## 2 Materials and Methods  
Figure 1 provides a schematic representation of the epitaxial structure of the AlGaN-based NB-UVB LED, which was obtained using low-pressure metal-organic chemical vapor deposition (LP-MOCVD). Trimethylaluminum (TMA), trimethylgallium (TMG), bis(cyclopentadienyl)magnesium (Cp\({}_{2}\)Mg), ammonia (NH\({}_{3}\)), and silane (diluted with H\({}_{2}\) to a concentration of 30 ppm) were used as Al, Ga, Mg, N, and Si sources, respectively. The TMA, TMG, and Cp\({}_{2}\)Mg precursors, exhibited the typical purity grade of \(\geq\)99.9999%, were obtained from Nata Optoelectronic Material (China). Additionally, the purity grade of NH\({}_{3}\) was over 99.9999% through a purification process. First, a 2.2 um-thick AlN buffer layer was grown on a 2 inch (0001)-oriented sapphire substrate. Next, a strain-relieving interlayer, consisting of 30 periods of an AlN/AlGaN superlattice with an equivalent Al composition of 0.72, was grown on the AlN buffer layer. A 1.5 um-thick layer of undoped Al\({}_{0.6}\)Ga\({}_{0.4}\)N was then grown on the superlattice interlayer, followed by a 2 um-thick Si-doped n-Al\({}_{0.5}\)Ga\({}_{0.5}\)N layer as the n-contact layer. The active region of multiple quantum wells (MQWs) included five pairs of 2.2 nm-thick Al\({}_{0.35}\)Ga\({}_{0.65}\)N quantum wells (QWs) and 10 nm-thick Al\({}_{0.45}\)Ga\({}_{0.55}\)N quantum barriers (QBs), followed by a twofold Mg-doped p-Al\({}_{0.55}\)Ga\({}_{0.45}\)N (10 nm)/Mg-doped p-Al\({}_{0.4}\)Ga\({}_{0.6}\)N (2 nm) structure as the electron blocking layer (EBL). Subsequently, a 50 nm-thick Mg-doped p-AlGaN layer, with the Al content grading from 30% to 0%, was grown on the EBL. Finally, a 20 nm-thick Mg-doped p-GaN layer was deposited, serving as the p-contact layer. After growing the epitaxial layers, the sample was annealed in situ under a N\({}_{2}\) ambient to activate the Mg dopants at 700 \({}^{\circ}\)C for 15 min. UVB-LED chips were fabricated using standard flip-chip processing technologies. All the metal sources exhibited the typical purity grade of \(\geq\)99.999%. Mesa structures were defined using an inductively coupled plasma (ICP) dry etching system to expose the n-Al\({}_{0.5}\)Ga\({}_{0.5}\)N layer surface down to an etching depth of 0.5 \(\upmu\)m. Next, n-contacts of Ti/Al/Ti/Au (100/200/30/100 nm) were deposited through electron-beam (EB) evaporation and subjected to rapid thermal annealing (RTA) at 980 \({}^{\circ}\)C for 60 s. To form a transparent p-contact, a 50 nm-thick layer of indium tin oxide (ITO) was sputtered on top of the p-GaN layer, and then the sample was annealed at 600 \({}^{\circ}\)C for 10 min. The UVB-LED chips were then fabricated by using EB evaporation to deposit Ti/Pt/Au (50/30/100 nm) on both the n-contacts of the metals and the ITO film. Moreover, a 1-\(\upmu\)m-thick passivation layer of SiO\({}_{2}\) was deposited. Finally, a 3 \(\upmu\)m-thick layer of AuSn alloy was deposited to form the bonding pads. The processed wafer was then lapped and scribed into dimensions of 550 \(\times\) 550 \(\upmu\)m\({}^{2}\). The prepared UVB-LED chips were separately flip-bonded onto four AlN-DPC LFs through soldering; a quartz glass covering served as an optical lens for each packaged sample. Structural diagrams of the four package types (S1-S4) are displayed in Figure 2. The yellow part is the DPC film with an Au coating over the surface; the blue part is the LED chip; the green part is the encapsulated silicone; the pink part is the quartz glass; and the black part is the AlN ceramic material. S1 is a packaging type in which the encapsulated silicone is positioned above the surface of the UVB-LED chip, but with a gap preserved between the silicone and the quartz glass cover. S2 denotes a packaging type featuring the encapsulated silicone above the surface of the UVB-LED chip, but without a gap between the silicone and the quartz glass cover. Notably, the cavities in the AlN-DPC LFs of samples S1 and S2 did not have any filling silicone.