Defects and Reliability of GaN‐Based LEDs: Review and Perspectives

Abstract

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.

Lifetime Prediction of Current-and Temperature-Induced Degradation in Silicone-Encapsulated 365 nm High-Power Light-Emitting Diodes

“…c.) Auger-driven recombination: Recent studies [58], [59], [60], [61] suggest a new type of Auger-driven recombination process. The process is different from classical Auger recombination due to its dependence on trap concentration.…”

“…As a result of its quadratic dependence on carrier density and its relation with defect density, this process could drive the degradation of optoelectronic GaN structures. Since this recombination mechanism has been proposed recently, its effect on optical power depreciation has not been fully investigated [61].…”

Analysis of defect-related optical degradation of VCSILs for photonic integrated circuits

“…Figure 7b depicts the C-f characteristics measured at 1 V: the results indicate a capacitance decrease at around 100 kHz which can no longer be probed after the stress. The behavior observed in the unaged device can be related to the response of a defect placed at the edge of the space charge region (SCR) being filled and depleted in accordance with the small signal variation (VAC) [16]. By employing thermal admittance spectroscopy (TAS) [17] we related the small signal capacitance inflection point with the thermal emission of the trap, described in the following relation:…”

Structural Engineering in a Microscale Laser Diode with InGaN Tunnel-Junction Nanorods

“…High-brightness and high-definition light sources with an ultracompact size are required for next-generation augmented reality (AR) and virtual reality (VR) display applications . Micro-LED is emerging as one of the most promising candidates with higher pixel density, a fast fresh rate, and low power consumption. − Because of the advantages of maximizing luminous efficiency through a direct transition bandgap and realizing the full visible light range from 400 nm violet wavelength to 700 nm red wavelength by changing the indium composition, GaN-based LED materials are expected to be used in micro-LED devices. , However, current micro-GaN LEDs show a severe external quantum efficiency drop as the size decreases to the 5 μm × 5 μm area. The micro-LEDs are typically manufactured through a dry-etching method, which results in a serious decrease in the luminous efficiency due to physical damage and area reduction in the InGaN active region.…”

“…1−4 Because of the advantages of maximizing luminous efficiency through a direct transition bandgap and realizing the full visible light range from 400 nm violet wavelength to 700 nm red wavelength by changing the indium composition, GaN-based LED materials are expected to be used in micro-LED devices. 5,6 However, current micro-GaN LEDs show a severe external quantum efficiency drop as the size decreases to the 5 μm × 5 μm area. The micro-LEDs are typically manufactured through a dry-etching method, which results in a serious decrease in the luminous efficiency due to physical damage and area reduction in the InGaN active region.…”