TY - JOUR
T1 - Improved electrical and optical properties of vertical GaN LEDs using fluorine-doped ITO/Al ohmic reflectors
AU - Lee, Wan Ho
AU - Chae, Dong Ju
AU - Kim, Dong Yoon
AU - Kim, Tae Geun
N1 - Funding Information:
Manuscript received March 29, 2011; revised June 20, 2011; accepted June 24, 2011. Date of current version August 19, 2011. This work was supported in part by a National Research Foundation grant funded by the Ministry of Education, Science and Technology, under Project KRF-2008-D00074, by the Leading Foreign Research Institute Recruitment Program under Grant 2010-00218, and by the Seoul Research & Business Development Program under Grant WR080951.
PY - 2011
Y1 - 2011
N2 - In this paper, we report on the effects of indium-doped tin oxide (ITO) film surface conditions on the electrical and optical properties of ITO/Aluminium(Al) ohmic reflectors used in vertical GaN light-emitting diodes (LEDs). First, four ITO films annealed at 400 °C, 500 °C, 600 °C, and 700 °C for 5 min by a rapid thermal process were characterized; the best performance, with a transmittance of 91% at 460 nm, a resistivity of 8.2 × 10 -4 Ω·cm, and a root mean square surface roughness of 2.49 nm, was obtained from the sample annealed at 500 °C. Then, CF4 plasma was applied to the surface of the ITO before the Al deposition, not only to clean the ITO surface, and thereby increase the reflectance of the ITO/Al, but also to reduce the contact resistivity by preventing the Al-O bonding and inducing an Al-F bonding. The ITO work function is effectively increased by fluorine doping, which eventually reduces the Schottky barrier height between the ITO and the p-GaN. As a result, the reflectance of the ITO/Al increased up to 85% from 71% at 460 nm; its contact resistivity was down to 2.03 × 10-3 Ω·cm 2 from 9.07 × 10-3 Ωcm2 via the CF4 plasma treatment. Finally, we applied the fluorinated ITO/Al metal to vertical GaN LEDs, which enabled the light output power to be enhanced by 72% at 60 mA compared with those with nontreated ITO/Al reflectors.
AB - In this paper, we report on the effects of indium-doped tin oxide (ITO) film surface conditions on the electrical and optical properties of ITO/Aluminium(Al) ohmic reflectors used in vertical GaN light-emitting diodes (LEDs). First, four ITO films annealed at 400 °C, 500 °C, 600 °C, and 700 °C for 5 min by a rapid thermal process were characterized; the best performance, with a transmittance of 91% at 460 nm, a resistivity of 8.2 × 10 -4 Ω·cm, and a root mean square surface roughness of 2.49 nm, was obtained from the sample annealed at 500 °C. Then, CF4 plasma was applied to the surface of the ITO before the Al deposition, not only to clean the ITO surface, and thereby increase the reflectance of the ITO/Al, but also to reduce the contact resistivity by preventing the Al-O bonding and inducing an Al-F bonding. The ITO work function is effectively increased by fluorine doping, which eventually reduces the Schottky barrier height between the ITO and the p-GaN. As a result, the reflectance of the ITO/Al increased up to 85% from 71% at 460 nm; its contact resistivity was down to 2.03 × 10-3 Ω·cm 2 from 9.07 × 10-3 Ωcm2 via the CF4 plasma treatment. Finally, we applied the fluorinated ITO/Al metal to vertical GaN LEDs, which enabled the light output power to be enhanced by 72% at 60 mA compared with those with nontreated ITO/Al reflectors.
KW - Light-emitting diodes
KW - Schottky barrier height
KW - plasma treatment
KW - reflectance
KW - resistivity
KW - transmittance
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U2 - 10.1109/JQE.2011.2161271
DO - 10.1109/JQE.2011.2161271
M3 - Article
AN - SCOPUS:80052396212
VL - 47
SP - 1277
EP - 1282
JO - IEEE Journal of Quantum Electronics
JF - IEEE Journal of Quantum Electronics
SN - 0018-9197
IS - 10
M1 - 5940194
ER -