Improvement in efficiency droop of GaN-based light-emitting diodes by optimization of active regions

C. H. Wang; D. W. Lin; C. H. Chiu; S. P. Chang; Z. Y. Li; J. C. Li; H. C. Kuo; T. C. Lu; S. C. Wang

doi:10.1117/12.874935

9 February 2011 Improvement in efficiency droop of GaN-based light-emitting diodes by optimization of active regions

C. H. Wang, D. W. Lin, C. H. Chiu, S. P. Chang, Z. Y. Li, J. C. Li, H. C. Kuo, T. C. Lu, S. C. Wang

Proceedings Volume 7954, Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XV; 795408 (2011) https://doi.org/10.1117/12.874935
Event: SPIE OPTO, 2011, San Francisco, California, United States

Abstract

We had demonstrated several novel methods to improve efficiency droop behavior in GaN-based light-emitting diodes (LEDs). LEDs with different kinds of insertion layers (ILs) between the multiple quantum wells (MQWs) layer and n-GaN layer were investigated. By using low-temperature (LT, 780°C) n-GaN as IL, the efficiency droop behavior can be alleviated from 54% in reference LED to 36% from the maximum value at low injection current to 200 mA, which is much smaller than that of 49% in LED with InGaN/GaN short-period superlattices (SPS) layer. The polarization field in MQWs is found to be smallest in LED with InGaN/GaN SPS layer. However, the V-shape defect density, about 5.3×10⁸ cm^-2, in its MQWs region is much higher than that value of 2.9×108 cm^-2 in LED with LT n-GaN layer, which will lead to higher defect-related tunneling leakage of carriers. Therefore, we can mainly assign this alleviation of efficiency droop to the reduction of dislocation density in MQWs region rather than the decrease of polarization field. At second part, LEDs with graded-thickness multiple quantum wells (GQW) was designed and found to have superior hole distribution as well as radiative recombination distribution by simulation modeling. Accordingly, the experimental investigation of electroluminescence spectrum reveals additional emission from the previous narrower wells within GQWs. Consequently, the efficiency droop can be alleviated to be about 16% from maximum at current density of 30 A/cm² to 200 A/cm². Moreover, the light output power is enhanced by 35% at 20 A/cm².

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C. H. Wang, D. W. Lin, C. H. Chiu, S. P. Chang, Z. Y. Li, J. C. Li, H. C. Kuo, T. C. Lu, and S. C. Wang "Improvement in efficiency droop of GaN-based light-emitting diodes by optimization of active regions", Proc. SPIE 7954, Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XV, 795408 (9 February 2011); https://doi.org/10.1117/12.874935

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KEYWORDS

Light emitting diodes

Quantum wells

Electroluminescence

Gallium nitride

Surface plasmons

Electrons

Dielectric polarization

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