Degradation mechanisms of InGaN visible LEDs and AlGaN UV LEDs

Santi, Carlo De; Caria, Alessandro; Piva, Francesco; Meneghesso, Gaudenzio; Zanoni, Enrico; Meneghini, Matteo

doi:10.1016/b978-0-12-819254-2.00001-1

Cited by 10 publications

(7 citation statements)

References 106 publications

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“…There is significant research underway to improve the performance of AlGaN UV LEDs with the expectation that large price reductions will occur within the next few years for sources for UV-B and UV-C radiation. However, there are significant technical challenges impacting the performance and reliability of AlGaN UV LEDs that need to be addressed including developing a transparent p-contact material, reducing the defect density of both n-doped and p-doped materials, improving radiation extraction efficiency, and developing a mirror with high reflectivity between 220 and 340 nm [7,[11][12][13][14]. These technical challenges can be largely divided into electrical and optical challenges and some examples are given in Figure 1-3.…”

Section: Light-emitting Diodesmentioning

confidence: 99%

“…The small current flow before Vth is indicative of defects in the epitaxial layer that promote non-radiative recombination of electrons and holes mostly through Shockley-Read-Hall (SRH) processes. Trap-assisted tunneling (TAT) is the main mechanism responsible for the SRH currents in UV LEDs [13].…”

Section: Current (A)mentioning

confidence: 99%

“…Because of the absence of overlap of the primary and secondary peak emissions, the latter did not impact the FWHM value of the main peak but it still made a significant contribution to the total radiation. This secondary peak likely arises from deep-level states in the epitaxial layer resulting from defects (e.g., magnesium-acceptor traps) [8,13,21]. This effect was most pronounced for UV-7 (see…”

Section: Initial Radiometric Measurementsmentioning

confidence: 99%

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Initial Benchmarks of UV LEDs and Comparisons with White LEDs

Davis¹,

Rountree²

2021

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Light-emitting diodes (LEDs) can emit radiation that spans the range from near infrared (IR) to all three bands of ultraviolet (UV) radiation (i.e., UV-A, UV-B, UV-C). These emission sources are fabricated by varying doping levels of the aluminum gallium indium nitride (AlGaInN) alloy system, which tunes the emission wavelength of the semiconductor. During the past 20 years, the blue LED, made from InGaN, has advanced technologically to the point that it now provides the backbone for the solid-state lighting revolution that is occurring in general illumination. With proper doping, the InGaN alloy system can be extended to UV-A emission wavelengths as low as 362 nanometers (nm); however, producing LEDs that emit in the UV-B and UV-C bands requires the use of AlGaN alloys. Unfortunately, AlGaN semiconductors are not at the same level of technological development as InGaN, and LEDs made from AlGaN suffer from a variety of inefficiencies arising from electrical and optical limitations of the current technology. This report is aimed at benchmarking the performance of UV LEDs across all three bands in an effort to understand the current state of the technology.UV sources have many industrial applications, and their total market exceeds $750 million. Examples of applications for UV sources include ink and polymer curing (primarily UV-A sources), medical treatments (primarily UV-B sources), and disinfection (primarily UV-C sources). While UV-A applications are the largest market today, the increased need for surface and air disinfection is expected to create a significant market opportunity for UV-C sources in the near future. The current technology most widely used for UV sources in all three bands is the mercury discharge lamp, which has moderate energy efficiency but also has a number of limitations including compatibility with compact form factors, long-term reliability, and end-oflife issues associated with disposing a glass tube containing mercury without creating environmental contamination. UV LEDs have the potential to displace mercury lamps in UV applications in much the same way that white LEDs have displaced fluorescent lamps in many commercial and residential lighting markets.The primary goal of this report is to benchmark the initial level of performance of a selection of commercial UV LEDs across all three bands (i.e., UV-A, UV-B, UV-C). To provide the initial performance benchmarks, a test matrix containing 13 different UV LED products was created in association with the LED Systems Reliability Consortium (LSRC). The products in this test matrix were all commercially available as of June 2021, and at least 22 samples of each product were tested. In addition, two common, commercial white LEDs were tested to provide a benchmark against blue-pumped white LEDs. Testing of the samples included electrical performance testing (e.g., current-voltage measurements) and photometric testing in a calibrated integrating sphere capable of measuring devices in the UV-A, UV-B, and UV-C bands. The electrical testing provid...

