Photonics Research, Volume. 7, Issue 8, B55(2019)
Review of encapsulation materials for AlGaN-based deep-ultraviolet light-emitting diodes
Fig. 1. Cracks in silicone encapsulation of AlGaN-based (a) 270 nm, (b) 287 nm, and (c) 301 nm LEDs after the reliability tests. The time and the operation current during the reliability tests are indicated at the top of the photographs. The insets are magnified images of the cracks. [Figure 1(c) is taken from Ref. [27]. Copyright Japan Society of Applied Physics.]
Fig. 2. Absorption spectrum of silicone with side chains of methyl groups with the molecular structure shown as an inset. The weak absorption observed between approximately 250 and 280 nm is considered to be that of the polymerization initiator. (Reproduced from Ref. [27]; copyright Japan Society of Applied Physics.)
Fig. 3. (a) Transmittance spectra of p-BVEs with various end groups and PDD-co-TEF; (b) molecular structures of (left) p-BVEs with (─R) (
Fig. 4. Photographs of the damage to the electrodes after reliability tests using 265 nm LEDs. A similar phenomenon was observed for p-BVE with the ─COOH end group for a 285 nm LED after a reliability test for 804 h [25]. When the damage to the electrodes occurred, a significant increase in the leakage current occurred. (Taken from Ref. [27]; copyright Japan Society of Applied Physics.)
Fig. 5. Bubbles appearing after reliability tests for 32 and 105 h followed by heating up to 230°C for the p-BVE with ─COOH and
Fig. 6. Damage to the electrodes after reliability tests for 3137 and 832 h at a driving current of 200 mA for 262 nm LEDs wrapped with (a) p-BVE with the
Fig. 7. TPD-MS spectra for
Fig. 8. (a) Decomposition paths for p-BVE with ─COOH end group; (b) alignment of the end group on the electrode surface in the case of ─COOH. The neighboring ─COOH is one of the reasons for the early occurrence of electrode damage in the case of p-BVE with the ─COOH end group.
Fig. 9. (a) TPD-MS spectra of
Fig. 10. TPD-MS spectra for (a)
Fig. 11. (Upper) Path for the creation of voids in the case of PDD-co-TFE and (lower) structure after the void creation. The undetectable species due to the high vapor pressure are indicated by “*”.
Fig. 12. Light extraction enhancement ratio (
Fig. 13. (a) Photograph of the fabricated lens array on a
|
|
Get Citation
Copy Citation Text
Yosuke Nagasawa, Akira Hirano, "Review of encapsulation materials for AlGaN-based deep-ultraviolet light-emitting diodes," Photonics Res. 7, B55 (2019)
Special Issue: SEMICONDUCTOR UV PHOTONICS
Received: Jan. 22, 2019
Accepted: May. 2, 2019
Published Online: Jul. 29, 2019
The Author Email: Akira Hirano (hirano@uvcr.jp)