使用第一原理計算SiC/SiO2核殼奈米線光致發光光譜中的峰值和鐵酸鉍摻雜釹漏電流的第一原理詳細分析

Peak emission intensity in photoluminescence spectrum of SiC/SiO2 core–shell nanowires using first-principles calculations and the detailed analysis of leakage current in Nd-substituted BiFeO3 through first principles calculations

徐嵩閔(Song-Ming Hsu)

指導教授 ： 歐陽淳厚 (浩)

國立清華大學/工學院/材料科學工程學系/碩士(2021年)

摘要

第一部分
根據陳柏宇學長製作的碳化矽(SiC)奈米線(NWs)，以及其光致發光(PL)光譜的藍移特徵，並基於樣品的STEM圖製作~1.5 nm 3C-、~1.0 nm 2H-、~1.0 nm 4H-和~1.5 nm 6H-SiC奈米線結構。堆垛層錯(SFs)會導致3C-SiC在局部產生類2H-、4H-和6H-SiC的堆疊排列，SiC奈米線PL光譜中藍移強光的來源通常被歸因於堆垛層錯，但是源於何種局部結構卻少有討論。本研究基於穿透式電子顯微鏡(TEM)影像建構沿[111]方向的3C-和沿[0001]方向的2H-、4H-和6H-SiC奈米線，並通過模擬來確定PL光譜中藍移強峰的來源。對NWs的計算結果表明，直徑為1.42 nm的3C-SiCNW的能隙為3.427 eV，此結構與最強的發射光的能量最接近。接面計算表明，隨著能量的增加，電荷將從SFs轉移到納米段內部。
第二部分
根據彭憶婷學姊製作的鐵酸鉍摻雜釹增強光伏效應的研究，本研究利用第一性原理計算來研究 鐵酸鉍(BFO)摻雜釹漏電流降低的機制。鐵酸鉍和摻雜釹的鐵酸鉍(BNFO)的狀態密度(DOS)可以在能隙中產生深陷阱態，陷阱電離能分別為 ~0.60 和~0.72eV。由於摻雜釹，BFO的漏電流隨著電離能的增加而降低。光學性質計算的結果還表明，BNFO在紅光至黃光範圍內具有更高的吸收率和更低的能量損失。從上述分析結果來看， BNFO在光伏電池的應用方面具有優勢。

關鍵字

第一原理 ； 碳化矽 ； 光致發光 ； 鐵酸鉍 ； 漏電流

並列摘要

Part 1
According to the silicon carbide (SiC) nanowires (NWs) made by Chen Bo-Yu. The blue shift characteristics of its photoluminescence (PL) spectrum, and based on the STEM image of the sample, make ~1.5 nm 3C-, ~1.0 nm 2H-, ~1.0 nm 4H- and ~1.5 nm 6H-SiC nanowire structure. Stacking faults lead 3C-SiC to locally produce 2H-, 4H- and 6H-SiC-like stacking arrangements. The source of blue-shifted strong light in the PL spectrum of SiC nanowires is usually attributed to stacking faults, but the local structure of the source is rarely discussed. This study constructs microstructures of 3C- along the [111] direction, and 2H-, 4H-, and 6H-SiCNWs along the [0001] direction based on the transmission electron microscope (TEM) micrographs and identifies the source of the strongest peak in the PL spectrum through simulations. The results of our calculations of the NWs show that the bandgap of 3C-SiCNWs with a diameter of 1.42 nm was 3.427 eV and this structure was related to the strongest emission. The interfacial calculations indicate that the charge will be transferred from the stacking faults (SFs) to the inside of the nanosegment as the energy increases.

Part 2
Following the work of “Remarkably enhanced photovoltaic effects and first-principles calculations in neodymium doped BiFeO3” by Y.T. Peng et al. This study uses first-principles calculations to study the mechanism of reduced leakage current due to in the Nd-substituted case. Our simulations indicate that the density of state (DOS) of BiFeO3 (BFO) and Nd-substituted BiFeO3 (BNFO) can generate a deep-trap states in the band gap, and the trap ionization energies is are ~0.60 and ~0.72eV, respectively. The leakage current of BFO is reduced as the ionization energies increase due to the adding of Nd. The results of optical properties calculations also showed the higher absorptions and lower energy loss in the range of red to yellow light in BNFO. From results of analyses mentioned above, where BNFO is advantageous in terms of applications of photovoltaic cells.

並列關鍵字

first-principle ； silicon carbide ； Photoluminescence ； Bismuth ferrite ； leakage current

參考文獻

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