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標題: | 氮化銦鎵自聚式量子點結構之機械與光電性質研究 Mechanical and Optoelectronic Properties of InGaN Self-Assembled Quantum Dots |
作者: | Wei-Yi Tsai 蔡緯毅 |
指導教授: | 郭茂坤 |
關鍵字: | 氮化銦鎵,量子點,線彈性壓電力學,濃度分佈,壓電常數,量子井,非局部彈性力學, InGaN,Quantum dots,Piezoelectricity,k.p Hamiltonian,Quantum well,Nonlocal Elasticity, |
出版年 : | 2010 |
學位: | 碩士 |
摘要: | 本文主要針對烏采(wurtzite)結構氮化銦鎵(InGaN)自聚式量子點結構之各種假設條件逐步探討機械與光電性質,內容分為四大主題: 銦濃度分佈對自聚式氮化銦鎵量子點之穿隧能量(transition energies)的影響、壓電常數對自聚式氮化銦鎵量子點之電子結構的影響、量子井結構對量子點結構之影響、非局部線性彈性力學理論對量子點機械與光電性質之影響。我們運用線性壓電力學與k•p理論輔以有限元素法進行量子點應變壓電場與特徵能量的模擬運算;數據顯示,對於電子之穿隧能量理論模擬,橢球之濃度分佈假設與均值分佈具有較相近行為表現,對電洞而言,則為線性與均值較為類似,此外,濃度分佈的差異並不會對庫倫交互作用造成顯著之影響,整體而言,銦濃度分佈在線性形式的假設下會有最大之穿隧能量,橢球假設則為最小。另一個研究結果則顯示,在不考慮壓電常數(e15)之情況下,其壓電勢能為624 mV,反之,若考量壓電常數(e15),其值將大幅提升至766 mV,因而忽略壓電常數時將高估量子點之穿隧能量。此外,隨著量子點高度提升,此兩種假設條件對於穿隧能量的影響差距將益發顯著,特別的是當改變量子點底部直徑時,其間之差距維持定值,因此在探討量子點電子結構時,此項參數有其考量之必要性。而量子點結構在加入量子井之後,不論是穿隧能量亦或是庫倫作用力均被大幅提升,相較於改變量子井與濕潤層間的距離(d),量子井厚度(t)與濃度(beta)的效應對於不同形狀量子點的QDQW結構之光學特性擁有顯著影響,相對而言,不論是量子井之厚度、濃度或是量子井與濕潤層間的距離,其所產生的擾動效應對於QDQW結構之庫倫作用力均無顯著的影響,因此擁有不同設計條件效應之量子井結構對於影響傳統量子點結構之光電性質扮演極為重要的角色。考慮非局部線性彈性力學理論時量子點承受應變程度較傳統線性彈性力學理論為弱,由於採用此理論明顯使應變降低,使得應變所引致之壓電場(piezoelectric potential)也大幅下降,應變與壓電場的變化也使電子與電洞的基態能量發生改變,因此穿遂能量也會變動。電子基態能階,隨量子點高度變大,而急遽下降,而隨著量子點結構底部直徑的變大,電子基態能階也隨之下降,特別的是;電洞的基態能階,隨量子點高度變大而上升,隨著量子點底部直徑的變大,也使電洞基態能階上升。因此,在模擬一般實驗常見之量子點結構機械與光電性質,均需引入非局部彈性力學。 In this work, we investigate the variation of electronic structures of self-assembled InGaN/GaN quantum dots (QDs) due to (a) indium distribution within QDs; (b) piezoelectric constant e15; (c) QD structures; and (d) nonlocal theory in strain. Strain and piezoelectric fields, single-particle state energies and wave functions of the QDs are all estimated by a commercial finite element package—COMSOL, with the aid of theory of piezoelectricity and a k•p Hamiltonian. Based on simulation results, electron (hole) energy for QDs with ellipsoid (linear) indium distribution has similar behavior to those with uniform indium distribution. On the other hand, the Coulomb interactions of these three indium distributions are not significantly different. We find also that, on optical properties of QDs, piezoelectric constant e15 cannot be neglected. Since piezoelectric potential will be underestimated by an amount of 142 mV (from 766 down to 624 mV) by neglecting e15, and hence leading to an overestimation in transition energy. Moreover, this discrepancy will increase with the size of QDs increase. In the third part of this thesis, we find that the transition energies of the QDs are able to be promoted about 53 meV by inserting QDs in between two quantum wells (QWs). And QWs play critical roles in changing the piezoelectric potential and the Coulomb interaction of QDs. In the fourth part, we find that, by introducing nonlocal theory in strain, the strain and piezoelectric potential decrease significantly. Consequently, the nonlocal elasticity theory has a great impact on the electron and hole ground-state energies. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/10599 |
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顯示於系所單位: | 應用力學研究所 |
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