was consistent with the 3.7 cm−1 blue shift in the A1g peak in the Raman spectroscopy results.
