scholarly journals Temperature dependent efficiency droop in GaInN light-emitting diodes with different current densities

2012 ◽  
Vol 100 (8) ◽  
pp. 081106 ◽  
Author(s):  
David S. Meyaard ◽  
Qifeng Shan ◽  
Jaehee Cho ◽  
E. Fred Schubert ◽  
Sang-Heon Han ◽  
...  
Keyword(s):  
Light Emitting Diodes ◽  
Efficiency Droop ◽  
Temperature Dependent ◽  
Light Emitting ◽  
Current Densities

Approaches Towards the Ultimate Luminous Output Power of Light-Emitting Diodes: Bottlenecks and Remedies

2015 ◽  
Author(s):  
Xiaokun Zhang ◽  
Xiao-Dong Xiang ◽  
Yong Xiang
Keyword(s):  
Output Power ◽  
Light Emitting Diodes ◽  
Thermal Runaway ◽  
Efficiency Droop ◽  
Injection Current ◽  
Light Emitting ◽  
Excessive Heat ◽  
High Injection ◽  
Current Densities ◽  
The Cost

Although light-emitting diodes (LEDs) hold great promises for high-efficiency lighting applications, the cost per lumen still poses a challenge for LEDs to fast penetrate into the markets. Increasing the output power per LED chip reduces the number of chips required for a specific luminous flux, thus reducing the cost of LED luminaires. However, it is well known that the luminous output power of LEDs (Pout) cannot be enhanced simply by increasing the injection current density (Jinj) due to efficiency droop. Extensive efforts have been made towards avoiding efficiency droop at high injection current densities (e.g., Jinj > 50 A/cm2). Gardner et al. reported a double-heterostructure LED with an external quantum efficiency (EQE) of 40% at 200 A/cm2. Xie et al. introduced an electron-blocking layer into the LED devices and the EQE peak occurred at 900 A/cm2 approximately. Nevertheless, the EQE is always lower than 100%, excessive heat will accumulate in LEDs at high current densities and increase the junction temperatures, which will damage the device and limit its luminous output power and lifetime. In this paper, the recombination mechanism in the LED active area is analyzed and an analytic relationship between Pout and Jinj is proposed. The calculated results show that the best Pout currently achieved is far lower than its potential value. The temperature dependence of the Pout-Jinj relationship is also calculated and the thermal state of LEDs at high injection current densities predicted. The results demonstrate that LED luminaires with thermal management based on conventional fin-shaped heat sinks suffer from thermal runaway due to excessive heat accumulation before reaching their ultimate output power. The gap between the existing and predicted Pout is mainly due to thermal runaway of LED devices at high injection current densities, instead of efficiency droop. Therefore, the short-term solution of LED luminous output power enhancement should be better cooling of LED modules, such as jet/spray cooling, heat pipe cooling, or 3D embedded two-phase cooling. Long-term solutions continue to focus on reducing the efficiency droop with improved LED device structures and advanced materials.

Temperature-dependent efficiency droop behaviors of GaN-based green light-emitting diodes

2013 ◽  
Vol 22 (4) ◽  
pp. 047805 ◽  
Author(s):  
Rong Jiang ◽  
Hai Lu ◽  
Dun-Jun Chen ◽  
Fang-Fang Ren ◽  
Da-Wei Yan ◽  
...  
Keyword(s):  
Light Emitting Diodes ◽  
Green Light ◽  
Efficiency Droop ◽  
Temperature Dependent ◽  
Light Emitting

scholarly journals High-brightness lasing at submicrometer enabled by droop-free fin light-emitting diodes (LEDs)

2020 ◽  
Vol 6 (33) ◽  
pp. eaba4346
Author(s):  
Babak Nikoobakht ◽  
Robin P. Hansen ◽  
Yuqin Zong ◽  
Amit Agrawal ◽  
Michael Shur ◽  
...  
Keyword(s):  
Output Power ◽  
Light Emitting Diodes ◽  
Efficiency Droop ◽  
Light Extraction Efficiency ◽  
Electrical Currents ◽  
High Brightness ◽  
Light Emitting ◽  
Recombination Processes ◽  
Current Densities ◽  
New Generation

