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Effect of the Electrode Pattern on
Current Spreading and Driving Voltage
in a GaN/Sapphire LED Chip
李仁凱
Outline
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Introduction
Results and Discussion
Conclusions
References
Introduction
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The numerical results current distributions for the striped pattern pelectrode are well consistent with the optical emission patterns taken
from emission images.
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A desirable uniformity of the current distribution in the active layer
can be obtained by the appropriate arrangement of p- and n-electrode
patterns.
Results and Discussion
Figure 1. Shematic illustration of a cross-sectional view of the device along the
stripe direction.
Results and Discussion
Figure 3. Micrographs of experimental optical emissions when operated at 30 mA
for (a) the short-stripe case and (b) the long-stripe case. The related chip
dimensions are also marked.
Results and Discussion
Figure 2. Relation of input power to (a) driving voltage and (b) wall-plug efficiency
for both short- and long stripe LED from the experiments.
Results and Discussion
Figure 4. Isoline diagrams of simulated current densities in the active layer when
operated at 30 mA for (a) the short-stripe case and (b) the long- stripe case.
Results and Discussion
Figure 5.
Normalized experimental optical emission densities solid symbols and
currents from the simulation hollow symbols along the line bar in Fig. 3 at
20 mA squares and 30 mA triangles for a the short-stripe case and b the
long-stripe case.
Results and Discussion
Figure 6. Top view of the simulated current vectors of the ITO, p-GaN, and n-GaN
layers when operated at 30 mA for (a) the short stripe case and (b) the
long-stripe case.
Results and Discussion
Figure 7. Simulated relations of the p-electrode stripe length to current density in the
active layer and the driving voltage of the LED at an input current of 30 mA.
The difference between the maximum and minimum current density and the
standard deviation of current density in the active layer are marked by hollow
and solid squares, respectively. The driving voltage of the LED is marked by
solid circular symbols. The inset isoline diagram shows the calculated current
density distribution in the active layer for a stripe length of 285 μm.
Results and Discussion
Figure 8. (a) Lengths of the n-electrode around the chip marked from no. 1 to no. 9; top view of
the 3D current vectors in the n-GaN layers at 30 mA from the simulation when the nelectrode length reaches the (b) no. 2, © no. 6, and (e) no. 9 positions, respectively. (d)
A cross-sectional view along the AB line in (c ).
Results and Discussion
Figure 9. Relations of different n-electrode lengths to current density in the active layer
and the driving voltage of the LED at an input current of 30 mA from the
simulation.
Results and Discussion
Figure 10. (a) Diagram of the p- and n-electrode patterns, and (b) 3D current arrows in
the active layer for the no. 6 length n-electrode when operated at 30 mA
from the simulation.
Results and Discussion
Figure 11. Relations of different n-electrode lengths with the current density in the
active layer and driving voltage of the LED at an input current of 30 mA
from the simulation for the p- and n-electrode patterns in Fig. 10a.
Conclusions
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A numerical simulation has been performed to investigate the effects
of p and n-electrode patterns on the current spreading and the driving
voltage of side-view GaN/sapphire LED chips.
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The influence of changing the p-electrode pattern on the current
spreading and the voltage drop is more significant than that made by
altering the n-electrode pattern.
References
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“Effect of the Electrode Pattern on Current Spreading and Driving Voltage in a
GaN/Sapphire LED Chip” Gwo-Jiun Sheu , Farn-Shiun Hwu , Jyh-Chen Chen ,
Jinn-Kong Sheu , and Wei-Chi Lai , Journal of The Electrochemical Society, 155 10
H836-H840 2008。