Review of encapsulation materials for AlGaN-based deep-ultraviolet light-emitting diodes

This paper reviews and introduces the techniques for boosting the light-extraction efficiency（LEE） of AlGaNbased deep-ultraviolet（DUV: λ < 300 nm） light-emitting diodes（LEDs） on the basis of the discussion of their molecular structures and optical characteristics, focusing on organoencapsulation materials. Comparisons of various fluororesins, silicone resin, and nonorgano materials are described. The only usable organomaterial for encapsulating DUV-LEDs is currently considered to be polymerized perfluoro（4-vinyloxy-1-butene）(p-BVE)terminated with a —CF;end group. By forming hemispherical lenses on DUV-LED dies using p-BVE having a —CF;end group with a refractive index of about 1.35, the LEE was improved by 1.5-fold, demonstrating a cost-feasible packaging technique.