Appl. Sci. 2021, 11, 9278. https://doi.org/10.3390/app11199278 www.mdpi.com/journal/applsci Article Observation of Highly Durable Silicone Resin for Encapsulating AlGaN‐Based UVB Light‐Emitting Diodes Mu‐Jen Lai 1 , Rui‐Sen Liu 1 , Tsung‐Yen Liu 2 , Shih‐Ming Huang 3 , Ray‐Ming Lin 2,4, *, Yi‐Tsung Chang 5 , Jian‐Bin Wu 5 , Wen‐Hong Sun 6 , Xiong Zhang 7 , and Lung‐Chien Chen 8, * 1 Jiangxi Litkconn Academy of Optical Research Co., Ltd, Jiangxi, Longnan City 341700, China; 15007070418@139.com (M.‐J.L.); asen2007@126.com (R.‐S.L.) 2 Department of Electronic Engineering and Institute of Electronics Engineering, Chang Gung University, Taoyuan 33302, Taiwan; vicliu7843@gmail.com 3 Department of Radiation Oncology, Chang Gung Memorial Hospital, Keelung 20401, Taiwan; skiwalkergg@gmail.com 4 Department of Radiation Oncology, Chang Gung Memorial Hospital, Linkou 33305, Taiwan 5 Department of Physics, School of Science, Jimei University, Xiamen 361021, China; oliver_ytchang@jmu.edu.cn (Y.‐T.C.); ayst1102@163.com (J.‐B.W.) 6 School of Physical Science and Technology, Guangxi University, Guangxi, Nanning 530004, China; youzi7002@gxu.edu.cn 7 Advanced Photonics Center, School of Electronic Science and Engineering, Southeast University, Nanjing 210096, China; esezx@seu.edu.cn 8 Department of Electro‐Optical Engineering, National Taipei University of Technology, Taipei 10608, Taiwan * Correspondence: rmlin@mail.cgu.edu.tw (R.‐M.L.); ocean@ntut.edu.tw (L.‐C.C.) Abstract: In this paper, we report an AlN‐based ceramic lead frame (LF) with encapsulating silicone between the surface of an AlGaN‐based ultraviolet‐B light‐emitting diode (UVB‐LED) chip and a quartz glass cover; the light output power (LOP) of this structure was 13.8% greater than that of the corresponding packaging structure without encapsulating silicone. Another packaging structure in which the silicone fully filled the cavity of the AlN‐based ceramic LF included covering with quartz glass; in this case, the enhancement of the LOP was 11.7%. Reliability tests performed over a period of 3500 h at a forward current (If) of 100 mA revealed that the LOPs of these two silicone‐containing packaging types decreased to 45.3 and 48.6%, respectively, of their initial values. The different degradation rates of these UVB‐LEDs were not, however, correlated with the appearance of cracks in the encapsulating silicone during long‐term operation. Excluding any possible mechanisms responsible for degradation within the UVB‐LED chips, we suggest that the hermetic cover should be removed to avoid the appearance of cracks. Moreover, the main mechanism responsible for the slow degradation rates of LOPs in these proposed packaging structures involves the encapsulated silicone, after cracks have appeared, undergoing further deterioration by the UVB irradiation. Keywords: AlGaN; ultraviolet; light emitting diodes; degradation; package; silicone; encapsulation 1. Introduction III‐Nitride‐based deep‐ultraviolet (DUV) light‐emitting diodes (LEDs) have a wide range of applications. For example, the emission wavelength of AlGaN‐based LEDs can be tuned by alloying GaN with AlN to cover almost the entire ultraviolet (UV) spectral range (200–365 nm), making them perfectly suited to applications in biological, environmental, industrial, and medical fields [1,2]. Furthermore, AlGaN‐based ultraviolet‐B LEDs (UVB‐LEDs) have been attracting great attention since the implementation of the Minamata Convention on Mercury. There is much potential for such LEDs to be used in medical (e.g., cancer immunotherapy; treatment of psoriasis, vitiligo, and pemphigus vulgaris) and agricultural (e.g., plant growth under UVB lighting; Citation: Lai, M.‐J.; Liu, R.‐S.; Liu, T.‐Y.; Huang, S.‐M.; Lin, R.‐M.; Chang, Y.‐T.; Wu, J.‐B.; Sun, W.‐H.; Zhang, X.; Chen, L.‐C. Observation of Highly Durable Silicone Resin for Encapsulating AlGaN‐Based UVB Light‐Emitting Diodes. Appl. Sci. 2021, 11, 9278. https://doi.org/ 10.3390/app11199278 Academic Editor: Giorgio Biasiol Received: 7 September 2021 Accepted: 4 October 2021 Published: 6 October 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses /by/4.0/).