Significant Improvement in Output Power of UV LEDs
Flip-chip mounted UV LED chip
Output power of a test LED at 325 nm
Spectrum of a 325 nm LED without parasitic emission at longer wavelengths
LEDs in the UV spectral range are fabricated from AlGa(In)N epitaxial layer stacks on a sapphire substrate that is transparent for UV light. Crystallographic defects reduce the efficiency of light generation and thus the output power of the LEDs. These defects originate from the UV-transparent buffer layer between substrate and light emitting region. Theoretical calculations show that a reduction of the dislocation density from 2 x 1010 cm-2 to 5 x 109 cm-2 should result in a tenfold increase of the output power.
An important result has been achieved by FBH in cooperation with the group of Prof. Kneissl at TU Berlin: by optimizing the AlN base layers and the AlGaN structures grown on top of them, the output power of LEDs emitting around 320 nm increased from 23 µW to 0,53 mW. This was accomplished even without any additional measures to improve the light extraction. With this result, the gap to the leading groups in the world has been closed and the basis for the further increase of output power as well as the development of LEDs at even shorter wavelengths has been established.
Publications:
T. Kolbe, T. Sembdner, A. Knauer, V. Kueller, H. Rodriguez, S. Einfeldt, P. Vogt, M. Weyers, and M. Kneissl "Carrier injection in InAlGaN single and multi-quantum-well ultraviolet light emitting diodes" phys. stat. sol. (c), vol. 7, no. 7-8, pp. 2196-2198 (2010).
T. Kolbe, T. Sembdner, A. Knauer, V. Kueller, H. Rodriguez, S. Einfeldt, P. Vogt, M. Weyers, and M. Kneissl "(In)AlGaN deep ultraviolet light emitting diodes with optimized quantum well width" phys. stat. sol. (a), vol. 207, no. 9, pp. 2198-2200 (2010).
FBH research: 10.09.2010