EFFICIENCY DROOP IN GaInN HIGH-POWER LIGHT-EMITTING DIODES

GaN -based light-emitting diodes suffer from high-current loss mechanisms that lead to a significant decrease in internal quantum efficiency at high drive currents. This phenomenon, known as "efficiency droop," is a major problem for solid-state lighting applications, in which light-emitting diodes are driven at high currents to deliver large optical powers. Although substantial effort has been invested to uncover the physical origin and mitigate the effects of efficiency droop, there is still a lack of consensus on the dominant mechanism responsible. In this article, we review several mechanisms that have been proposed as explanations of efficiency droop, including junction heating, carrier delocalization, Auger recombination, and electron leakage from the active region. In addition, device structures intended to mitigate the droop-causing mechanism – (i) thick quantum wellsl, (ii) enhanced hole-injection efficiency structures, and (iii) polarization-matched active region – are discussed.

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Improved Performance of Electron Blocking Layer Free AlGaN Deep Ultraviolet Light-Emitting Diodes Using Graded Staircase Barriers

Micromachines ◽

10.3390/mi12030334 ◽

2021 ◽

Vol 12 (3) ◽

pp. 334

Author(s):

Barsha Jain ◽

Ravi Teja Velpula ◽

Moulik Patel ◽

Sharif Md. Sadaf ◽

Hieu Pham Trung Nguyen

Keyword(s):

Active Region ◽

Light Emitting Diodes ◽

Internal Quantum Efficiency ◽

Hole Injection ◽

Blocking Layer ◽

Electron Blocking Layer ◽

Injection Efficiency ◽

Light Emitting ◽

Electron Leakage ◽

Deep Ultraviolet

To prevent electron leakage in deep ultraviolet (UV) AlGaN light-emitting diodes (LEDs), Al-rich p-type AlxGa(1−x)N electron blocking layer (EBL) has been utilized. However, the conventional EBL can mitigate the electron overflow only up to some extent and adversely, holes are depleted in the EBL due to the formation of positive sheet polarization charges at the heterointerface of the last quantum barrier (QB)/EBL. Subsequently, the hole injection efficiency of the LED is severely limited. In this regard, we propose an EBL-free AlGaN deep UV LED structure using graded staircase quantum barriers (GSQBs) instead of conventional QBs without affecting the hole injection efficiency. The reported structure exhibits significantly reduced thermal velocity and mean free path of electrons in the active region, thus greatly confines the electrons over there and tremendously decreases the electron leakage into the p-region. Moreover, such specially designed QBs reduce the quantum-confined Stark effect in the active region, thereby improves the electron and hole wavefunctions overlap. As a result, both the internal quantum efficiency and output power of the GSQB structure are ~2.13 times higher than the conventional structure at 60 mA. Importantly, our proposed structure exhibits only ~20.68% efficiency droop during 0–60 mA injection current, which is significantly lower compared to the regular structure.

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Improving hole injection from p-EBL down to the end of active region by simply playing with polarization effect for AlGaN based DUV light-emitting diodes

AIP Advances ◽

10.1063/5.0007460 ◽

2020 ◽

Vol 10 (6) ◽

pp. 065032

Author(s):

Danyang Zhang ◽

Chunshuang Chu ◽

Kangkai Tian ◽

Jianquan Kou ◽

Wengang Bi ◽

...

Keyword(s):

Active Region ◽

Polarization Effect ◽

Light Emitting Diodes ◽

Hole Injection ◽

Light Emitting

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Hole injection and efficiency droop improvement in InGaN/GaN light-emitting diodes by band-engineered electron blocking layer

Applied Physics Letters ◽

10.1063/1.3531753 ◽

2010 ◽

Vol 97 (26) ◽

pp. 261103 ◽

Cited By ~ 164

Author(s):

C. H. Wang ◽

C. C. Ke ◽

C. Y. Lee ◽

S. P. Chang ◽

W. T. Chang ◽

...

Keyword(s):

Light Emitting Diodes ◽

Efficiency Droop ◽

Hole Injection ◽

Blocking Layer ◽

Electron Blocking Layer ◽

Light Emitting

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

International Journal of High Speed Electronics and Systems ◽

10.1142/s0129156415200086 ◽

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.

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