## 4 Conclusions  
We have found that an AlN-DPC LF featuring encapsulation with durable silicone between the surface of an AlGaN-based UVB-LED chip and a quartz glass cover can enhance the LEE relative to that of the conventional packaging lacking the encapsulating silicone. The maximum enhancement in the LOP was 13.8% for the packaging type S1, in which the encapsulated silicone was positioned above the surface of the UVB-LED chip, but without a gap between the silicone and the quartz glass cover. In another packaging type (S2) in which the encapsulated silicone fully filled the cavity of the AlN-DPC LF that included an attached quartz glass as cover, the improvement in the LOP was 11.7%. The enhancement in the LOP was only 3.2% in the packaging type S3, in which a gap existed between the surface of the UVB-LED chip and the cover. Reliability tests performed over a period of 3500 h at a value of \(l_{\rm f}\) of 100 mA revealed that the LOPs of these three proposed packaging types decreased to 45.3, 48.6, and 50.3%, of their initial values, respectively; cracks had appeared in the encapsulated silicone after operation over an aging time of 1500 h and were evident in photographs taken after aging for 3500 h. Nevertheless, the different rates of degradation were not obviously correlated with the phenomena of cracks appearing in the encapsulated silicone during such long-term operation. From an investigation of the degradation of the LOPs, we suggest that, if silicone is used to encapsulate the cavity of the LF when packaging UVB-LEDs, the hermetic cover should be removed from the proposed package structure to avoid cracks occurring in the encapsulated silicone. Moreover, excluding any influences of degradation processes in UVB-LED chips, we suggest that the main mechanism responsible for the slow rates of degradation of the LOPs in these proposed UVB-LED packaging structures during longer periods of operation, after cracks had appeared in the encapsulated silicone, involves the silicone being further deteriorated by the UVB irradiation.  
Conceptualization, M.-J.L. and R.-M.L.; methodology, M.-J.L., T.-Y.L. and R.-S.L.; formal analysis, M.-J.L. and T.-Y.L.; investigation, M.-J.L., T.-Y.L. and R.-M.L.; data curation, M.-J.L., [PERSON]-B.W. and R.-S.L.; writing--original draft preparation, M.-J.L.; writing--review and editing, M.-J.L., R.-M.L., Y.-T.C., W.-H.S., X.Z. and L.-C.C.; visualization, [PERSON]-J.L., [PERSON]-Y.L. and R.-[PERSON]; supervision, M.-J.L. and R.-[PERSON]; project administration, M.-J.L., S.-M.H. and R.-M.L.; funding acquisition, S.-M.H. and R.-M.L. All authors have read and agreed to the published version of the manuscript.  
Figure 6: Time-dependence of the voltages measured at 100 mA during aging tests of samples S1–S4.  
**Funding:** This study was supported financially by the Ministry of Science and Technology (MOST) of Taiwan (contract no. MOST 109-2221-E-182-060) and Chang Gung Memorial Hospital BMRP 591.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Data is contained within the article.  
**Acknowledgments:** We thank [PERSON] for helpful discussions.  
**Conflicts of Interest:** The authors declare no conflict of interest.