Efficiency Drop in GreenInGaN/GaNLight Emitting Diodes: The Role of Random Alloy Fluctuations

Abstract

White light emitting diodes (LEDs) based on III-nitride InGaN/GaN quantum wells currently offer the highest overall efficiency for solid state lighting applications. Although current phosphor-converted white LEDs have high electricity-to-light conversion efficiencies, it has been recently pointed out that the full potential of solid state lighting could be exploited only by color mixing approaches without employing phosphor-based wavelength conversion. Such an approach requires direct emitting LEDs of different colors, including, in particular, the green-yellow range of the visible spectrum. This range, however, suffers from a systematic drop in efficiency, known as the "green gap," whose physical origin has not been understood completely so far. In this work, we show by atomistic simulations that a consistent part of the green gap in c-plane InGaN/GaN-based light emitting diodes may be attributed to a decrease in the radiative recombination coefficient with increasing indium content due to random fluctuations of the indium concentration naturally present in any InGaN alloy.

Evaluation of Light Extraction Efficiency of GaN-Based Nanorod Light-Emitting Diodes by Averaging over Source Positions and Polarizations

“…This "efficiency droop" phenomenon results in limited light output power at high current densities [6][7][8][9]. In addition, the EQE of GaN-based yellow-green LEDs with emission wavelengths from 530 to 600 nm has been reported to be <30%, which has been termed the "green gap" problem [10][11][12].…”

Indium gallium nitride-based ultraviolet, blue, and green light-emitting diodes functionalized with shallow periodic hole patterns

“…Gallium nitride (GaN)-based light-emitting diodes (LEDs) have recently become widespread in the fields of solid-state lighting, backlight units, automobile lighting, and outdoor full-colour displays because of their significantly lower energy consumption, longer lifetime, and higher brightness than conventional incandescent light bulbs 12345678. Moreover, the spectral range of indium gallium nitride (InGaN)/GaN multiple quantum wells (MQWs), which are typically used as active layers in InGaN-based LEDs, is from ultraviolet (UV) to green lights, with substantial light emission efficiency 91011.…”

Efficiency of True-Green Light Emitting Diodes: Non-Uniformity and Temperature Effects<strong> </strong>

“…[20,21]. Recently, implication of composition fluctuations in InGaN to the LED effi-324 ciency reduction in the "green gap" has been also demonstrated [22,23,24]. products of both sw-and lw-emission peaks are found to be nearly independent of temperature, similar to the case of blue LED [5].…”