Determination of the coefficient of light attenuation in thin layers of light-emitting diodes

Pivotal role of ballistic and quasi-ballistic electrons on LED efficiency

“…Last but not least, junction Joule heating effect on LED efficiency deserves a close attention as it has also been proposed to contribute to the InGaN LED efficiency drop, indicating the obvious need for optimal heat removal [37]. The junction heating issue is very important due to several reasons.…”

“…Despite substantial progress on the performance front, the physical origin of the efficiency drop in InGaN LEDs is not understood with sufficient clarity as of yet and is open to further investigations, a prerequisite for the remedies to be found and implemented. Among the various causes proposed for the observed efficiency degradation are Auger recombination [5], current roll-off resulting from phonon-assisted tunneling through defect sites [6], poor hole injection [7][8][9], polarization field [10,11], and junction heating [12], as well as current crowding and related contact degradation. Junction heating can be mitigated by increasing the efficiency and employment of packages capable of removing the dissipated heat very efficiently, both of which are the subject of vigorous developmental efforts in industry.…”

Design of electron blocking layers for improving internal quantum efficiency of InGaN/AlGaN-based ultraviolet light-emitting diodes

“…Thirdly, the performance of LEDs is still limited by a critical problem called efficiency droop, which decreases the internal quantum efficiency (IQE) at high current. Junction heating [4], Auger recombination [5], carrier leakage [6], and polarization effect [7] have all been suggested to explain this efficiency droop. Although the efficiency droop phenomenon in LEDs remains unsolved, the Auger recombination issue related to carrier densities and polarization effect has been at the center of focus in efficiency droop research.…”

Advantages of GaN based light-emitting diodes with p-AlGaN/InGaN superlattice last quantum barrier

“…Nevertheless, to replace the traditional light source completely with light-emitting diodes, the efficiency droop of LEDs should be further improved. In recent years, people have proposed some possible physical mechanisms for efficiency droop such as poor hole injection efficiency [4], electron leakage [5], polarization effect [6], junction heating [7], carrier delocalization [8], the quantum confined stark effect (QCSE) [9], and the Auger recombination [10]. Among the numerous factors, the severe electron leakage and the poor hole injection efficiency are perceived as a key factor for this issue which has been identified by Wang et al [11] In order to overcome the problem, scientists have proposed various effective structures from many point of views, such as the usage of AlGaN barriers [12], InGaN-AlGaN-InGaN barriers [13], staggered quantum wells (QWs) [14], graded electron blocking layer (EBL) [15], AlGaN/GaN superlattice EBL of gradual Al mole fraction [16] and hole reservoir layer [17] In this work, the performance is improved mainly by adjusting the last quantum barrier of LEDs.…”