具原子層沉積鈍化之紫外光微型發光二極體的光學特性分析與黃光能帶探討

Abstract

本研究所使用之外購之商用磊晶片，為紫外波段的 InGaN/AlGaN 結構。我們設計並製作了一系列方形微米級發光二極體（Micro-LED），其發光區域邊長分別為 2 µm、5 µm、10 µm、15 µm、20 µm、25 µm、50 µm、75 µm 與 100 µm。整體實驗流程涵蓋光罩設計、元件製程、電性量測及光學量測。 在結構設計方面，我們於 p 型電極與 p-GaN 之間引入氧化銦錫（ITO）透明導電層，以改善電流分布並降低金屬遮蔽造成的光取出效率損失。在乾蝕刻（ICP-RIE）後、氧化層沉積之前，我們於中央研究院進行原子層沉積（ALD）製程，以鈍化ICP 蝕刻引起的側壁缺陷，使側壁更加平整，同時降低側壁表面非輻射複合並提升外部量子效率（EQE）。此外，側壁缺陷的減少也能有效降低元件漏電流（leakage current），改善 Micro-LED 的電光表現。 本研究亦觀察到 InGaN/AlGaN UV Micro-LED 在 460–650 nm 波段產生的 Yellow band（YL band）缺陷發光。YL band 的存在會在光譜中引入額外的長波段發光組成，造成紫外光與缺陷光的混合，進而高估傳統量測下的 UV 輸出與 EQE。因此，本研究針對各尺寸元件進行 UV 與 Yellow band 分量分離分析，以獲得更準確的紫外光外部量子效率。此外，YL band 與側壁缺陷高度相關，其強度在小尺寸元件中更為顯著，顯示元件微縮後側壁佔比增加，進一步強化了缺陷相關的非輻射與深能階輻射復合行為。

This study utilizes commercially purchased InGaN/AlGaN ultraviolet epitaxial wafers provided by Epistar to fabricate a series of square micro–light-emitting diodes (Micro-LEDs) with mesa sizes of 2, 5, 10, 15, 20, 25, 50, 75, and 100 µm. The overall workflow includes photomask design, device fabrication, electrical characterization, and optical measurements. In the device structure, a transparent indium tin oxide (ITO) conductive layer is inserted between the p-type metal and p-GaN to improve current spreading and reduce metal-induced optical blocking, thereby enhancing light extraction. After the dry etching (ICP-RIE) process and prior to dielectric deposition, atomic layer deposition (ALD) was performed at Academia Sinica to passivate the sidewalls. This step effectively repairs plasma-induced sidewall damage, smooths the etched surfaces, suppresses non-radiative recombination at the sidewalls, and improves the external quantum efficiency (EQE). The reduction of sidewall defects also lowers the leakage current, further enhancing the electro-optical performance of the Micro-LEDs. Additionally, this study observes defect-related yellow-band (YL band) emission in the 460–650 nm wavelength range. The presence of the YL band introduces long-wavelength luminescence that mixes with the UV emission, leading to an overestimation of the measured UV output and EQE under conventional characterization. Since the YL band is strongly associated with sidewall-related deep-level defects, its impact becomes more pronounced in smaller devices with a higher perimeter-to-area ratio. To address this issue, spectral decomposition was conducted to separate the UV and yellow-band components, enabling a more accurate evaluation of the true UV external quantum efficiency and providing deeper insights into defect-induced emission in miniaturized Micro-LEDs.