title: Wafer-scale surface roughening for enhanced light extraction of high power AlGaInP-based light-emitting diodes.
abstract: A new approach to surface roughening was established and optimized in this paper for enhancing the light extraction of high power AlGaInP-based LEDs, by combining ultraviolet (UV) assisted imprinting with dry etching techniques. In this approach, hexagonal arrays of cone-shaped etch pits are fabricated on the surface of LEDs, forming gradient effective-refractive-index that can mitigate the emission loss due to total internal reflection and therefore increase the light extraction efficiency. For comparison, wafer-scale FLAT-LEDs without any surface roughening, WET-LEDs with surface roughened by wet etching, and DRY-LEDs with surface roughened by varying the dry etching time of the AlGaInP layer, were fabricated and characterized. The average output power for wafer-scale FLAT-LEDs, WET-LEDs, and DRY3-LEDs (optimal) at 350 mA was found to be 102, 140, and 172 mW, respectively, and there was no noticeable electrical degradation with the WET-LEDs and DRY-LEDs. The light output was increased by 37.3% with wet etching, and 68.6% with dry etching surface roughening, respectively, without compromising the electrical performance of LEDs. A total number of 1600 LED chips were tested for each type of LEDs. The yield of chips with an optical output power of 120 mW and above was 0.3% (4 chips), 42.8% (684 chips), and 90.1% (1441 chips) for FLAT-LEDs, WET-LEDs, and DRY3-LEDs, respectively. The dry etching surface roughening approach developed here is potentially useful for the industrial mass production of wafer-scale high power LEDs.
authors.forename: Hyeong-Ho
authors.initials: HH
authors.lastname: Park
authors.forename: Xin
authors.initials: X
authors.lastname: Zhang
authors.forename: Yunae
authors.initials: Y
authors.lastname: Cho
authors.forename: Dong-Wook
authors.initials: DW
authors.lastname: Kim
authors.forename: Joondong
authors.initials: J
authors.lastname: Kim
authors.forename: Keun Woo
authors.initials: KW
authors.lastname: Lee
authors.forename: Jehyuk
authors.initials: J
authors.lastname: Choi
authors.forename: Hee Kwan
authors.initials: HK
authors.lastname: Lee
authors.forename: Sang Hyun
authors.initials: SH
authors.lastname: Jung
authors.forename: Eun Jin
authors.initials: EJ
authors.lastname: Her
authors.forename: Chang Hwan
authors.initials: CH
authors.lastname: Kim
authors.forename: A-Young
authors.initials: AY
authors.lastname: Moon
authors.forename: Chan-Soo
authors.initials: CS
authors.lastname: Shin
authors.forename: Hyun-Beom
authors.initials: HB
authors.lastname: Shin
authors.forename: Ho Kun
authors.initials: HK
authors.lastname: Sung
authors.forename: Kyung Ho
authors.initials: KH
authors.lastname: Park
authors.forename: Hyung-Ho
authors.initials: HH
authors.lastname: Park
authors.forename: Hi-Jung
authors.initials: HJ
authors.lastname: Kim
authors.forename: Ho Kwan
authors.initials: HK
authors.lastname: Kang