“Efficiency droop,” i.e., a decline in brightness of light-emitting diodes (LEDs) at high electrical currents, limits the performance of all commercial LEDs and has limited the output power of submicrometer LEDs and lasers to nanowatts. We present a fin p-n junction LED pixel that eliminates efficiency droop, allowing LED brightness to increase linearly with current. With record current densities of 1000 kA/cm2, the LEDs transition to lasing, with brightness over 20 μW. Despite a light extraction efficiency of only 15%, these devices exceed the output power of any previous electrically driven submicrometer LED or laser pixel by 100 to 1000 times while showing comparable external quantum efficiencies. Modeling suggests that spreading of the electron-hole recombination region in fin LEDs at high injection levels suppresses the nonradiative Auger recombination processes. Further refinement of this design is expected to enable a new generation of high-brightness LED and laser pixels for macro- and microscale applications.

scholarly journals Temperature-dependent efficiency droop of blue InGaN micro-light emitting diodes

2014 ◽  
Vol 105 (17) ◽  
pp. 171107 ◽  
Author(s):  
Pengfei Tian ◽  
Jonathan J. D. McKendry ◽  
Johannes Herrnsdorf ◽  
Scott Watson ◽  
Ricardo Ferreira ◽  
...  
Keyword(s):  
Light Emitting Diodes ◽  
Efficiency Droop ◽  
Temperature Dependent ◽  
Light Emitting

Efficiency Re-Climbing in High-Current Droop Regime for Gallium-Nitride-based Light-Emitting Diodes

2015 ◽  
Vol 24 (03n04) ◽  
pp. 1520008
Author(s):  
Guan-Bo Lin ◽  
E. Fred Schubert
Keyword(s):  
Light Emitting Diodes ◽  
Efficiency Droop ◽  
Hole Injection ◽  
Field Ionization ◽  
Cryogenic Temperatures ◽  
Light Emitting ◽  
Operating Current ◽  
Current Densities ◽  
P Type ◽  
Distinct Increase

The efficiency droop in GaInN/GaN blue light-emitting diodes (LEDs) usually commences at current density around 10 A/cm2 and the efficiency decreases monotonically after the droop onset. GaN-based LEDs suffer seriously, at typical operating current densities (10–100 A/cm2), by the efficiency droop. Efficiency re-climbing is observed in the typical droop regime at cryogenic temperatures below 125K. The “efficiency re-climbing” coincides with a distinct increase in device conductivity, which is mainly attributed to an enhancement in p-type conductivity due to field ionization of acceptors. The “efficiency re-climbing” phenomenon implies an approach of solving efficiency droop by enhancing hole injection by external electric field.

scholarly journals Effect of Trapezoidal-Shaped Well on Efficiency Droop in InGaN-Based Double-Heterostructure Light-Emitting Diodes

2012 ◽  
Vol 2012 ◽  
pp. 1-5 ◽  
Author(s):  
Ray-Ming Lin ◽  
Mu-Jen Lai ◽  
Liann-Be Chang ◽  
Chou-Hsiung Huang ◽  
Chang-Ho Chen
Keyword(s):  
Quantum Efficiency ◽  
Current Density ◽  
Light Emitting Diodes ◽  
Internal Quantum Efficiency ◽  
Well Being ◽  
Efficiency Droop ◽  
Maximum Efficiency ◽  
Light Emitting ◽  
Double Heterostructure ◽  
Current Densities

We investigated the effects of different well shapes on the external quantum efficiency (EQE) and the efficiency droop in wide-well InGaN/GaN double-heterostructure light-emitting diodes. For forward current densities in the measurement range of greater than 135 A/cm2, the device featuring a trapezoidal well exhibited improved EQEs and alleviative efficiency droop, relative to those of the device featuring a rectangular well. The decreased Auger loss has been proposed as the main reason for the greater maximum efficiency that occurred at high current density (>50 A/cm2). For the devices incorporating trapezoidal and rectangular wells, the EQEs at 200 A/cm2decreased by 14 and 40%, respectively, from their maximum values, resulting in the EQE at a current density of 200 A/cm2of the device featuring a trapezoidal well being 17.5% greater than that featuring a rectangular well. These results suggest that, in addition to the decreased Auger loss, the alleviation in efficiency droop at higher current densities might be due to higher internal quantum efficiency resulted from the improved carrier injection efficiency of the trapezoidal well.

Asymmetry of carrier transport leading to efficiency droop in GaInN based light-emitting diodes

2011 ◽  
Vol 99 (25) ◽  
pp. 251115 ◽  
Author(s):  
David S. Meyaard ◽  
Guan-Bo Lin ◽  
Qifeng Shan ◽  
Jaehee Cho ◽  
E. Fred Schubert ◽  
...  
Keyword(s):  
Carrier Transport ◽  
Light Emitting Diodes ◽  
Efficiency Droop ◽  
Light Emitting
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