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p-type doping concentrations：
1 ×1018cm-3 for 0.5 × 10-2 cm2 Ω
ρc,p−GaN 增加可以減少熱的產生
Fig.6 Calculated light emission patterns according to the
contact resistance ρc,p−GaN of the p-type GaN layer.
ρc,p−GaN are (a) 0.1 × 10−2 Ω cm2, (b) 0.5 × 10−2 Ω cm2,
and (c) 1.0 × 10−2 Ω cm2, respectively.
Simulation
Fig.7 Light intensity distributions calculated at
the top surfaces of LEDs for different electrode
patterns. (a) Bar-shaped pattern. (b) U-shaped Fig.8 Measured light intensity distributions on
pattern.
the top surfaces of LEDs for different
electrode patterns by optical microscopes. (c)
and (d) show the signal processed data of (a)
and (b), respectively, to see the light intensity
distribution more clearly.
3.14V
3.27V
Fig.9Measured I–V curves for the two different
electrode patterns shown in Fig. 8(a) and (b).
Fig.10 Measured light output L–I curves for
the two different electrode patterns shown in
Fig. 8(a) and (b).
Fig.11 Measured I–V curves for the two
different electrode patterns before and after
the current injection of 400 mA for 5 min.
Fig.12 Degradation of output powers before
and after the current injection of 400 mA for
5 min.
Fig.13 (a) Measured photograph of an ESD-damaged
LED chip. Simulated results of (b) current distribution
in the TME layer. (c) Current flow at A–A’ cross
sectional view. (d) Current distribution in the n-GaN
buffer layer.
Conclusion
•We have proposed a new method analyzing the 3-D current
spreading in LED chips and developed a design software tool.
•We confirmed that the distribution of the experimental light
intensity and the ESD-induced surface defects agree well with our
analysis of the results.
•It was also found that the electrode pattern affects the performance
of LEDs in view of light intensity distribution, saturation of light
power, and device reliability.
References
Sungmin Hwang and Jongin Shim, Member, IEEE,” A Method for
Current Spreading Analysis and Electrode Pattern Design in LightEmitting Diodes ,“IEEE TRANSACTIONS ON ELECTRON
DEVICES, VOL. 55, NO. 5, MAY 2008.