Impact of roughening density on the light extraction efficiency of thin-film flip-chip ultraviolet LEDs grown on SiC

Burhan K. Saifaddin, Michael Iza, Humberto Foronda, Abdullah Almogbel, Christian J. Zollner, Feng Wu, Ahmed Alyamani, Abdulrahman Albadri, Shuji Nakamura, Steven P. DenBaars, James S. Speck

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12 Scopus citations


Discovering ways to increase the LED light extraction efficiency (LEE) should help create the largest performance improvement in the power of UV AlGaN LEDs. Employing surface roughening to increase the LEE of typical AlGaN UV LEDs is challenging and not well understood, yet it can be achieved easily in AlGaN LEDs grown on SiC. We fabricate thin-film UV LEDs (~294-310 nm) grown on SiC—with reflective contacts and roughened emission surface—to study and optimize KOH roughening of N-face AlN on the LEE as a function of roughened AlN pyramid size and KOH solution temperature. The LEE increased the most (2X) when the average AlN pyramid base diagonals (d) were comparable to the electroluminescence (EL) wavelength in the AlN layer (d ~λEL; 42–52 pyramids/µm2), but the LEE enhancement diminished when d was much larger than λEL (d ~5.5λEL; 2–3 pyramids/µm2). The UV LEDs had a 10 nm p-GaN contact layer, and the forward voltage was ~6 V at ~8 A/cm2, with a voltage efficiency (VE) of ~70%. The VE of the LEDs did not change after KOH roughening. This work suggests important implications to increase the LEE of AlGaN LEDs.
Original languageEnglish (US)
Pages (from-to)A1074
JournalOptics Express
Issue number16
StatePublished - Jul 10 2019
Externally publishedYes

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics

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