泛涵密度理論於硫化氫在Group IV (Si, Ge/Si, Ge) 半導體表面吸附與反應之研究

Density Functional Theory Study of H2S Adsorption and Reaction on Group IV (Si, Ge/Si, Ge) Semiconductor Surfaces

鄧宗凡(Tsung-Fan Teng)

指導教授 ： 洪偉修

國立臺灣師範大學/理學院/化學系/博士(2012年)

摘要

本文利用泛函密度理論(DFT)探討硫化氫(H2S)在Si(100)-c(4x2)表面, Ge/Si (100)-c(4x2)與Ge(100)-c(4x2)表面上的吸附和反應。在這次研究中，我們發現了四種最穩定產物，其中一個是從來未在文獻中討論過的；這四種穩定產物都是從硫化氫分子吸附經由二次的氫解離，到硫原子跨橋鍵結的過程。另外，經由DOS分析發現Si (100)表面, Ge/Si (100)表面和Ge (100)表面擁有相似的特徵，其中都以c (4×2)為最穩定的表面。
在三者表面上，我們利用理論計算探討表面特性，包括鍵角、鍵能及鍵長；當硫化氫吸附上表面，我們也利用計算提供了中間物和產物的吸附能、鍵角、鍵長、振動波長、結合能以提供後續實驗化學家參考。
根據理論計算數據，我們也畫出反應能量圖，藉由此圖我們可清楚知道反應路徑、反應機構及能量的變化。在四個穩定產物中，其中兩個產物比較取決於動力學下的產物：另外中兩個產物比較取決於熱力學下的產物。主要原因在於速率決定步驟時的活化能以及產物的相對能量。根據反應能量圖，我們也發覺有些反應活化能較小，也利用了EDD(electron density difference) 去探討電子密度的分布來找到合理的解釋。
再者由於電子產品的不斷創新，本實驗也提供了不同材料表面的探討，原來由鍺來替換矽材料，是希望藉由鍺的電子高移動速率，達到較高品質的電子產品，但鍺表面的易氧化帶來負面效果，所以探討了在矽表面濺鍍一層鍺的表面特性。

關鍵字

泛函密度理論 ； 硫化氫 ； 矽(100) ； 鍺/矽(100) ； 鍺(100) ； X光光電子光譜 ； 電子密度差分析 ； 電子狀態分析 ； 矽

並列摘要

The adsorption and reaction of H2S on semiconductor surfaces (Si(100), Ge/Si(100) and Ge(100)) were investigated by using density functional theory (DFT). In this thesis, we found four stable products and they came from four steps including first dehydrogenation, second dehydrogenation, hydrogen migration and sulfur bridged ring formation. In addition, FSIII is rare reported in previous studies. The c(4x2) reconstruction surface is the most stable surface on Si(100), Ge/Si(100) and Ge(100).
We summarized the bond lengths, the relative energies, the adsorption energies binding energies and vibration frequencies on Si(100), Ge/Si(100) and Ge(100) three surfaces.
We propose four reaction paths for the decomposition of adsorbed H2S; the corresponding structural conformations of H2S, HS and S species are presented. Two pathways are kinetic control pathways according to the low energy barriers of the rate determining steps. The other pathways are thermodynamic control pathways because of the stable final products. The electron of state (DOS) and the electron density difference (EDD) were utilized to illustrate the interaction between S-containing species and surface Ge or Si atoms. In addition, the electron density difference (EDD) can help us explain the low energy barrier in first dehydrogenation and IR vibration frequencies have big red shifts in S-H stretching adsorption of H2Sad.
Furthermore, the XPS and IR calculated data can offer information for experimental peak assignments. Because the sizes of microelectronic devices have gotten as small as possible, the passivation layers are important issue for semiconductor surfaces. The Ge has high mobility and the Si has stable silicon oxide interface, so the Ge/Si surface may be another worth studying surface in semiconductor field.
Key words: silicon, H2S, X-ray photoelectron spectra, density functional theory, electron density difference (EDD), electron of state (DOS).

並列關鍵字

DFT ； H2S ； Si(100) ； Ge/Si(100) ； Ge(100) ； x-ray photoelectron spectra ； electron density difference (EDD) ； electron of state (DOS) ； silicon

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