AlGaN-based ultraviolet-C (UV-C) light-emitting diodes (LEDs) face challenges related to their extremely low external quantum efficiency, which is predominantly attributed to the remarkably inadequate transverse magnetic (TM) light extraction efficiency (LEE). In this study, we employ angle-resolved cathodoluminescence (ARCL) spectroscopy to assess the optical polarization of (0001)-oriented AlGaN multiple quantum well (MQW) structures in UV-C LEDs, in conjunction with a focused ion beam and scanning electron microscopy (FIB/SEM) system to etch samples with various inclination angles (θ) of sidewall. This technique effectively distinguishes the spatial distribution of TM- and transverse electric (TE)-polarized photons contributing to the luminescence of the MQW structure. CL spectroscopy confirms that UV-C LEDs with a θ of 35° exhibit the highest CL signal compared to samples with other θ. Furthermore, we establish a model using finite difference time domain (FDTD) simulation to validate the mechanism of the outcomes. The complementary contribution of TM and TE photons at different specific angles are distinguished by ARCL and confirmed by simulation. At angles near the sidewall, the CL is dominated by the TM photons, which mainly contribute to the increased LEE and the decreased degree of polarization (DOP) to make the spatial distribution of CL more uniform. Additionally, this method allows us to analyze the polarization of light without the need for polarizers, enabling the differentiation of TE and TM modes. This distinction provides flexibility for selecting different emission mode based on various application requirements. The presented approach not only opens up new opportunities for enhanced UV-C light extraction but also provides valuable insights for future endeavors in device fabrication and epitaxial film growth.

中文翻译：

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角度分辨阴极发光研究紫外-C AlGaN 多量子阱的光学偏振特性

基于 AlGaN 的紫外 C (UV-C) 发光二极管 (LED) 面临着极低的外部量子效率的挑战，这主要归因于横向磁 (TM) 光提取效率 (LEE) 明显不足。在这项研究中，我们采用角分辨阴极发光 (ARCL) 光谱，结合聚焦离子束和扫描电子显微镜，评估 UV-C LED 中 (0001) 取向 AlGaN 多量子阱 (MQW) 结构的光学偏振(FIB/SEM) 系统蚀刻具有不同侧壁倾斜角 (θ) 的样品。该技术有效地区分了对 MQW 结构发光有贡献的 TM 偏振和横向电 (TE) 偏振光子的空间分布。 CL 光谱证实，与具有其他 θ 的样品相比，θ 为 35° 的 UV-C LED 表现出最高的 CL 信号。此外，我们使用时域有限差分（FDTD）模拟建立模型来验证结果的机制。 ARCL 区分了 TM 和 TE 光子在不同特定角度的互补贡献，并通过模拟证实。在靠近侧壁的角度处，CL以TM光子为主，这主要有助于LEE的增加和偏振度（DOP）的降低，从而使CL的空间分布更加均匀。此外，这种方法使我们能够在不需要偏振器的情况下分析光的偏振，从而区分 TE 和 TM 模式。这种区别为根据各种应用要求选择不同的发射模式提供了灵活性。所提出的方法不仅为增强 UV-C 光提取开辟了新的机会，而且还为未来器件制造和外延膜生长的努力提供了宝贵的见解。