SCIENCE CHINA
Physics, Mechanics & Astronomy
© Science China Press and Springer-Verlag Berlin Heidelberg 2011 phys.scichina.com www.springerlink.com
*Corresponding author (email: herofate@126.com)
• Research Paper •
October 2011 Vol.54 No.10: 1787–1790
doi: 10.1007/s11433-011-4461-3
Enhancement of light output powers of GaN-based light emitting
diodes with textured indium tin oxide transparent layer by using
corrosive liquid
LI Yun
1
, LI XiaoChan
2
, ZHANG Tao
2
, HE AnHe
3
, HU CanDong
1
, WANG Xin
1
, HE Miao
1*
,
ZHANG Yong
1
, NIU QiaoLi
1
, ZHAO LingZhi
1
, LI ShuTi
1
& CHEN XianWen
1
1
Key Laboratory of Electroluminescent Devices of Guangdong Provincial Education Department, Institute of Optoelectronic Materials &
Technology, South China Normal University, Guangzhou 510631, China;
2
College of Information Science and Engineering, Wuhan University of Science & Technology, Wuhan 430081, China;
3
Sanan Optoelectronics Co., Ltd., Xiamen 361009, China
Received December 24, 2010; accepted January 18, 2011; published online August 5, 2011
In order to promote the light output powers of GaN-based light emitting diodes (LEDs), two kinds of novel corrosive liquids
have been developed in this paper to roughen the surface of the indium tin oxide (ITO) current spreading layer of LEDs. As a
result, the textured transparent ITO layer greatly enhanced the external quantum efficiency of the LEDs. Provided that a wafer
sample was dipped in a kind of corrosive liquid developed by us for only about 60 s, the light output powers of the LEDs can
be promoted by 24.7%, compared with conventional GaN-based LEDs. It is obvious that the presented method is simple, rapid
and cost-effective.
GaN-based light emitting diodes (LEDs), corrosive liquid, light output power, textured ITO
PACS: 85.30.De, 71.55.Eq, 73.40.Kp, 85.60.Jb
1 Introduction
III-nitride-based materials have the property of wide direct
band gap and applications for blue and ultraviolet wave-
length fields [1]. In recent years, high-efficiency GaN-based
light emitting diodes (LEDs), made from III-nitride-based
materials, have attracted much interest because of their
wide-ranging applications, such as traffic lights, full color
displays, backlights, exterior automobile lighting, and sol-
id-state lighting [2]. And the trend that the GaN-based
LEDs will replace incandescent bulbs and fluorescent lamps
is becoming more and more obvious [3].
However, the light extraction efficiency from high-effi-
ciency GaN-based LEDs is restricted by the total internal
reflection (TIR) due to large difference in refractive index
between the GaN film (n
GaN
=2.5) and air (n
air
=1) [4]. Ac-
cording to Snell’s law, the light TIR critical angle
(
c
=sin
1
(n
air
/n
GaN
)) on the interface between GaN and air is
about 23.5°. The photons emitted at angles larger than the
critical angle are rebounded back from the interface be-
tween GaN and air, reabsorbed by the light-emitting layer
and confined internally, which reduces the external quantum
efficiency. It can be easily calculated that only about 4% of
the photons emitted from the LED active region can escape
from the surface [5]. Therefore, how to extract more pho-
tons, generated inside the active region, out of the LED is
the pivotal issue.
Several approaches have been implemented to improve
the light extraction of GaN-based LEDs, such as employing
photonic crystals structures [6], introducing a highly trans-
parent p-contact layer [7], and surface roughening [8]. And