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Relationship between thermal and
luminance distributions in high-power
lateral GaN/InGaN light-emitting diodes
D.P. Han, J.I. Shim and D.S. Shin
ELECTRONICS LETTERS , 18th March 2010 , Vol. 46 No. 6
J.K. Lee
Outline
• Introduction
• Experiment
• Results and discussion
• Conclusion
Introduction
Relationship between the luminance and thermal distributions in highpower lateral GaN/InGaN blue LEDs by using a current density
distribution analysis and comparing two LED devices with different
electrode designs.
Experiment
P
P
N
N
Fig. 1 Lateral GaN/InGaN LED devices selected for analysis and comparison.
Chip Size ： 1mm * 1 mm.
Experiment
Table 1: Extracted material and structural parameters
Rsh,TME : lateral resistance of TME.
Rsh,n-GaN : lateral resistance of n-GaN.
Rsh,p-GaN : lateral resistance of p-GaN.
ρc : specific contact resistance between TME and p-GaN.
β: exponential junction parameter.
Is : reverse saturation current.
Results and discussion
Fig. 2 Luminance distributions obtained by using simulator based on threedimensional
electrical circuit model when current of 400 mA is injected (Figs 2a and b), and
luminance distributions taken by CCD camera when current of 400 mA is injected
(Figs 2c and d)
Results and discussion
85℃
90℃
Fig. 3 Thermal images taken by an infrared camera when a current of 400 mA is
injected (Figs 3a and b), and thermal image after image processing (Figs 3c and d).
Results and discussion
A
B
Fig. 4 Measured light-current curves for two different LED devices shown in Figs 1a
and b.
Conclusion
It can be concluded that the current-density distribution is essential in
determining the luminance and thermal properties of high-power lateral
GaN LED devices.
We have also shown that poorer current spreading indicated by a smaller
emission area can eventually cause an earlier optical saturation in the
LED devices.
Simulation of current spreading for
GaN-based light-emitting diodes
Pei Wang, Wei Wei, Bin Cao, Zhiyin Gan, Sheng Liu
Optics & Laser Technology , 42 (2010) , 737–740
Outline
• Introduction
• Experiment
• Results and discussion
• Conclusion
Introduction
It has been reported that the reliability and light distribution are affected
by non-uniform current spreading.
The impact of different electrode patterns on the performance of LED
chips is investigated.
Experiment
Fig. 1. Schematics of the two LED chips with different electrode patterns.
Results and discussion
Fig. 2. Current density distribution in the active layer of sample A (a) and sample B (b)
under the injection current of 300 mA.
Results and discussion
Fig. 3. Diode temperature distribution of sample A (a) and sample B (b) under the
injection current of 300 mA.
Results and discussion
Fig. 4. Measured and simulated I–V curves for sample A and sample B.
Results and discussion
Fig. 5. The L–I characteristics and the external quantum efficiency versus the injection
current of the LED chips.
Conclusion
It is found that increasing the number of p-electrodes in the interdigitated
electrode patterns improves the performance of the LED.
It is demonstrated that the electrode pattern plays an important role in the
design and fabrication of LED chips due to its influence on the current
spreading and then the optical and electrical performance of chips.
Improved thermal management of
GaN/sapphire
light-emitting
diodes
embedded in reflective heat spreaders
R. H. Horng, C. C. Chiang, H. Y. Hsiao, X. Zheng, D. S. Wuu, and H. I. Lin
APPLIED PHYSICS LETTERS 93, 111907 2008
Outline
• Introduction
• Experiment
• Results and discussion
• Conclusion
• References
Introduction
We have demonstrated an enhanced performance of GaN/sapphire lightemitting diode LED embedded in a reflective copper heat spreader.
Infrared thermal images confirm the GaN/sapphire LED with more
efficient heat extraction and better temperature uniformity.
Experiment
FIG. 1. Schematic fabrication sequences
of InGaN LED structure embeddedIn a
reflective Cu heat spreader : (a) a
conventional lateral-electrode LED, (b) a
transferring of chip to glass carrier,
followed by photoresist coating, (c) an
evaporation of Au/Cr/Ag mirror films,
(d) Cu electroplating over a cupshaped
reflector, and (e) a LED chip embedded
into reflective Cu heat spreader after
removing glass carrier and photoresist by
immersion of acetone.
Experiment
FIG. 2. SEM micrographs of fabrication sequences of InGaN LED structure embedded
in a reflective Cu heat spreader : (a) process step shown in Fig. 1(b) and (b) final
process step shown in Fig. 1(e).
Results and discussion
FIG. 3. (Color online) (a) Light output power and (b) power efficiency of LED with the
reflective Cu heat spreader as a function of the forward current, along with the case of
the conventional GaN LED. The inset shows their corresponding angular distribution of
emission patterns at 20 mA.
Results and discussion
FIG. 4. (Color online) Thermal images for InGaN/sapphire LED (a) without and (b)
with a reflective heat spreader, as well as the simulated thermal distribution for (c) the
former and (d) the latter, respectively.
Conclusion
Using the direct-electroformed Cu heat spreader module applied to the
conventional GaN/sapphire LED chip.
Improvement in the thermal management and optical performance. The
heat generated from the LED chip is efficiently extracted due to a
reasonably large metal spreader.
References
1. D.P. Han, J.I. Shim and D.S. Shin, “ Relationship between thermal and luminance
distributions in high-power lateral GaN/InGaN light-emitting diodes ”,
ELECTRONICS LETTERS , 18th March 2010 , Vol. 46 No. 6.
2. Pei Wang, Wei Wei, Bin Cao, Zhiyin Gan, Sheng Liu, “ Simulation of current
spreading for GaN-based light-emitting diodes ” , Optics & Laser Technology , 42
(2010) , 737–740.
3. R. H. Horng, C. C. Chiang, H. Y. Hsiao, X. Zheng, D. S. Wuu, and H. I. Lin, “
Improved thermal management of GaN/sapphire light-emitting diodes
embedded in reflective heat spreaders ” , APPLIED PHYSICS LETTERS 93,
111907 2008.