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http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/25879
Title: | 鍺半導體之光學增益模型與單層石墨之光電特性 Theoretical Model for Optical Gain of Germanium & Electronic and Optical Properties of Graphene & Electronic and Optical Properties of Graphene |
Authors: | Chih-Yuan Chen 陳志遠 |
Advisor: | 劉致為(Chee-Wee Liu) |
Keyword: | 光學增益,鍺半導體雷射,非直接能,伸張應力,奈米石墨帶,緊束模型,邊緣電子模態, Optical gain,Germanium lasers,indirect band gap,tensile strain,graphene nano ribbon,tight binding,edge state, |
Publication Year : | 2009 |
Degree: | 碩士 |
Abstract: | 本論文包含兩個主題。在第一個主題中,我們推導了鍺半導體的光學增益模型並探討鍺半導體在雷射應用上的可能性。透過未伸展形變與伸展形變鍺半導體之光學增益模擬結果,我們發現鍺半導體中之光學增益確實可經由雙軸伸張應力而獲得提升。然而,過大的伸展應力將會使鍺半導體之光學增益頻譜紅移,並造成1550nm區域之光學增益減少。透過本模擬計算,最佳的形變條件是1.25%的伸張形變,其最低之臨界輸入載子密度為4.35x1019 cm-3。
在第二個主題中,我們探討了單層石墨與奈米石墨帶之電子與光學特性。我們利用最鄰近緊束模型(Nearest neighbor tight binding model)計算其能帶結構。並根據此能帶結構,搭配緊束哈密爾敦之梯度函數,得到其吸收光譜。此外,我們也探討了奈米石墨帶之位相效應的問題。隨著位相角度的增加,越來越強大的邊緣電子模態會縮小奈米石墨帶之能隙。我們的計算結果顯示:邊緣電子模態受位相變化的影響是非常敏銳的,即使只有6.6°的位相變化也會造成很強的邊緣電子模態。 There are two topics included in this thesis. In the first topic, we develop a theoretical model for optical gain of Germanium (Ge) to investigate the possibility for Ge to be applied into the laser devices. Optical gains of relaxed and tensile strained Ge are all simulated using many reasonable material parameters. Our simulation results show that the optical gain can be much enhanced by biaxial tensile strain, and making the laser application possible for Ge. However, excessively large tensile strain would also cause the red shift of gain spectrum and eliminate the gain at 1550nm. The optimum strain condition for Ge 1550nm laser is 1.25% tensile strain and the minimum threshold injected carrier density is 4.35x1019 cm-3. In the second topic, we discuss the electronic and optical properties of graphene and graphene nano ribbon (GNR). The nearest-neighbor tight binding approximation is used to calculate the band structures for the systems. Based on these band structures, the absorption spectra can be obtained with the k-space gradient of the tight-binding Hamiltonian. The issue of the orientation effect in GNR is also discussed. Due to the stronger and stronger edge state, the band gap of GNR shrinks at higher orientation angles. Our calculation result shows the subtle reaction of edge state to the changing of the orientation. Even an orientation as small as 6.6° can induce a very strong edge state. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/25879 |
Fulltext Rights: | 未授權 |
Appears in Collections: | 電子工程學研究所 |
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ntu-98-1.pdf Restricted Access | 2.66 MB | Adobe PDF |
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