本論文主要為金屬共振腔結構之研究且利用模擬軟體來改善且提升光學特性並藉以製作氮化鎵藍綠光垂直式面射型雷射元件。包括光學侷限因子、光學侷限品質因子、材料光增益頻譜和效率等項目，皆會列入提升光學性質的考量。
於分析室溫下金屬共振腔光譜的研究中，我們發現到此種結構能有效的提供良好的光學侷限環境。此意味著利用金屬共振腔結構的方式來製作氮化鎵藍綠光垂直式面射型雷射元件是具有相當可觀的發展空間。由於取得的共振腔為多重模態之光譜，常見的Hakki-Paoli method可將透過微光致螢光光譜儀量測而來的資料處理後代入計算金屬共振腔的在閾值前半導體增益值進而分析尺寸效應對金屬共振腔結構的影響。當金屬共振腔直徑尺寸為5微米時，我們可發現到半導體增益極大值因微型共振腔效應而能有效地從10^-4 cm^-1 提升一個級距至 10^-3 cm^-1。因此尺寸縮減實則有益於提升氮化鎵金屬共振腔的光學特性。然而元件尺寸的縮減也意謂製程困難度的提升。
基於垂直式面射型雷射有較小的增益層體積且為達到最大的模增益，將光場強度盡可能地集中於量子井區域顯得相形重要許多。我們透過COMSOL軟體模擬導波管的光學性質來找出符合元件尺寸需求的最佳化之光學侷限特性，包括光學侷限因子(Γ)、光學共振腔侷限品質因子(Qcavity)以及相對應的光場圖形。純粹以光學觀點而言，我們在基模的模擬結果下發現到Γ和Qcavity對於共振腔直徑的尺寸的影響並不顯著。然而在元件深度增加至為2.5微米時，對經由模擬軟體計算而得之Qcavity的整體而言皆已提升至99%左右，其表示光學侷限效果已達飽和。反觀Γ，其整體值大多約為19.3%其並無顯著有效地提升。因此我們可以推斷Qcavity和共振腔深度息息相關，藉由增加共振腔深度或是n-GaN厚度皆能有效的提升Qcavity並得到良好的光學侷限效果。然而欲增加共振腔深度勢必得進行深蝕刻製程，意即透過長時間反應式離子蝕刻程序，此將造成結構側壁損壞進而影響光學效率。對於Γ而言，則與主動區位置有密切關連。因此，為提升光學侷限能力，我們以折射率侷限性質為基礎概念進行結構的調整，將p型氮化鎵層厚度由600奈米減少至150奈米並把主動層厚度由240奈米增加至450奈米，設計出新結構且找到最佳的光學侷限效果。在新改良結構的基模模擬結果中發現，其共振腔深度僅為1.5微米時，相對應的Γ整體皆大幅提升至31%，而Qcavity整體數值更已達99%，表示光學侷限效果已達飽和狀態。所以，藉由模擬結果取得最佳的共振腔的光學特性，用此調整共振腔主動層厚度的位置並重新評估且設計磊晶參數來避免不利的深蝕刻製程，對於元件特性的改良和製作實為重要顯著。
最後，利用改善過後的新磊晶結構來製作以金屬共振腔為概念的光激發以及電激發的藍綠光氮化鎵垂直式面射型雷射元件，我們也成功的在低溫15K製作出光激發藍綠光氮化鎵雷射垂直式面射型元件並且確認了電元件製作的可行性。在共振腔尺寸為深度1.5微米、直徑為15微米時，透過變功率式脈衝雷射的光致螢光光譜的量測，其結果可透過顯著的slope efficiency變化來估計在閾值80 MW/cm^2下，對應的半導體增益極大值為1.126 × 10^3 cm^−1且元件已達雷射操作狀態而對應的波長約為521 奈米 (2.38 eV)，即為綠光波段，且其增益頻譜對於雷射元件的發光效率也較為理想。反觀直徑為20微米時，其半導體增益極大值為1.007 × 10^3 cm^−1，表示雖已達lasing狀態，但其較寬的增益頻譜會造成能量的損耗，亦對雷射元件的發光效率較不理想。因此，本研究成果明確地顯示出以金屬共振腔為概念於製作垂直式面射型雷射元件的過程中，實則扮演重要角色且有能所突破。

The main purpose of this dissertation is to investigate metal-assisted structure and develop the bule-green GaN-based vertical surface emitting lasers (VCSELs) by the simulations and some approaches to improve the performances. The performance improvement will be considered in respect of optical properties including optical confinement factor and optical quality confinement factor, material gain spectra, and efficiency.
