劉致為Liu, Chee-Wee臺灣大學:電子工程學研究所陳志遠Chen, Chih-YuanChih-YuanChen2010-07-142018-07-102010-07-142018-07-102009U0001-2107200914264000http://ntur.lib.ntu.edu.tw//handle/246246/189209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。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.n 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.摘要 IIIbstract IVist of Figures VIIhapter 1 Introduction 1.1 Motivation 1.2 Organization 3.3 References 4hapter 2 Theoretical Calculation for Optical Gain of Relaxed and Strained Germanium 6.1 Introduction 6.2 Optical Gain Model 7.2.1 Indirect Optical Gain 7.2.2 Direct Optical Gain 12.3 The Simulation Result of Optical Gain for Ge 13.4 Strain Induced Optical Gain Enhancement 17.4.1 Biaxial Strain Effect on Germanium Band Structure 17.4.2 The Simulation Result of Optical Gain for Strained Ge 18.5 Summary 22.6 References 23hapter 3 Electronic and Optical Probability of Graphene and Graphene Nano-Ribons 25.1 Introduction 25.2 Electronic and Optical Properties of Graphene 26.2.1 Band Structure of Graphene 27.2.2 Optical Properties of Graphene 30.3 Electronic and Optical Property of Graphene Nano-Ribbons 33.3.1 Band Structure of Graphene Nano-Ribbons 33.3.2 Optical Probabilities of Graphene Nano-Ribon (GNR) 38.4 Summary 42.5 References 42hapter 4 Edge State and Orientation Effect of Graphene Nano-Ribbons 44.1 Introduction 44.2 Armchair and Zigzag Graphene Nano-Ribbons 44.3 Orientation Effect of Graphene Nano-Ribbons 47.3.1 Orientation Effect on Band Structures and Edge States 49.3.2 The Orientation Effect on Band Gap 52.4 Summary 56.5 Reference 56hapter5 Conclusion 58.1 Summary 58.2 Future Work 59.3 Reference 602719243 bytesapplication/pdfen-US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 gainGermanium lasersindirect band gaptensile straingraphene nano ribbontight bindingedge statethesishttp://ntur.lib.ntu.edu.tw/bitstream/246246/189209/1/ntu-98-R96943045-1.pdf