室溫下金屬塗層氮化鎵之光柵結構之雷射特性

Abstract

本論文中，我們於室溫下金屬塗層氮化鎵之光柵結構中觀測到雷射訊號的表現，並展現金屬塗層在光柵結構中的重要性。 第一個主題部分，我們先利用有限元法近似解的模擬工具對光柵結構進行設計與優化，之後使用電子束微影技術在未參雜的氮化鎵材料上定義出光柵結構圖形，接著將氮化矽介電質材料與鋁金屬塗佈在此結構表層。在元件製作完成後，我們用掃描式電子顯微鏡去確認光柵結構元件的週期、寬度與深度是否與我們模擬所設計的結構尺寸相同。此後，由微光激發螢光量測系統對樣品進行量測，從實驗結果中我們觀察到了一波長約三百六十八奈米的單一模態能帶邊緣型雷射訊號，並概算出品質因數約為570。隨後，藉由有限元法近似解去模擬有無金屬塗層的氮化鎵光柵結構，我們證明了鋁金屬塗層確實大幅度提升了光柵結構對於光場的侷限能力。由實驗與模擬結果，我們相信此能帶邊緣型雷射模態是由於表面電漿的模態與部分的波導模態和所達成的。 第二個主題部分，我們選擇性改變光柵結構的等效折射率，更進一步設計出具有低閥值優點的缺陷模態雷射。我們改變光柵結構的其中一條狀結構寬度，並從有限元法近似解確認了缺陷模態的存在。從實驗結果中我們也觀察到了一波長約三百六十四奈米的缺陷型模態雷射訊號。和前一章之光柵結構之元件特性相比，缺陷模態光柵結構具有超低閥值能量密度的表現，並承諾了未來低耗能光電元件發展的可行性。

In this thesis, we observe the lasing action of metal-coated GaN grating structures at room temperature and show the importance of metal which is coated on the surface of grating structure. In the first part of this thesis, we use finite element method to design and optimize the grating structure. Then, we define the grating pattern on the undoped GaN by e-beam lithography. After that, we deposit the Si3N4 dielectric layer and coat the aluminum on it. Next, we use scanning electron microscope to check the period, width and height of grating structure. We observe a band edge lasing mode from the metal-coated GaN grating structure at 368nm by micro-photoluminescence system and estimate the quality factor of it which is about 570. We simulate the electric field of grating structure with and without metal and confirm that the metal-coated layer actually enhances the optical confinement of grating structure. From the experiment and simulation results, we believe that the band edge lasing mode is due to the surface plasmon polaritons and part of dielectric mode. In the second part of this thesis, we selectively change the effective refractive index of grating structure and further design the defect mode laser with ultra-low threshold. We change one stripe’s width of grating structure and confirm that the defect mode actually exists in it by finite element method. The defect modes lasing at 364nm is observed under room temperature condition. Compared to grating structure, the defect grating structure has ultra-low threshold power density which gives a promise to develop the photoelectric device with low energy consumption in the future.