In respect of research on the metallic-coated cavity under optical pumping conditions at room temperature, we found the structures could efficiently provide good optical confinement. It implied the metal-cavity microlasers provide a great potential choice for constructing GaN-based VCSELs. Due to multiple cavity modes in the structure, the optical gain could be calculated from the micro- photoluminescence (μ-PL) spectrum below the threshold condition by the Hakki-Paoli method. Furthermore, the optical gain along with the size effect of metallic-coated structure was hence analyzed. When diameter of metal-cavity is 5 μm, αMax is enhanced by one order from 10^-4 cm^-1 to 10^-3 cm^-1 due to the microcavity. The effect of size shrinkage provided good performance of metallic GaN-based cavity; nevertheless it increased the difficulty of fabricating process.
On account of the small gain volume of VCSELs, it was essential to confine the optical-field intensity as much as possible in the quantum wells in order to achieve maximum modal gain. The optical confinement factor was crucial for the resonant cavity to decide the capability of optical property. Simulation of wave guiding for optimum optical confinement told us the required scales of device to attain the threshold condition. The COMSOL software was chosen for calculating the optical properties including optical confinement factor (Γ), optical quality factor of cavity (Qcavity) and correspondent patterns of electric fields. For fundamental mode, the diameter of the resonant cavity had little influence on Γ and Qcavity in the viewpoint of optics. As for the depth of metal-cavity at 2.5 μm, all values of Qcavity were approximately 99%, which indicated the optical confinement capability was saturated. However, all values of Γ were around 19.3% but not been well improved. Qcavity depended on the depth of the resonant cavity and could be improved by increase the depth of the resonant cavity and the thickness of n-GaN. However, deep etching (long term ICP etching) was necessary to obtain the high depth pillar structures and could lead to damages on the sidewall of pillars. Besides, Γ depended on the position of active region layer. In behalf of improving the optical properties of resonant cavity, the new design structure could be tuned by reducing the thickness of p-GaN from 600 nm to 150 nm and increasing the thickness of active region from 240 nm to 450 nm. As for the depth of new design metal-cavity at 1.5 μm under fundamental mode, all values of Γ were well improved to around 31% and all Qcavity were approximately 99%, which indicated the optical confinement capability was saturated. It was essential to optimize the best optical properties of resonant cavity by tuning the position of active region and epitaxial parameters to avoid the harmful deep-etching process.
Finally, Demonstrations of optical pumping laser of our device indicated that fabricating metal-cavity blue-green GaN-based VCSELs is feasible. We successfully demonstrated the metal-cavity GaN-based cavity under optical pumping conditions at 15 K when the diameter and the depth of metal-cavity were 15 μm and 1.5 μm, respectively. The peak material gain of about 1.126 × 10^3 cm^−1 was obtained at the threshold condition about 80 MW/cm^2. Above the threshold condition, only one lasing mode dominated and the obvious change of slope efficiency was found. The peak gain of the lasing mode was at about 521 nm (2.38 eV). The sample with diameter of 20 μm had the peak material gain at 1.007 × 10^3 cm^−1. However, the broadening gain spectrum might reduce the performance of laser devices. This work unequivocally indicates that the metal-assisted structure used on the VCSELs was an important role in lasing action. The results presented here represent a breakthrough in the metal-coated GaN-based VCSELs.

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