Efficiency droop in nitride‐based light‐emitting diodes

Abstract

Nitride‐based light‐emitting diodes (LEDs) suffer from a reduction (droop) of the internal quantum efficiency with increasing injection current. This droop phenomenon is currently the subject of intense research worldwide, as it delays general lighting applications of GaN‐based LEDs. Several explanations of the efficiency droop have been proposed in recent years, but none is widely accepted. This feature article provides a snapshot of the present state of droop research, reviews currently discussed droop mechanisms, contextualizes them, and proposes a simple yet unified model for the LED efficiency droop.magnified image Illustration of LED efficiency droop (details in Fig. 13).

Identification of nnp and npp Auger recombination as significant contributor to the efficiency droop in (GaIn)N quantum wells by visualization of hot carriers in photoluminescence

“…Despite great progress in recent years, resulting in peak power conversion efficiencies of up to 81%, 1 one obstacle still to overcome is the decrease in efficiency towards high operating current densities, a phenomenon commonly known as droop. 2,3 The current dependency of the internal quantum efficiency (IQE) can be modeled in good quantitative agreement with experimental data using an ABC rate equation model [4][5][6] IQE ¼ Bn 2 An þ Bn 2 þ Cn 3 ;…”

Determination of recombination coefficients in InGaN quantum-well light-emitting diodes by small-signal time-resolved photoluminescence

“…2,11) In this model, assuming an injection efficiency of 100% (i.e. in the absence of electron and hole leakage from the active region), the external quantum efficiency (EQE) of an LED is given by:…”

“…the reduction of efficiency with increasing drive current, 1,2) which has been discussed widely in literature and has been attributed to Auger recombination [3][4][5] experimentally. In addition, an extension of the emission wavelength into the "Green Gap" 1,6) has proven to be challenging.…”

Defect recombination induced by density-activated carrier diffusion in nonpolar InGaN quantum wells

“…[1][2][3] In the past decade, multiple mechanisms have been proposed to explain the efficiency droop including Auger recombination induced by multi-particle interactions, [4][5][6][7][8] electron leakage due to poor hole injection and electron overflow, 9,10 carrier loss related to reduction or saturation of carrier localization, 11,12 and other processes including the density-activated defect recombination (DADR). 13,14 Some of these factors have been found to be tightly associated with the internal polarization field.…”