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 high-power 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 Chip Size ： 1mm * 1 mm. Fig. 1 Lateral GaN/InGaN LED devices selected for analysis and comparison. Chip Size ： 1mm * 1 mm.

Table 1: Extracted material and structural parameters 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 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.

APPLIED PHYSICS LETTERS 93, 111907 2008 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 light-emitting 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 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. 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. 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.