Study of Optoelectronic Properties of Nano Structure InGaN/GaN Light Emitting Diodes

在奈米製程技術的進步發展下，有許多新奇的發光二極體結構被提出並表現出較好的元件特性，例如：奈米柱、奈米桿以及光子晶體元件等等。為了分析這些特殊的結構，我們利用了原子價力場模型與一致性的帕松、飄移擴散以及薛丁格方程式去設計、分析不同奈米結構下的氮化銦鎵/氮化鎵量子井發光二極體。首先，我們計算並描述了光譜能量藍移與應力釋放在不同尺寸的多重量子井奈米柱下的關係。並且，我們也研究了不同深度的蝕刻奈米洞陣列之氮化銦鎵/氮化鎵量子井發光二極體，而當奈米洞相當接近或穿透過量子井區域的時候，應力釋放效應與表面狀態效應對元件發光性質的影響被我們所分析。我們相信應力的釋放與奈米結構維度的尺寸將主要的影響其發光二極體的發光頻譜。在本篇論文中，我們將非常詳細地討論這些訊息。而應力鬆弛、壓電效應、表面狀態效應以及非輻射性複合機制等等在發光二極體中的作用都將被本篇論文所包含。我們的結果對於分析這類發光二極體之奈米結構的元件性質而言，可以提供許多有用的資訊。In the advance of nano technologies, many novel LED structures such as nanocolumn, nanorod, and photonic devices have been proposed to show better device performance. In order to analyze these structures, we have applied the valence force field model and self-consistent Poisson, drift-diffusion, and Schrodinger to analyze the InGaN/GaN quantum well LEDs with different nano structures. We first describe the correlation between the energy blue shifts and the strain relaxation of multiple quantum wells embedded in nanorods with different averaged sizes. We also studied the emission properties of InGaN/GaN quantum well light emitting diodes when the etching depths of nanohole arrays are close to or penetrate the quantum well structures. The effects of strain relaxation and surface states are analyzed, which could possibly influence the diode emission properties. Our results suggest that the effects of strain relaxation and sizes of nano structure dimensions strongly influence the emission properties of the nanorod LEDs. In this thesis, we will discuss these information in great detail. The roles of strain relaxation, piezoelectric effect, surface states, and non-radiative recombination mechanism will all be included in this thesis. Our calculation results can provide useful information in analyzing emission properties of these imilar nano structure LEDs.口試委員會審查表. . . . . . . . . . . . . . . . . . . . . . . . . i謝. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii文摘要. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv文摘要. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v錄. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii目錄. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . x目錄. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvi Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1 Prologue . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 III-V Nitride Compound Semiconductors . . . . . . . . 1.3 Quantum Confined Effect . . . . . . . . . . . . . . . . 4.4 Characteristics of the InGaN/GaN QuantumWell Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4.1 Defect Density and High P-type Doping in In-aN and GaN Materials . . . . . . . . . . . . . 7.4.2 Spontaneous Polarization and Strain-induced Piezoelectricolarization Effects . . . . . . . . . . . 9.4.3 Quantum Confined-Stark Effect . . . . . . . . . 14.4.4 Spontaneous Emission . . . . . . . . . . . . . . 16.5 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 17 Formalism . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.1 Electrical Properties of InGaN/GaN LEDs . . . . . . . 19.1.1 Valence Force Field (VFF) Model . . . . . . . . 19.1.2 The Total Polarization Charge Model . . . . . . 21.1.3 Self-Consistent Model . . . . . . . . . . . . . . 23.1.4 Fermi Distribution . . . . . . . . . . . . . . . . 29.2 Optical Properties of InGaN/GaN LEDs . . . . . . . . 32.2.1 Carrier Recombination Theory . . . . . . . . . . 32.2.2 Formula of Spontaneous Emission Rate . . . . . 37 Size Dependence of Strain Relaxation and Optical Propertiesrom InGaN/GaN Nanorod LEDs . . . . . . . . . . . . . . . 39.1 The Device Structures . . . . . . . . . . . . . . . . . . 41.2 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . 43.3 Summary . . . . . . . . . . . . . . . . . . . . . . . . . 56 Etching Depth Dependence of Emission Properties from Nanoholetructures . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58.1 The Device Structures . . . . . . . . . . . . . . . . . . 60.2 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . 61.3 Summary . . . . . . . . . . . . . . . . . . . . . . . . . 71 Conclusion and Future Work . . . . . . . . . . . . . . . . . . 73eference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7