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Section: Light-emitting Diodesmentioning

confidence: 99%

Section: Current (A)mentioning

confidence: 99%

Section: Initial Radiometric Measurementsmentioning

confidence: 99%

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Initial Benchmarks of UV LEDs and Comparisons with White LEDs

Davis¹,

Rountree²

2021

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“…However, an analysis of diffusion process in GaN-based solar cells has never been carried out. In these GaN-based high periodicity InGaN-GaN MQWs solar cells, Mg, H (which is incorporated into the p-type layers during MOCVD growth with high density even after Mg activation annealing 18 ), and other impurities such as oxygen (coming from the ITO/p + -GaN layer 19 ) can easily diffuse from the p-GaN layer of the device to the active region, also through dislocations, in thermally activated diffusion process 20 7 . The model proposed by van Opdorp and 't Hooft 9 allows to evaluate the recombination lifetime during stress, from the analysis of the sub-threshold L-I data.…”

Section: Diffusion Modelmentioning

confidence: 99%

Degradation of GaN-based InGaN-GaN MQWs solar cells caused by thermally-activated diffusion

Nicoletto

Caria²,

Santi

et al. 2023

Gallium Nitride Materials and Devices XVIII

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We investigate the degradation of high-periodicity GaN-based InGaN-GaN multiple quantum wells (MQWs) solar cells submitted to stress under high excitation intensity and high temperature; stress conditions are chosen to investigate cell behavior in a harsh scenario, such as wireless power transfer systems, space applications and concentrator harvesting systems. By examining the decrease in the short-circuit current and electroluminescence of these devices and the increase in the forward current at low bias, we suggest the presence of a thermally-activated diffusion process of impurities from the p-side of the device toward the active region. This process favors the increase in the Shockley-Read-Hall (SRH) recombination rate. By employing the van Opdorp and t'Hooft model, we analyzed the time-variation of non-radiative Shockley-Read-Hall lifetime during aging, extracting the diffusion coefficient of the defect involved in the degradation; we also extracted the related activation energy by an appropriate fitting of the degradation kinetics according to Fick's second law of diffusion. The obtained values suggest that degradation originates from the diffusion of hydrogen, whose severity depends also on the thickness of the p-GaN layer of these devices. The proposed analysis methods and the obtained results are useful for understanding the physics of multiple quantum wells (MQWs) solar cells during degradation. The results can be used to increase the performance and reliability in novel applications where these devices are proposed, such us additional layer in multi-junction (MJ) solar cells, and the application in harsh environments.

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“…The possibility of developing a low-cost fast robust and mobile disinfection system for surfaces [1]- [4] based on LEDs instead of conventional mercury lamps, enticed studies in the UV-C LED field. Up to now lifetime studies of UV-C LEDs identified to main areas of degradation: the degradation of the p-contact, and the decrease in EQE caused by the generation of defects during the ageing [5]- [9]. For these reasons we investigated the degradation mechanisms of single quantum well (SQW) LEDs with an emission wavelength of 265 nm, subjected to a stress at the nominal current density of 100 A•cm -2 at the temperature of 40 °C.…”

Section: Introductionmentioning

confidence: 99%

Degradation of AlGaN-based SQW UV-C LEDs investigated by capacitance deep level transient spectroscopy

Piva

Buffolo²,

Santi³

et al. 2023

Gallium Nitride Materials and Devices XVIII

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The market of Ultraviolet (UV) Light Emitting Diodes (LEDs) is expected to expand substantially in the coming years, thanks to the disinfection properties of the UV light; however, a detailed study on the reliability-limiting processes is a fundamental step, for an effective deployment of this technology. We investigated the degradation mechanisms of AlGaN-based UV Single Quantum Well (SQW) LEDs, with a nominal emission wavelength of 265 nm, an area of 0.1 mm2 and a nominal current density of 100 A·cm-2. By means of constant current stress test and Capacitance Deep Level Transient Spectroscopy (C-DLTS) we studied the main electrical, optical, spectral and capacitance characteristics of the devices, in order to understand the dominant causes of degradation. For aged devices the electrical characterization shows increased subthreshold leakage currents, due to the increase in Trap Assisted Tunneling (TAT) components, as well as an increase in drive voltage, which is ascribed to contact degradation or a decrease in injection efficiency. The optical output power showed a decrease especially at low current levels, which has been ascribed to an increase in non-radiative recombination and suggests the generation of defects in the LED active region. C-DLTS measurements showed in unaged devices the presence of two defects in the structure, both ascribed to magnesium (Mg), located at 475 meV and 150 meV from the respective band. Moreover, we detected the increase in concentration of a third defect during the stress test with an activation energy of 700 meV, that acts as a point defect, and could be ascribed to gallium vacancies or nitrogen antisites.

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Degradation mechanisms of InGaN visible LEDs and AlGaN UV LEDs

Cited by 10 publications

References 106 publications

Initial Benchmarks of UV LEDs and Comparisons with White LEDs

Initial Benchmarks of UV LEDs and Comparisons with White LEDs

Degradation of GaN-based InGaN-GaN MQWs solar cells caused by thermally-activated diffusion

Degradation of AlGaN-based SQW UV-C LEDs investigated by capacitance deep level transient spectroscopy

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