室溫下於金屬鍍膜之氮化鎵奈米共振腔之雷射特性

Abstract

本論文中，我們展現了在室溫下從金屬鍍膜之氮化鎵奈米共振腔觀察到雷射訊號的可能性。 首先我們利用電子束微影在未參雜的氮化鎵薄膜上定義出條狀的結構，並在此結構上方覆蓋上一層介電質材料和鋁金屬。由微光致螢光量測系統所得的實驗結果，我們觀察到了單一模態的雷射訊號，其波長約略三百七十奈米，並由實驗結果反推出其品質因數大約為150。除此之外，藉由模擬的方式來分析此實驗結果，我們也證明了鍍在奈米結構上的鋁金屬大大提升了此結構對於光場的局限能力。我們相信此雷射模態是由波導的模態和表面電漿的模態所混合而成的。 第二個部分，我們驗證了室溫下在金屬鍍膜之環狀奈米結構中雷射的可能性。我們利用迴音壁模態和表面電漿模態做一結合，達到在奈米結構中觀察到雷射訊號的目標。最小的環形共振腔其直徑為三微米，環的寬度約為310奈米。和前一章之條狀結構之元件特性做比較，我們可以得到更高的品質因子及更低的閥值能量密度，且環形的寬度更可以達到次波長的領域，並且大幅度的縮小整個元件大小。可見環形結構一如預期可利用回音壁模態來大幅提升奈米級半導體雷射的元件表現。

In this thesis, we demonstrated metal-coated GaN nanocavity laser operable at room temperature by optical pumping. We first utilized fabrication process to define the nanostripe pattern on undoped GaN layer grown on a sapphire substrate, with a thin dielectric layer and aluminum layer coated on it. From micro-photoluminescence measurement result, we observed a single mode lasing at room temperature with lasing wavelength around 370nm and the quality factor was about 150. Moreover, by simulation analysis, we proved the aluminum layer coated on the nanostripe strongly enhance the optical confinement of this nanocavity. We believed that this lasing mode was a combination of waveguide mode and surface plasmon mode. Second, we demonstrated lasing in metal-coated GaN nanoring at room temperature. We utilize whispering-gallery-mode with surface plasmon mode to achieve lasing in a nanoring cavity. The diameter of the smallest ring is 3μm, and the width of the nanoring is about 310nm. Compare with the device performance of metal-coated GaN nanostripe, we got a higher quality factor and lower threshold power density. The width of the nanoring could shrink to subwavelength scale and the size of the device can be reduced significantly. This result proved our assumption that whispering-gallery mode would improve the performance of nanolaser.