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A Method for Current Spreading Analysis
and Electrode Pattern Design in LightEmitting Diodes
Sungmin Hwang and Jongin Shim, Member, IEEE
IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 55, NO. 5,
MAY 2008
報告者：B.J.Hu
Outline
I.
II.
III.
IV.
V.
Introduction
Experimental
Results and Discussion
Conclusion
References
Introduction
We report a method that informs both the 2-D light
emission pattern on an entire LED surface and a 3-D current
flow in a LED structure.
The current crowding effect is directly related to the LED
chip reliability.
Experimental
p-pad
ITO
p-GaN
p-Al0.15GaN0.85
MQW
n-GaN
Buffer layer
Sapphire
Chip size：320μm* 320μm
n-pad
Fig.1 Schematic view of an InGaN/GaN LED
structure.
Fig.2 Three-dimensional circuit
modeling of a LED structure.
l (1 qN ) l
R  R sh 
w
t
w
Rsh：sheet resistance
L：length
w：width
t：thickness
N：carrier concentration
μ：carrier mobility
RESULTS AND DISCUSSION
Simulation and experimental
Fig.3 (a) Calculated light emission pattern. (b) Numeric data of
the measured light emission intensity at the injection current of
50 μA. The chip size is 320 μm × 320 μm.
doping concentrations：
1.5 × 1019 cm−3 for 10 [Ω/ □]
5 × 1018 cm−3 for 32 [Ω/ □]
3 × 1018 cm−3 for 45 [Ω/ □]
Fig.4 Calculated current distribution of LEDs according
to the sheet resistance Rsh,n−GaN of the n-type GaN
layer. (a) 45 [Ω/ □]. (b) 32 [Ω/ □]. (c) 10 [Ω/ □].
TME film thicknesses：
5 nm for 36 [Ω/ □]
10 nm for 18 [Ω/ □]
20 nm for 9 [Ω/ □]
Fig.5 Calculated light emission patterns according
to the sheet resistance of the TME layer Rsh,TME.
(a) 9 [Ω/□]. (b) 18 [Ω/ □]. (c) 36 [Ω/ □].