Herein, the main factors and mechanisms that limit the reliability of gallium nitride (GaN)-based light-emitting diodes (LEDs) are reviewed. An overview of the defects characterization techniques most relevant for wide-bandgap diodes is provided first. Then, by introducing a catalogue of traps and deep levels in GaN and computer-aided simulations, it is shown which types of defects are more detrimental for the radiative efficiency of the devices. Gradual degradation mechanisms are analyzed in terms of their specific driving force: a separate analysis of recombination-enhanced processes, driven by nonradiative recombination and/or temperature-assisted processes, such as defects or impurity diffusion, is presented. The most common lifetime estimation methods and standards adopted for solid-state luminaires are also reported on. Finally, the paper concludes by examining which are the typical degradation and failure mechanisms exhibited by LEDs submitted to electrical overstress.

Defects can significantly modify the electro-optical characteristics of InGaN light-emitting diodes (LEDs); however, modeling the impact of defects on the electrical characteristics of LEDs is not straightforward. In this paper, we present an extensive investigation and modeling of the impact of defects on the electrical characteristics of InGaN-based LEDs, as a function of the thickness of the quantum well (QW). First, we demonstrate that the density of defects in the active region of III-N LEDs scales with increasing thickness of the InGaN QW. Since device layers with high indium content tend to incorporate more defects, we ascribed this experimental evidence to the increased volume of defects-rich InGaN associated to thicker InGaN layers. Second, we demonstrate that the current-voltage characteristics of the devices are significantly influenced by the presence of defects, especially in the sub turn-on region. Specifically, we show that the electrical characteristics can be effectively modeled in a wide current range (from pA to mA), by considering the existence of trap-assisted tunneling processes. A good correspondence is obtained between the experimental and simulated electrical characteristics (I-V), by using-in the simulation-the actual defect concentrations/activation energies extracted from steady-state photocapacitance, instead of generic fitting parameters.

The long-term stability of ultraviolet (UV)-C light-emitting diodes (LEDs) is of major importance for many applications. To improve the understanding in this field, we analyzed the degradation of AlGaN-based UVC LEDs and modeled the variation of electrical characteristics by 2D simulations based on the results of deep-level optical spectroscopy (DLOS). The increase in the forward leakage current observed during ageing was ascribed an increase in trap-assisted tunneling. The analysis of the degradation kinetics suggests the role of a defect diffusion process, possibly involving impurities coming from the p-type layers.

We investigate the density of defects and the degradation rate in InGaN light-emitting diodes having identical dislocation density and epitaxial structure, but different indium content in the quantum well (QW; 12%, 16%, 20%). Our results, based on combined steady-state photocapacitance, light-capacitance voltage, and degradation measurements indicate that: (a) the density of defects in the superlattice underlayer is identical for the three wafers, indicating good and reproducible growth conditions; (b) the density of defects within the active region of the devices shows a monotonic dependence on the indium content in the QWs. These results, consistent with previous studies on the topic, prove unequivocally the important role of indium in favoring the incorporation of point defects, further clarifying the possible mechanisms of defect formation, and give a quantitative assessment of the related effect; (c) in step-stress experiments, the degradation rate was found to be much stronger for devices having high indium content in the QW. This result can be explained by considering a decrease in injection efficiency due to the generation or transport of defects, or an increment in defect-assisted Auger recombination terms due to the propagation of defects.

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The lifetime of deep-ultraviolet light-emitting diodes (LEDs) is still limited by a number of factors, which are mainly related to semiconductor defects, and still need to be clarified. This paper improves the understanding of UV LED degradation, by presenting an analysis based on combined deep-level transient spectroscopy (C-DLTS), electro-optical characterization, and simulations, carried out before and during a constant current stress test. The original results of this paper are (i) C-DLTS measurements allowed us to identify three traps, two associated with Mg-related defects, also detected in the unaged device, and one related to point defects that were generated by the ageing procedure. (ii) Based on these results and on TCAD simulations, we explain the variation in the forward I–V by the degradation of the p-contact, due to Mg passivation. (iii) On the other hand, optical degradation is ascribed to an increase in defectiveness of the active region and surrounding areas, which led to a decrease in injection efficiency, to an increase in non-radiative recombination, and to an increase in trap-assisted tunneling processes.

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III-N light-emitting-diodes (LEDs) are subject of intense investigations, thanks to their high efficiency and great reliability. The quality of the semiconductor material has a significant impact on the electro-optical performance of LEDs: for this reason, a detailed characterization of defect properties and the modeling of the impact of defects on device performance are of fundamental importance. This presentation addresses this issue, by discussing a set of recent case studies on the topic; specifically, we focus on the experimental characterization of defects, and on the modeling of their impact on the electro-optical characteristics of the devices.