Carrier distribution in (0001)InGaN∕GaN multiple quantum well light-emitting diodes

Abstract

We study the carrier distribution in multi quantum well (multi-QW) InGaN light-emitting diodes. Conventional wisdom would assume that a large number of QWs lead to a smaller carrier density per QW, enabling efficient carrier recombination at high currents. We use angle-resolved far-field measurements to determine the location of spontaneous emission in a series of multi-QW samples. They reveal that, no matter how many QWs are grown, only the QW nearest the p layer emits light under electrical pumping, which can limit the performances of high-power devices.

Role of substrate quality on the performance of semipolar (112¯2) InGaN light-emitting diodes

“…31 The "efficiency droop" is a common issue in nitride LEDs, 37,38 which is caused by a non-radiative carrier loss mechanism that has small effect at low J inject present in the active region, but becomes dominant at higher J inject. The main reason of the droop is still under debate as many different mechanisms have been proposed including Auger recombination, [39][40][41][42] "carrier overflow"/poor hole-injection efficiency, 35,43,44 and density-activated defects. 45,46 Generally, the much smaller droop of nonpolar and semipolar LEDs in comparison with polar LEDs has been attributed to the weaker polarization fields.…”

“…56 Additionally, the rough surface morphology of the PSS-LED (Fig. 1) is another issue as it can cause nonuniform carrier distribution 21,44 and compositional fluctuations. 21 It has been previously found that polished PSS-GaN substrates can strongly enhance the luminescence uniformity of QWs and the performance of PSS-LEDs.…”

“…It should be noted that in an MQW structure under PL excitation, electron-hole pairs are generated in the whole structure, whereas under EL excitation, the generated carriers are mostly distributed in the QW nearest the p-layer. 44,52 For InGaN QW structures, it is well-known that TDs strongly affect IQE as they can act as non-radiative recombination centres. 25,[53][54][55] However, it has been found that a strong ELOC can effectively reduce the QW excitons from being trapped into TDs, resulting in an enhanced luminescence efficiency from InGaN based devices.…”

Carrier distribution in InGaN/GaN tricolor multiple quantum well light emitting diodes

“…In situations where all quantum wells are identical, the relatively large effective mass of the holes, as compared to the effective mass of the electrons, tends to make hole transport the limiting factor in achieving a uniform carrier distribution. 8 The effect of barrier thickness on carrier distribution has also been studied in InGaAsP lasers where a large valence band offset is present. 9 Apart from their use in monitoring carrier distributions, multicolor LEDs are also useful as broad-spectrum LED sources.…”

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.…”