Enhancement in Light Extraction Efficiency of GaN-Based Light-Emitting Diodes Using Double Dielectric Surface Passivation

Chung-Mo Yang, Dong-Seok Kim, Yun Soo Park, Jae-Hoon Lee, Yong Soo Lee, Jung-Hee Lee

GaN Power Research Group, R&D Institute, Samsung LED Co., Ltd, Suwon, Republic of Korea.
School of Electrical Engineering and Computer Science Kyungpook National University, Daegu, Republic of Korea.

DOI: 10.4236/opj.2012.23028                

Abstract

SiO₂Al₂O₃ double dielectric stack layer was deposited on the surface of the GaN-based light-emitting diode (LED). The double dielectric stack layer enhances both the electrical characteristics and the optical output power of the LED because the first Al₂O₃ layer plays a role of effectively passivating the p-GaN surface and the second lower index SiO₂ layer increases the critical angle of the light emitted from the LED surface. In addition, the effect of the Fresnel reflection is also responsible for the enhancement in output power of the double dielectric passivated LED. The leakage current of the LED passivated with Al₂O₃ layer was -3.46 × 10^-11 A at -5 V, at least two and three orders lower in magnitude compared to that passivated with SiO₂ layer (-7.14 × 10^-9 A) and that of non-passivated LED (-1.9 × 10^-8 A), respectively, which indicates that the Al₂O₃ layer is very effective in passivating the exposed GaN surface after dry etch and hence reduces nonradiative recombination as well as reabsorption of the emitted light near the etched surface.

Keywords

GaN; Light-Emitting Diode (LED); Al₂O₃; PEALD; Passivation; Double Dielectric Stack Layer

1. Introduction

The III-nitrides are suitable materials for photoelectronic applications covering most of the electromagnetic spectrum due to their wide range of direct bandgap energy. Light emitting diodes (LEDs) are promising semiconductor devices for solid state lighting. Due to a remarkable development in LED fabrication technologies, the LEDs are now being commercialized in various applications such as traffic signals, full-color displays, back lighting in liquid-crystal displays, and so on [1]. However, further improvement in output power with long life time is still required for the GaN-based LED to be more efficiently used in such a field. The increase of the external quantum efficiency (η_EQE), which can be determined from the product of injection efficiency (η_inj) × radiative efficiency (η_rad) × extraction efficiency (η_ext), is the most important factor in achieving a high efficiency LED. η_inj and η_rad can be increased by improving the crystal quality and optimizing the epitaxial layer structure which maximizes the radiative recombination in active region. Surface passivation with appropriate dielectric layers is also necessary to avoid non-radiative recombination for high η_rad [2]. Special techniques such as control of surface roughness [3-5], preparation of patterned sapphire substrate (PSS) [6,7], application of flip-chip bonding [8-10], adaption of laser lift-off process [11], and formation of photonic crystal structure [12] are frequently used to improve η_ext, which can be increased by increasing the critical angle for the emitted light through an appropriate modification of the surface of the LED [13,14]. Anti-reflection (AR) coating of dielectric layers is frequently used to reduce the Fresnel reflection at the semiconductor-air interface in communication LEDs.

In this work, we report, in more detail, the development of passivation technique for the GaN-based LEDs by using double dielectric stack layer design is not optimized for the maximum anti-reflectivity.

2. Device Fabrication

Figure 1(a) shows the schematic LED configuration investigated in this work. The layer structure was grown on the patterned sapphire substrate (PSS) by metal-organic chemical vapor deposition (MOCVD). The blue LED structure contains low temperature grown GaN buffer layer, un-doped GaN layer, Si doped n-GaN layer, InGaN/GaN multi-quantum well active layer and Mg doped p-GaN cladding layer. The composition and thickness of InGaN/GaN multi-quantum well active layer was opti-

Conflicts of Interest

The authors declare no conflicts of interest.

