Abstract
In this work, InGaN/GaN light-emitting diodes (LEDs) possessing varied quantum well (QW) numbers were systematically investigated both numerically and experimentally. The numerical computations show that with the increased QW number, a reduced electron leakage can be achieved and hence the efficiency droop can be reduced when a constant Shockley-Read-Hall (SRH) nonradiative recombination lifetime is used for all the samples. However, the experimental results indicate that, though the efficiency droop is suppressed, the LED optical power is first improved and then degraded with the increasing QW number. The analysis of the measured external quantum efficiency (EQE) with the increasing current revealed that an increasingly dominant SRH nonradiative recombination is induced with more epitaxial QWs, which can be related to the defect generation due to the strain relaxation, especially when the effective thickness exceeds the critical thickness. These observations were further supported by the carrier lifetime measurement using a pico-second time-resolved photoluminescence (TRPL) system, which allowed for a revised numerical modeling with the different SRH lifetimes considered. This work provides useful guidelines on choosing the critical QW number when designing LED structures.
Highlights
Owing to the advantages of high efficiency, long lifespan, high reliability, controllable color properties and ease of digitalization, GaN-based light-emitting diodes (LEDs) are considered as the generation lighting sources to replace the traditional lighting devices of incandescent and fluorescent lamps [1, 2]
The numerical computations show that with the increased quantum well (QW) number, a reduced electron leakage can be achieved and the efficiency droop can be reduced when a constant Shockley-Read-Hall (SRH) nonradiative recombination lifetime is used for all the samples
The analysis of the measured external quantum efficiency (EQE) with the increasing current revealed that an increasingly dominant SRH nonradiative recombination is induced with more epitaxial QWs, which can be related to the defect generation due to the strain relaxation, especially when the effective thickness exceeds the critical thickness
Summary
Owing to the advantages of high efficiency, long lifespan, high reliability, controllable color properties and ease of digitalization, GaN-based LEDs are considered as the generation lighting sources to replace the traditional lighting devices of incandescent and fluorescent lamps [1, 2]. Despite these advantages and the dramatic progress being made in GaN-based LED research, development and commercialization, these LEDs still suffer from a serious efficiency droop under high current density injection, which limits the expansion of these devices in the general lighting market. The influence of InGaN QW number on the LED performance has previously been studied and reported. The influence of QW number on the performance of LED devices is understood by systematic analysis
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