利用電子束轟擊二硫化鉬光感測器以提升激發光與光電流偏振選擇性

Abstract

本研究目的在於利用電子束轟擊單層二硫化鉬光感測器以調變能帶結構以達到區分左旋光與右旋光。在單層二硫化鉬動量空間中的第一布里元區的K與K'這兩個位置的能帶因價電帶上的電子自旋方向不同導致一個價電帶分裂成兩個能量不同的價電帶不同的價電帶上分別有自旋方向相反的電子，而為了要滿足動量守恆，不同自旋方向的電子只能吸收某個圓偏振方向的光，因此利用不同方向的圓偏振光可激發不同位置的能帶，而K與K'的能帶為直接能隙可放光，我們利用左旋光或右旋光激發單層二硫化鉬光感測器去偵測左旋光與右旋光光致發光的強度以及量測其激發光光電流，利用某個方向的圓偏振光其光致發光強度占總共偵測到的光致發光強度的比例計算圓偏振度，同理，利用某個圓偏振光光電流占總電流的比例計算光電流偏振度，比例越高代表區分左旋與右旋光的能力越強。我們利用電子束轟擊對單層二硫化鉬產生硫原子的缺陷，當我們轟擊適當的電子束濃度，產生適當硫原子缺陷濃度，可達到最高的偏振度。

The purpose of this study is to use an electron beam to bombard a single-layer molybdenum disulfide photodetector to modulate the energy band structure to distinguish between left-handed and right-handed circularly polarized light. The energy bands at the two positions K and K' of the first Brillouin zone in the monolayer molybdenum disulfide reciprocal space are divided into two parts with different energy due to the different electron spin directions on the valence band. Different valence bands have electrons with opposite spin directions on the valence bands, and in order to meet the conservation of angular momentum, electrons with different spin directions can only absorb light in a certain circular polarization direction, so the use of circular polarization in different directions light can excite the energy bands in different positions, and the energy bands of K and K' are direct band gaps that can emit light. We use left- handed or right-handed circularly polarized light to excite a single-layer molybdenum disulfide photodetector to detect left-handed and right-handed circularly polarized light. We measure the intensity of the photoluminescence of circularly polarized light and its excitation photocurrent, using the ratio of the circularly polarized light in a certain direction to the total detected photoluminescence intensity to calculate the degree of circular polarization. Similarly, use the ratio of the photocurrent of a circularly polarized light to the total current to calculate the degree of photocurrent polarization. The higher the ratio of the photocurrent polarization degree, the stronger the ability to distinguish between left-handed and right-handed circularly polarized light. We use electron beam bombardment to generate sulfur vacancy defects on a monolayer molybdenum disulfide. When we bombard an appropriate electron beam concentration to produce an appropriate sulfur vacancy defect concentration, the highest degree of polarization can be achieved.