References

[1]	T. Fujii, Y. Gao, R. Sharma, E. L. Hu, S. P. Den Baars and S. Nakamura, “Increase in the Extraction Efficiency of GaN-Based Light-Emitting Diodes via Surface Roughening,” Applied Physics Letters, Vol. 84, No. 6, 2004, pp. 855-857. doi:10.1063/1.1645992
[2]	C. M. Yang, D. S. Kim, S. G. Lee, J. H. Lee, Y. S. Lee and J. H. LEE, “Improvement in Electrical and Optical Performances of GaN-Based LED with SiO2/Al2O3 Double Dielectric Stack Layer,” IEEE Electron Device Letters, Vol. 33, No. 4, 2012, pp. 564-566. doi:10.1109/LED.2012.2185675
[3]	H.-W. Huang, C. C. Kao, J. T. Chu, S. C. Wang and C. C. Yu, “Improvement of InGaN-GaN Light-Emitting Diode Performance with a Nano-Roughened p-GaN Surface,” IEEE Photonics Technology Letters, Vol. 17, No. 5, 2005, pp. 983-985. doi:10.1109/LPT.2005.846741
[4]	C. M. Tsai, J. K. Sheu, W. C. Lai, Y. P. Hsu, P. T. Wang, C. T. Kuo, C. W. Kuo, S. J. Chang and Y. K. Su, “Enhanced Output Power in GaN-Based LEDs with Naturally Textured Surface Grown by MOCVD,” IEEE Electron Device Letters, Vol. 26, No. 7, 2005, pp. 464-466. doi:10.1109/LED.2005.851243
[5]	M. Y. Hsieh, C. Y. Wang, L. Y. Chen, T. P. Lin, M. Y. Ke, Y. W. Cheng, Y. C. Yu, C. P. Chen, D. M. Yeh, C. F. Lu, C. F. Huang, C. C. Yang and J. J. Huang, “Improvement of External Extraction Efficiency in GaNBased LEDs by SiO2 Nanosphere Lithography,” IEEE Electron Device Letters, Vol. 29, No. 7, 2008, pp. 658660. doi:10.1109/LED.2008.2000918
[6]	J. H. Lee, J. T. Oh, S. B. Choi, Y. C. Kim, H. I. Cho and J. H. Lee, “Enhancement of InGaN-Based Vertical LED with Concavely Patterned Surface Using Patterned Sapphire Substrate,” IEEE Photonics Technology Letters, Vol. 20, No. 5, 2008, pp. 345-347. doi:10.1109/LPT.2007.915648
[7]	J. H. Lee, J. T. Oh, Y. C. Kim and J. H. Lee, “Stress Reduction and Enhanced Extraction Efficiency of GaNBased LED Grown on Cone-Shape-Patterned Sapphire,” IEEE Photonics Technology Letters, Vol. 20, No. 18, 2008, pp. 1563-1565. doi:10.1109/LPT.2008.928844
[8]	C. F. Shen, S. J. Chang, W. S. Chen, T. K. Ko, C. T. Kuo and S. C. Shei, “Nitride-Based High-Power Flip-Chip LED with Double-Side Patterned Sapphire Substrate,” IEEE Photonics Technology Letters, Vol. 19, No. 10, 2007, pp. 780-782. doi:10.1109/LPT.2007.896574
[9]	S. H. Huang, R. H. Horng, K. S. When, Y. F. Lin, K. W. Yen and D. S. Wuu, “Improved Light Extraction of Nitride-Based Flip-Chip Light-Emitting Diodes via Sapphire Shaping and Texturing,” IEEE Photonics Technology Letters, Vol. 18, No. 24, 2006, pp. 2623-2625. doi:10.1109/LPT.2006.886823
[10]	O. B. Shchekin, J. E. Epler, T. A. Trottier, T. Margalith, D. A. Steigerwald, M. O. Holcomb, P. S. Martin and M. R. Krames, “High Performance Thin-Film Flip-Chip InGaNGaN Light-Emitting Diodes,” Applied Physics Letters, Vol. 89, No. 7, 2006, pp. 071109-071111. doi:10.1063/1.2337007
[11]	S. J. Wang, K. M. Usang, S. L. Chen, Y. C. Yang, S. C. Chang, T. M. Chen, B. W. Liou and C. H. Chen, “Use of Patterned Laser Liftoff Process and Electroplating Nickel Layer for the Fabrication of Vertical-Structured GaNBased Light-Emitting Diodes,” Applied Physics Letters, Vol. 87, 2005, p. 011111. doi:10.1063/1.1993757
[12]	H. W. Huang, C. H. Lin, Z. K. Huang, K. Y. Lee, C. C. Yu and H. C. Kuo, “Improved Light Output Power of GaN-Based Light-Emitting Diodes Using Double Photonic Quasi-Crystal Patterns,” IEEE Electron Device Letters, Vol. 30, No. 11, 2009, pp. 1152-1154. doi:10.1109/LED.2009.2029985
[13]	M. F. Schubert, F. W. Mont, S. Chhajed, D. J. Poxson, J. K. Kim and E. F. Schubert, “Design of Multilayer Antireflection Coatings Made from Co-Sputtered and LowRefractive-Index Materials by Genetic Algorithm,” Optics Express, Vol. 16, No. 8, 2008, pp. 5290-5298. doi:10.1364/OE.16.005290
[14]	J.-Q. Xi, M. F. Schubert, J. K. Kim, E. F. Schubert, M. Chen, S.-Y. Lin, W. Liu and J. A. Smart, “Optical ThinFilm Materials with Low Refractive Index for Broadband Elimination of Fresnel Reflection,” Nature Photonics, Vol. 1, No. 3, 2007, pp. 176-179.
[15]	S.-J. So and C.-B. Park, “Improvement of Brightness with Al2O3 Passivation Layers on the Surface of InGaN/GaNBased Light-Emitting Diode Chips,” Thin Solid Film, Vol. 516, No. 8, 2008, pp. 2031-2034. doi:10.1016/j.tsf.2007.07.143
[16]	C. Ostermaier, H.-C. Lee, S.-Y. Hyun, S.-I. Ahn, K.-W. Kim, H.-I. Cho, J.-B. Ha and J.-H. Lee, “Interface Characterization of ALD Deposited Al2O3 on GaN by CV Method,” Physica Status Solidi, Vol. 5, No. 6, 2008, pp. 1992-1994.
[17]	Y. Li, X. Y. Yi, X. D. Wang, J. X. Guo, L. C. Wang, G. H. Wang, F. H. Yang, Y. P. Zeng and J. M. Li, “Plasma Induced Damage in GaN-Based Light Emitting Diodes,” SPIE Proceedings, Vol. 6841, 2007, p. 68410x. doi:10.1117/12.759809
[18]	H. S. Yang, S. Y. Han, K. H. Baik and S. J. Pearton, “Effect of Inductively Coupled Plasma Damage on Performance of GaN-InGaN Multiquantum-Well Light-Emitting Diodes,” Applied Physics Letters, Vol. 86, 2005, p. 102104. doi:10.1063/1.1882749
[19]	E. F. Schubert, “Light-Emitting Diodes,” 2nd Edition, Cambridge University Press, Cambridge, 2006. doi:10.1017/CBO9780511790546
[20]	K. Matocha, R. J. Gutmann and T. P. Chow, “Effect of Annealing on GaN-Insulator Interfaces Characterized by Metal-Insulator-Semiconductor Capacitors,” IEEE Transactions on Electron Devices, Vol. 50, No. 5, 2003, pp. 12001204. doi:10.1109/TED.2003.813456