Two kinds of InGaN-based light-emitting diodes (LEDs) are investigated to understand the nonradiative carrier recombination processes. Various temperature-dependent measurements such as external quantum efficiency, current-voltage, and electroluminescence spectra are utilized from 50 to 300 K. Based on these experimental results, we analyze the dominant nonradiative recombination mechanism for each LED device. We also analyze the effect of the dominant nonradiative recombination mechanism on the efficiency droop. On the basis of correlation between the efficiency droop and nonradiative recombination mechanisms, we discuss an approach to reducing the efficiency droop for each LED device.

We investigate the nonradiative recombination mechanisms of two conventional InGaN/GaN-based blue light-emitting diodes with different threading dislocation densities (TDDs). The current–voltage, the ideality factor, and the slope of the light-versus-current curve on log scales are analyzed to distinguish the dominant nonradiative recombination mechanisms at room temperature. Through the analysis, we infer the dominant nonradiative recombination mechanisms to be the Shockley–Read–Hall process for the sample with a low TDD (∼1 × 108 cm−2) and the defect-assisted tunneling for the sample with a high TDD (∼1 × 109 cm−2). For more detailed analysis of the nonradiative recombination mechanisms and their impacts on the device performance, we execute the temperature-dependent photovoltage and temperature-dependent electroluminescence efficiency experiments. The sample with a low TDD is found to be more prone to the carrier spill-over at cryogenic temperatures due to the deactivation of point defects, while the sample with a high TDD is more robust to the operation at cryogenic temperatures owing to the relative insensitiveness of the defect-assisted tunneling to temperature.

To improve the internal quantum efficiency of green light-emitting diodes, we present the numerical design and analysis of bandgap-engineered W-shaped quantum well. The numerical results suggest significant improvement in the internal quantum efficiency of the proposed W-LED. The improvement is associated with significantly improved hole confinement due to the localization of indium in the active region, leading to improved radiative recombination rate. In addition, the proposed device shows reduced defect-assisted Shockley-Read-Hall (SRH) recombination rate as well as Auger recombination rate. Moreover, the efficiency rolloff in the proposed device is associated with increased built-in electromechanical field.

Metal-halide perovskite light-emitting diodes (PeLEDs) are considered as new-generation highly efficient luminescent materials for application in displays and solid-state lighting. Since the first successful demonstration of PeLEDs in 2014, the research on the development of efficient PeLEDs has progressed significantly. Although the device efficiency has significantly improved over a short period of time, their overall performance has not yet reached the levels of mature technologies for practical applications. Various degradation processes are the major impediment to improving the performance and stability of PeLED devices. In this review, we discuss various analysis techniques that are necessary to gain insights into the effects of various degradation mechanisms on the performance and stability of PeLEDs. Based on the causes and effects of external and internal factors, the degradation processes and associated mechanisms are examined in terms of critical physical and chemical parameters. Further, according to the progress of the current research, the challenges faced in studying degradation mechanisms are also elucidated. Given the universality of the degradation behavior, an in-depth understanding of the device degradation may promote the development of optimization strategies and further improve the performance and stability of PeLEDs.

As the latest applications of LEDs require more harsh operating conditions, understanding the device thermal properties becomes more essential for further improving the device efficiencies. In applications where heat dissipation can be a critical issue, thermoreflectance (TR) can be utilized as a useful noncontact measurement technique for analyzing the thermal properties. In this paper, we investigate the TR method of measuring the surface temperature, using a lateral-type blue LED chip under high-power operation. The TR we employ measures the change in reflectivity from the Au metal electrode. By comparing with surface/junction temperatures measured by other methods based on the thermocouple and the forward voltage, we find that the TR method can provide accurate and reliable results of measuring the surface temperature of modern LEDs. A useful insight can also be obtained from the temperature distribution on the LED chip surface.

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Degradation phenomena of GaN-based blue LEDs are investigated from comprehensive electrical, optical, and thermal analyses. After constant reverse-bias stress, the LED sample under investigation shows permanent degradations indicated by increases both in the tunneling/sidewall leakage current in the low-current region and the nonradiative current in the high-current region. A subsequent decrease in series resistance and increase in junction temperature are also observed. The degradation at high currents is analyzed in terms of the radiative recombination current utilizing the information of the internal quantum efficiency (IQE), which has been rarely attempted. All of the observed degradations can be attributed to the increase in defect density in the active layer of the LED chip under reverse-bias stress. This work emphasizes that many important reliability-related features of LEDs are functions of defects and the junction temperature and that the IQE can provide crucial information in the analysis. The increased junction temperature would have further detrimental effects on the device performance and eventually lead to device failure. The analyses presented in this work shed more light on understanding the degradation phenomena in the GaN-based LEDs under reverse-bias stress.