Low efficiency droop in blue-green m-plane InGaN/GaN light emitting diodes

Abstract

We investigated the electroluminescence and relatively external quantum efficiency (EQE) of m-plane InGaN/GaN light emitting diodes (LEDs) emitting at 480 nm to elucidate the droop behaviors in nitride-based LEDs. With increasing the injection current density to 100 A/cm2, the m-plane LEDs exhibit only 13% efficiency droop, whereas conventional c-plane LEDs suffer from efficiency droop at very low injection current density and the EQE of c-plane LEDs decrease to as little as 50% of its maximum value. Our simulation models show that in m-plane LEDs the absence of polarization fields manifest not only the hole distribution more uniform among the wells but also the reduction in electron overflow out of electron blocking layer. These results suggest that the nonuniform distribution of holes and electron leakage current due to strong polarization fields are responsible for the relatively significant efficiency droop of conventional c-plane LEDs.

Comparative studies of efficiency droop in polar and non-polar InGaN quantum wells

“…Several groups have linked this behaviour directly to the absence of the internal electric fields. From measurements on non-polar LEDs, Ling et al 18 and Li et al 19 assigned the reduction in droop to reduced losses associated with carrier spill over due to the improved carrier confinement. However, an alternative explanation was put forward by Li et al 20 and Chang et al 21 who suggested that droop was reduced because of the improvement in hole distribution amongst the QWs in multiple QW LEDs.…”

Self-screening of the quantum confined Stark effect by the polarization induced bulk charges in the quantum barriers

“…One way to reduce the QCSE is to suppress the polarization by growing the InGaN/GaN LEDs along those nonpolar or semipolar orientations. [8][9][10][11] Even in LEDs grown along [0001] orientation, the polarization in the InGaN/GaN MQWs can be suppressed by embedding the InGaN quantum well between the polarization matched quaternary AlInGaN quantum barriers. 12 Apart from the above methods, the polarization induced electric field within the quantum wells can be screened by Si doping the quantum barriers.…”

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

“…[19][20][21] Upon raising the current density to a level of 100 A/cm 2 , efficiency droop has been significantly reduced from 50% with polar QWs to 13% in nonpolar QWs. 21 Understanding the mechanism of the residual droop in nonpolar LEDs will be instrumental towards droop-free LED devices.…”

“…13,14 Some of these factors have been found to be tightly associated with the internal polarization field. [15][16][17][18][19][20][21] The reduction on internal polarization and the increase of hole concentrations in nonpolar QWs can efficiently suppress the loss during carrier injection. [19][20][21] Potentially, the interplay of polarization fields and Auger recombination in nonpolar QWs can be manipulated to optimize the device performance.…”

“…[15][16][17][18][19][20][21] The reduction on internal polarization and the increase of hole concentrations in nonpolar QWs can efficiently suppress the loss during carrier injection. [19][20][21] Potentially, the interplay of polarization fields and Auger recombination in nonpolar QWs can be manipulated to optimize the device performance. 16 These advantages make nonpolar QWs particularly suitable to achieve low droop devices.…”